rayforce-sys 1.1.2

/*
 *   Copyright (c) 2025-2026 Anton Kundenko <singaraiona@gmail.com>
 *   All rights reserved.

 *   Permission is hereby granted, free of charge, to any person obtaining a copy
 *   of this software and associated documentation files (the "Software"), to deal
 *   in the Software without restriction, including without limitation the rights
 *   to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *   copies of the Software, and to permit persons to whom the Software is
 *   furnished to do so, subject to the following conditions:

 *   The above copyright notice and this permission notice shall be included in all
 *   copies or substantial portions of the Software.

 *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *   AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 *   SOFTWARE.
 */

#include "lang/internal.h"
#include "ops/ops.h"
#include "ops/internal.h"
#include "ops/idxop.h"   /* RAY_IDX_CHUNK_ZONE fast path for min/max */
#include "mem/heap.h"

#include <stdlib.h>  /* qsort (introselect fallback) */

static int dbl_cmp(const void* a, const void* b) {
    double da = *(const double*)a, db = *(const double*)b;
    return (da > db) - (da < db);
}

/* Partition vals[lo..hi] so that vals[k] holds the kth-smallest element,
 * with everything to the left ≤ and everything to the right ≥.  Average
 * O(n) (Hoare quickselect with median-of-three), worst-case O(n log n)
 * via qsort fallback when recursion exceeds 2*log2(range).  Mirrors
 * std::nth_element's contract — the standard quantile/quickselect
 * pattern. */
static void nth_element_dbl(double* a, int64_t lo, int64_t hi, int64_t k) {
    int depth_limit = 0;
    for (int64_t r = hi - lo + 1; r > 0; r >>= 1) depth_limit++;
    depth_limit *= 2;
    while (hi - lo > 16) {
        if (depth_limit-- <= 0) {
            qsort(a + lo, (size_t)(hi - lo + 1), sizeof(double), dbl_cmp);
            return;
        }
        int64_t mid = lo + ((hi - lo) >> 1);
        if (a[lo] > a[mid]) { double t = a[lo]; a[lo] = a[mid]; a[mid] = t; }
        if (a[lo] > a[hi])  { double t = a[lo]; a[lo] = a[hi];  a[hi]  = t; }
        if (a[mid] > a[hi]) { double t = a[mid]; a[mid] = a[hi]; a[hi] = t; }
        /* Park pivot at hi-1; partition (lo, hi-1) with sentinels at both ends. */
        { double t = a[mid]; a[mid] = a[hi - 1]; a[hi - 1] = t; }
        double pivot = a[hi - 1];
        int64_t i = lo, j = hi - 1;
        for (;;) {
            while (a[++i] < pivot) {}
            while (a[--j] > pivot) {}
            if (i >= j) break;
            double t = a[i]; a[i] = a[j]; a[j] = t;
        }
        /* Restore pivot to its final resting position i. */
        { double t = a[i]; a[i] = a[hi - 1]; a[hi - 1] = t; }
        if      (k < i) hi = i - 1;
        else if (k > i) lo = i + 1;
        else            return;
    }
    /* Small range: insertion sort the slice covers vals[lo..hi]. */
    for (int64_t i = lo + 1; i <= hi; i++) {
        double key = a[i];
        int64_t j = i - 1;
        while (j >= lo && a[j] > key) { a[j + 1] = a[j]; j--; }
        a[j + 1] = key;
    }
}

/* ══════════════════════════════════════════
 * Aggregation builtins
 * ══════════════════════════════════════════ */

/* Build a one-op DAG over a single input vector and execute it. */
#define AGG_VEC_VIA_DAG(x, ctor) do {                       \
    ray_graph_t* g = ray_graph_new(NULL);                   \
    if (!g) return ray_error("oom", NULL);                  \
    ray_op_t* in = ray_graph_input_vec(g, x);              \
    ray_op_t* op = ctor(g, in);                            \
    return ray_lazy_wrap(g, op);                            \
} while(0)

static int agg_parted_numeric_base(int8_t t) {
    return t == RAY_BOOL || t == RAY_U8 || t == RAY_I16 ||
           t == RAY_I32 || t == RAY_I64 || t == RAY_F32 || t == RAY_F64 ||
           t == RAY_DATE || t == RAY_TIME || t == RAY_TIMESTAMP;
}

static int64_t agg_read_i64(ray_t* v, int64_t i) {
    void* d = ray_data(v);
    switch (v->type) {
    case RAY_BOOL:
    case RAY_U8: return ((uint8_t*)d)[i];
    case RAY_I16: return ((int16_t*)d)[i];
    case RAY_I32:
    case RAY_DATE:
    case RAY_TIME: return ((int32_t*)d)[i];
    case RAY_I64:
    case RAY_TIMESTAMP: return ((int64_t*)d)[i];
    default: return 0;
    }
}

static ray_t* agg_atom_i64_for_type(int8_t t, int64_t v) {
    switch (t) {
    case RAY_BOOL: return ray_bool(v != 0);
    case RAY_U8: return ray_u8((uint8_t)v);
    case RAY_I16: return ray_i16((int16_t)v);
    case RAY_I32: return ray_i32((int32_t)v);
    case RAY_DATE: return ray_date(v);
    case RAY_TIME: return ray_time(v);
    case RAY_TIMESTAMP: return ray_timestamp(v);
    default: return ray_i64(v);
    }
}

static ray_t* agg_parted_sum(ray_t* x) {
    int8_t base = (int8_t)RAY_PARTED_BASETYPE(x->type);
    /* Explicit runtime whitelist: numeric + duration-like TIME.  NOT
     * agg_type_admitted() — that is a permissive *plan-time* guard which only
     * rejects the types it KNOWS are bad and admits unknown wrappers (incl.
     * RAY_LIST); as the final runtime gate it would let a parted LIST column
     * fall into the integer loop and silently sum to 0.  DATE/TIMESTAMP are
     * absolute points and are rejected here too, matching flat sum (which
     * rejects them via agg_type_admitted); the parted path previously summed a
     * TIMESTAMP column instead. */
    if (!agg_parted_numeric_base(base) || base == RAY_DATE || base == RAY_TIMESTAMP)
        return ray_error("type", "sum expects a numeric or time-duration parted column, got %s", ray_type_name(base));
    ray_t** segs = (ray_t**)ray_data(x);
    if (base == RAY_F64 || base == RAY_F32) {
        double sum = 0.0;
        for (int64_t s = 0; s < x->len; s++) {
            ray_t* seg = segs[s];
            if (!seg) continue;
            int has_nulls = ray_vec_may_have_nulls(seg);
            for (int64_t i = 0; i < seg->len; i++)
                if (!has_nulls || !ray_vec_is_null(seg, i)) {
                    if (base == RAY_F64) sum += ((double*)ray_data(seg))[i];
                    else sum += (double)((float*)ray_data(seg))[i];
                }
        }
        return make_f64(sum);
    }
    int64_t sum = 0;
    for (int64_t s = 0; s < x->len; s++) {
        ray_t* seg = segs[s];
        if (!seg) continue;
        int has_nulls = ray_vec_may_have_nulls(seg);
        for (int64_t i = 0; i < seg->len; i++)
            if (!has_nulls || !ray_vec_is_null(seg, i)) sum = wrap_add_i64(sum, agg_read_i64(seg, i));
    }
    if (base == RAY_TIME) return ray_time(sum);
    return make_i64(sum);
}

static ray_t* agg_parted_avg(ray_t* x) {
    int8_t base = (int8_t)RAY_PARTED_BASETYPE(x->type);
    if (!agg_parted_numeric_base(base)) return ray_error("type", "avg expects a numeric or temporal parted column, got %s", ray_type_name(base));
    ray_t** segs = (ray_t**)ray_data(x);
    double sum = 0.0;
    int64_t cnt = 0;
    for (int64_t s = 0; s < x->len; s++) {
        ray_t* seg = segs[s];
        if (!seg) continue;
        int has_nulls = ray_vec_may_have_nulls(seg);
        if (base == RAY_F64 || base == RAY_F32) {
            for (int64_t i = 0; i < seg->len; i++) {
                if (has_nulls && ray_vec_is_null(seg, i)) continue;
                if (base == RAY_F64) sum += ((double*)ray_data(seg))[i];
                else sum += (double)((float*)ray_data(seg))[i];
                cnt++;
            }
        } else {
            for (int64_t i = 0; i < seg->len; i++) {
                if (has_nulls && ray_vec_is_null(seg, i)) continue;
                sum += (double)agg_read_i64(seg, i); cnt++;
            }
        }
    }
    if (cnt == 0) return ray_typed_null(-RAY_F64);
    return make_f64(sum / (double)cnt);
}

static ray_t* agg_parted_prod(ray_t* x) {
    int8_t base = (int8_t)RAY_PARTED_BASETYPE(x->type);
    if (!agg_parted_numeric_base(base) ||
        base == RAY_DATE || base == RAY_TIME || base == RAY_TIMESTAMP) {
        return ray_error("type", "prod expects a numeric parted column, got %s", ray_type_name(base));
    }
    ray_t** segs = (ray_t**)ray_data(x);
    if (base == RAY_F64 || base == RAY_F32) {
        double prod = 1.0;
        for (int64_t s = 0; s < x->len; s++) {
            ray_t* seg = segs[s];
            if (!seg) continue;
            int has_nulls = ray_vec_may_have_nulls(seg);
            for (int64_t i = 0; i < seg->len; i++) {
                if (has_nulls && ray_vec_is_null(seg, i)) continue;
                if (base == RAY_F64) prod *= ((double*)ray_data(seg))[i];
                else prod *= (double)((float*)ray_data(seg))[i];
            }
        }
        return make_f64(prod);
    }

    int64_t prod = 1;
    for (int64_t s = 0; s < x->len; s++) {
        ray_t* seg = segs[s];
        if (!seg) continue;
        int has_nulls = ray_vec_may_have_nulls(seg);
        for (int64_t i = 0; i < seg->len; i++) {
            if (has_nulls && ray_vec_is_null(seg, i)) continue;
            prod = wrap_mul_i64(prod, agg_read_i64(seg, i));
        }
    }
    return make_i64(prod);
}

static ray_t* agg_parted_minmax(ray_t* x, int want_max) {
    int8_t base = (int8_t)RAY_PARTED_BASETYPE(x->type);
    if (!agg_parted_numeric_base(base)) return ray_error("type", want_max ? "max expects a numeric or temporal parted column, got %s" : "min expects a numeric or temporal parted column, got %s", ray_type_name(base));
    ray_t** segs = (ray_t**)ray_data(x);
    int found = 0;
    double best_f = 0.0;
    int64_t best_i = 0;
    for (int64_t s = 0; s < x->len; s++) {
        ray_t* seg = segs[s];
        if (!seg) continue;
        int has_nulls = ray_vec_may_have_nulls(seg);
        if (base == RAY_F64 || base == RAY_F32) {
            for (int64_t i = 0; i < seg->len; i++) {
                if (has_nulls && ray_vec_is_null(seg, i)) continue;
                double v = base == RAY_F64
                    ? ((double*)ray_data(seg))[i]
                    : (double)((float*)ray_data(seg))[i];
                if (!found || (want_max ? v > best_f : v < best_f)) {
                    best_f = v; found = 1;
                }
            }
        } else {
            for (int64_t i = 0; i < seg->len; i++) {
                if (has_nulls && ray_vec_is_null(seg, i)) continue;
                int64_t v = agg_read_i64(seg, i);
                if (!found || (want_max ? v > best_i : v < best_i)) {
                    best_i = v; found = 1;
                }
            }
        }
    }
    if (!found) return ray_typed_null(-base);
    if (base == RAY_F64) return make_f64(best_f);
    if (base == RAY_F32) return ray_f32((float)best_f);
    return agg_atom_i64_for_type(base, best_i);
}

static int agg_numeric_flat_type(int8_t t) {
    return t == RAY_BOOL || t == RAY_U8 || t == RAY_I16 ||
           t == RAY_I32 || t == RAY_I64 || t == RAY_F32 || t == RAY_F64;
}

static int agg_read_vec_f64(ray_t* v, int64_t i, double* out) {
    void* d = ray_data(v);
    switch (v->type) {
    case RAY_F64: *out = ((double*)d)[i]; return 1;
    case RAY_F32: *out = (double)((float*)d)[i]; return 1;
    case RAY_I64: *out = (double)((int64_t*)d)[i]; return 1;
    case RAY_I32: *out = (double)((int32_t*)d)[i]; return 1;
    case RAY_I16: *out = (double)((int16_t*)d)[i]; return 1;
    case RAY_U8:
    case RAY_BOOL: *out = (double)((uint8_t*)d)[i]; return 1;
    default: return 0;
    }
}

static ray_t* agg_parted_truth(ray_t* x, int want_all) {
    int8_t base = (int8_t)RAY_PARTED_BASETYPE(x->type);
    if (!agg_numeric_flat_type(base))
        return ray_error("type", want_all ? "all expects a numeric parted column, got %s"
                                          : "any expects a numeric parted column, got %s",
                         ray_type_name(base));
    ray_t** segs = (ray_t**)ray_data(x);
    int64_t seen = 0, truthy = 0;
    for (int64_t s = 0; s < x->len; s++) {
        ray_t* seg = segs[s];
        if (!seg) continue;
        int has_nulls = ray_vec_may_have_nulls(seg);
        for (int64_t i = 0; i < seg->len; i++) {
            if (((i | s) & 65535) == 0 && ray_interrupted())
                return ray_error("cancel", "interrupted");
            if (has_nulls && ray_vec_is_null(seg, i)) continue;
            double v = 0.0;
            if (!agg_read_vec_f64(seg, i, &v)) continue;
            seen++;
            if (v != 0.0) truthy++;
        }
    }
    return ray_bool(want_all ? (truthy == seen) : (truthy > 0));
}

static ray_t* agg_truth_vec(ray_t* x, int want_all) {
    if (!ray_is_vec(x))
        return ray_error("type", want_all ? "all expects a numeric vector, got %s"
                                          : "any expects a numeric vector, got %s",
                         ray_type_name(x->type));
    if (!agg_numeric_flat_type(x->type))
        return ray_error("type", want_all ? "all expects a numeric vector, got %s"
                                          : "any expects a numeric vector, got %s",
                         ray_type_name(x->type));
    bool has_nulls = ray_vec_may_have_nulls(x);
    int64_t seen = 0, truthy = 0;
    for (int64_t i = 0; i < x->len; i++) {
        if ((i & 65535) == 0 && ray_interrupted())
            return ray_error("cancel", "interrupted");
        if (has_nulls && ray_vec_is_null(x, i)) continue;
        double v = 0.0;
        agg_read_vec_f64(x, i, &v);
        seen++;
        if (v != 0.0) truthy++;
    }
    return ray_bool(want_all ? (truthy == seen) : (truthy > 0));
}

static ray_t* agg_truth_list(ray_t* x, int want_all) {
    int64_t n = ray_len(x);
    int64_t seen = 0, truthy = 0;
    ray_t** elems = (ray_t**)ray_data(x);
    for (int64_t i = 0; i < n; i++) {
        if ((i & 65535) == 0 && ray_interrupted())
            return ray_error("cancel", "interrupted");
        if (!is_numeric(elems[i]))
            return ray_error("type", want_all ? "all: list elements must be numeric, got %s"
                                              : "any: list elements must be numeric, got %s",
                             ray_type_name(elems[i]->type));
        if (RAY_ATOM_IS_NULL(elems[i])) continue;
        seen++;
        if (as_f64(elems[i]) != 0.0) truthy++;
    }
    return ray_bool(want_all ? (truthy == seen) : (truthy > 0));
}

static ray_t* agg_pair_vec(ray_t* x, ray_t* y, uint16_t op) {
    const char* name = op == OP_COV ? "cov" :
                       op == OP_SCOV ? "scov" :
                       op == OP_WSUM ? "wsum" :
                       op == OP_WAVG ? "wavg" : "pearson_corr";
    if (!x || RAY_IS_ERR(x) || !y || RAY_IS_ERR(y))
        return ray_error("type", "%s: both arguments must be valid values", name);
    if (!ray_is_vec(x) || !ray_is_vec(y))
        return ray_error("type", "%s expects two numeric vectors, got %s and %s", name, ray_type_name(x->type), ray_type_name(y->type));
    if (x->len != y->len)
        return ray_error("length", "%s: vectors must have equal length, got %lld and %lld", name, (long long)x->len, (long long)y->len);
    if (!agg_numeric_flat_type(x->type) || !agg_numeric_flat_type(y->type))
        return ray_error("type", "%s expects numeric vectors, got %s and %s", name, ray_type_name(x->type), ray_type_name(y->type));

    bool xn = ray_vec_may_have_nulls(x);
    bool yn = ray_vec_may_have_nulls(y);
    int64_t cnt = 0;
    double sx = 0.0, sy = 0.0, sxx = 0.0, syy = 0.0, sxy = 0.0;
    for (int64_t i = 0; i < x->len; i++) {
        if ((i & 65535) == 0 && ray_interrupted())
            return ray_error("cancel", "interrupted");
        if ((xn && ray_vec_is_null(x, i)) || (yn && ray_vec_is_null(y, i)))
            continue;
        double xv = 0.0, yv = 0.0;
        agg_read_vec_f64(x, i, &xv);
        agg_read_vec_f64(y, i, &yv);
        sx += xv; sy += yv; sxx += xv * xv; syy += yv * yv;
        sxy += xv * yv;
        cnt++;
    }

    if (op == OP_WSUM) return ray_f64(ray_f64_fin(sxy));
    if (op == OP_WAVG) {
        if (cnt <= 0 || sx == 0.0) return ray_typed_null(-RAY_F64);
        return ray_f64(ray_f64_fin(sxy / sx));
    }
    if (op == OP_COV) {
        if (cnt <= 0) return ray_typed_null(-RAY_F64);
        double dn = (double)cnt;
        return ray_f64(ray_f64_fin((sxy - sx * sy / dn) / dn));
    }
    if (op == OP_SCOV) {
        if (cnt <= 1) return ray_typed_null(-RAY_F64);
        double dn = (double)cnt;
        return ray_f64(ray_f64_fin((sxy - sx * sy / dn) / (dn - 1.0)));
    }
    if (cnt < 2) return ray_typed_null(-RAY_F64);
    double dn = (double)cnt;
    double num = dn * sxy - sx * sy;
    double dx = dn * sxx - sx * sx;
    double dy = dn * syy - sy * sy;
    if (dx <= 0.0 || dy <= 0.0) return ray_typed_null(-RAY_F64);
    return ray_f64(ray_f64_fin(num / sqrt(dx * dy)));
}

ray_t* ray_sum_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_SUM);
    if (RAY_IS_PARTED(x->type)) return agg_parted_sum(x);
    if (ray_is_atom(x)) {
        /* u8/i16 scalar sum promotes to i64 */
        if (x->type == -RAY_U8)  return make_i64((int64_t)x->u8);
        if (x->type == -RAY_I16) return make_i64((int64_t)x->i16);
        ray_retain(x); return x;
    }
    if (ray_is_vec(x)) {
        /* Canonical admission: numeric + TIME (duration); DATE/TIMESTAMP are
         * absolute points and SYM/STR/GUID are non-numeric → type error. */
        if (!agg_type_admitted(OP_SUM, x->type)) return ray_error("type", "sum expects a numeric or time-duration vector, got %s", ray_type_name(x->type));
        /* Narrow/temporal types need specific return constructors that the
         * DAG executor doesn't provide — use scalar path for these.  TIMESTAMP
         * is rejected by agg_type_admitted() above, so only the duration-like
         * TIME and the narrow integer widths reach here.  Accumulation wraps
         * via wrap_add_i64 to stay UB-free (overflow needs a multi-GiB column
         * for the narrow types, but the wrap keeps the whole family uniform). */
        if (x->type == RAY_I32 || x->type == RAY_I16 || x->type == RAY_U8 ||
            x->type == RAY_TIME) {
            int64_t n = x->len;
            bool has_nulls = ray_vec_may_have_nulls(x);
            int64_t sum = 0;
            if (x->type == RAY_I32) {
                int32_t* d = (int32_t*)ray_data(x);
                if (has_nulls) { for (int64_t i = 0; i < n; i++) if (!ray_vec_is_null(x, i)) sum = wrap_add_i64(sum, d[i]); }
                else { for (int64_t i = 0; i < n; i++) sum = wrap_add_i64(sum, d[i]); }
                return make_i64(sum);
            } else if (x->type == RAY_I16) {
                int16_t* d = (int16_t*)ray_data(x);
                if (has_nulls) { for (int64_t i = 0; i < n; i++) if (!ray_vec_is_null(x, i)) sum = wrap_add_i64(sum, d[i]); }
                else { for (int64_t i = 0; i < n; i++) sum = wrap_add_i64(sum, d[i]); }
                return make_i64(sum);
            } else if (x->type == RAY_U8) {
                uint8_t* d = (uint8_t*)ray_data(x);
                if (has_nulls) { for (int64_t i = 0; i < n; i++) if (!ray_vec_is_null(x, i)) sum = wrap_add_i64(sum, d[i]); }
                else { for (int64_t i = 0; i < n; i++) sum = wrap_add_i64(sum, d[i]); }
                return make_i64(sum);
            } else {
                int32_t* d = (int32_t*)ray_data(x);
                if (has_nulls) { for (int64_t i = 0; i < n; i++) if (!ray_vec_is_null(x, i)) sum = wrap_add_i64(sum, d[i]); }
                else { for (int64_t i = 0; i < n; i++) sum = wrap_add_i64(sum, d[i]); }
                return ray_time(sum);
            }
        }
        /* I64/F64: parallel morsel-driven reduction via DAG executor */
        AGG_VEC_VIA_DAG(x, ray_sum);
    }
    if (!is_list(x)) return ray_error("type", "sum expects a numeric vector, atom, or list, got %s", ray_type_name(x->type));
    int64_t len = ray_len(x);
    if (len == 0) return make_i64(0);
    ray_t** elems = (ray_t**)ray_data(x);
    int has_float = 0;
    double fsum = 0.0;
    int64_t isum = 0;
    for (int64_t i = 0; i < len; i++) {
        if (!is_numeric(elems[i])) return ray_error("type", "sum: list elements must be numeric, got %s", ray_type_name(elems[i]->type));
        if (RAY_ATOM_IS_NULL(elems[i])) {
            if (elems[i]->type == -RAY_F64 || elems[i]->type == -RAY_F32) has_float = 1;
            continue;
        }
        if (elems[i]->type == -RAY_F64 || elems[i]->type == -RAY_F32) { has_float = 1; fsum += elems[i]->f64; }
        else {
            /* i64 atoms are read directly (exact above 2^53); other integer /
             * temporal atoms via as_f64.  Wrap-accumulate: signed overflow is
             * UB, and the typed-vector path already wraps. */
            int64_t v = (elems[i]->type == -RAY_I64) ? elems[i]->i64 : (int64_t)as_f64(elems[i]);
            isum = wrap_add_i64(isum, v);
            fsum += (double)v;
        }
    }
    return has_float ? make_f64(fsum) : make_i64(isum);
}

ray_t* ray_prod_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_PROD);
    if (RAY_IS_PARTED(x->type)) return agg_parted_prod(x);
    if (ray_is_atom(x)) { ray_retain(x); return x; }
    if (ray_is_vec(x)) {
        if (!agg_type_admitted(OP_PROD, x->type))
            return ray_error("type", "prod expects a numeric vector, got %s", ray_type_name(x->type));
        AGG_VEC_VIA_DAG(x, ray_prod);
    }
    if (!is_list(x)) return ray_error("type", "prod expects a numeric vector, atom, or list, got %s", ray_type_name(x->type));
    int64_t len = ray_len(x);
    if (len == 0) return make_i64(1);
    ray_t** elems = (ray_t**)ray_data(x);
    int has_float = 0;
    double fprod = 1.0;
    int64_t iprod = 1;
    for (int64_t i = 0; i < len; i++) {
        if (!is_numeric(elems[i]))
            return ray_error("type", "prod: list elements must be numeric, got %s", ray_type_name(elems[i]->type));
        if (RAY_ATOM_IS_NULL(elems[i])) {
            if (elems[i]->type == -RAY_F64 || elems[i]->type == -RAY_F32) has_float = 1;
            continue;
        }
        if (elems[i]->type == -RAY_F64 || elems[i]->type == -RAY_F32) {
            has_float = 1;
            fprod *= elems[i]->f64;
        } else {
            /* Read i64 directly: (int64_t)as_f64(atom) both loses precision
             * above 2^53 and is UB when the value rounds to >= 2^63.  Wrap-
             * multiply keeps overflow well-defined. */
            int64_t v = (elems[i]->type == -RAY_I64) ? elems[i]->i64 : (int64_t)as_f64(elems[i]);
            iprod = wrap_mul_i64(iprod, v);
            fprod *= (double)v;
        }
    }
    return has_float ? make_f64(fprod) : make_i64(iprod);
}

ray_t* ray_all_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_ALL);
    if (RAY_IS_PARTED(x->type)) return agg_parted_truth(x, 1);
    if (ray_is_atom(x)) {
        if (!is_numeric(x)) return ray_error("type", "all expects numeric values, got %s", ray_type_name(x->type));
        if (RAY_ATOM_IS_NULL(x)) return ray_bool(true);
        return ray_bool(as_f64(x) != 0.0);
    }
    if (is_list(x)) return agg_truth_list(x, 1);
    return agg_truth_vec(x, 1);
}

ray_t* ray_any_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_ANY);
    if (RAY_IS_PARTED(x->type)) return agg_parted_truth(x, 0);
    if (ray_is_atom(x)) {
        if (!is_numeric(x)) return ray_error("type", "any expects numeric values, got %s", ray_type_name(x->type));
        if (RAY_ATOM_IS_NULL(x)) return ray_bool(false);
        return ray_bool(as_f64(x) != 0.0);
    }
    if (is_list(x)) return agg_truth_list(x, 0);
    return agg_truth_vec(x, 0);
}

ray_t* ray_count_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_COUNT);
    if (x->type == RAY_TABLE) return make_i64(ray_table_nrows(x));
    if (x->type == RAY_DICT)  return make_i64(ray_dict_len(x));
    /* String atom: count = string length */
    if (ray_is_atom(x) && (-x->type) == RAY_STR)
        return make_i64((int64_t)ray_str_len(x));
    if (ray_is_vec(x))
        return make_i64(x->len);  /* count = total length including nulls */
    if (!is_list(x)) {
        /* Scalar atom → count 1 */
        if (ray_is_atom(x)) return make_i64(1);
        return ray_error("type", "count: unsupported type %s", ray_type_name(x->type));
    }
    return make_i64(ray_len(x));
}

ray_t* ray_avg_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_AVG);
    if (RAY_IS_PARTED(x->type)) return agg_parted_avg(x);
    if (ray_is_atom(x)) {
        if (RAY_ATOM_IS_NULL(x)) return ray_typed_null(-RAY_F64);
        if (is_numeric(x)) return make_f64(as_f64(x));
        ray_retain(x); return x;
    }
    if (ray_is_vec(x)) {
        /* Canonical admission: numeric + temporal (→ F64); SYM/STR/GUID are
         * non-numeric → type error (the DAG path otherwise averaged raw ids). */
        if (!agg_type_admitted(OP_AVG, x->type)) return ray_error("type", "avg expects a numeric or temporal vector, got %s", ray_type_name(x->type));
        AGG_VEC_VIA_DAG(x, ray_avg);
    }
    if (!is_list(x)) return ray_error("type", "avg expects a numeric vector, atom, or list, got %s", ray_type_name(x->type));
    int64_t len = ray_len(x);
    if (len == 0) return ray_error("domain", "avg: empty list has no average");
    ray_t** elems = (ray_t**)ray_data(x);
    double sum = 0.0;
    int64_t cnt = 0;
    for (int64_t i = 0; i < len; i++) {
        if (!is_numeric(elems[i])) return ray_error("type", "avg: list elements must be numeric, got %s", ray_type_name(elems[i]->type));
        if (RAY_ATOM_IS_NULL(elems[i])) continue;
        sum += as_f64(elems[i]); cnt++;
    }
    if (cnt == 0) return ray_typed_null(-RAY_F64);
    return make_f64(sum / (double)cnt);
}

ray_t* ray_min_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_MIN);
    if (RAY_IS_PARTED(x->type)) return agg_parted_minmax(x, 0);
    if (ray_is_atom(x)) { ray_retain(x); return x; }
    if (ray_is_vec(x)) {
        /* Per-chunk zone index fast path: O(n_chunks) instead of O(n_rows).
         * Only valid when the index was built for the column's current len
         * (mutation paths call ray_index_drop). */
        if (ray_index_kind(x) == RAY_IDX_CHUNK_ZONE) {
            ray_index_t* ix = ray_index_payload(x->index);
            if (ix->built_for_len == x->len) {
                uint32_t n_chunks = ix->u.chunk_zone.n_chunks;
                if (ix->u.chunk_zone.is_f64) {
                    const double* mins = (const double*)ray_data(ix->u.chunk_zone.mins);
                    double mn = INFINITY;
                    for (uint32_t g = 0; g < n_chunks; g++)
                        if (mins[g] < mn) mn = mins[g];
                    if (mn == INFINITY) return ray_typed_null(-RAY_F64);
                    return make_f64(mn);
                } else {
                    const int64_t* mins = (const int64_t*)ray_data(ix->u.chunk_zone.mins);
                    int64_t mn = INT64_MAX;
                    for (uint32_t g = 0; g < n_chunks; g++)
                        if (mins[g] < mn) mn = mins[g];
                    if (mn == INT64_MAX) return ray_typed_null(-x->type);
                    /* Preserve the column's storage width on the result. */
                    switch (x->type) {
                    case RAY_BOOL:      return ray_bool((bool)mn);
                    case RAY_U8:        return ray_u8((uint8_t)mn);
                    case RAY_I16:       return ray_i16((int16_t)mn);
                    case RAY_I32:       return ray_i32((int32_t)mn);
                    case RAY_DATE:      return ray_date((int32_t)mn);
                    case RAY_TIME:      return ray_time(mn);
                    case RAY_TIMESTAMP: return ray_timestamp(mn);
                    default:            return ray_i64(mn);
                    }
                }
            }
        }
        AGG_VEC_VIA_DAG(x, ray_min_op);
    }
    if (!is_list(x)) return ray_error("type", "min expects a vector, atom, or list, got %s", ray_type_name(x->type));
    int64_t len = ray_len(x);
    if (len == 0) return ray_error("domain", "min: empty list has no minimum");
    ray_t** elems = (ray_t**)ray_data(x);
    int has_float = 0, found = 0;
    double fmin = 0; int64_t imin = 0;
    for (int64_t i = 0; i < len; i++) {
        if (!is_numeric(elems[i])) return ray_error("type", "min: list elements must be numeric, got %s", ray_type_name(elems[i]->type));
        if (elems[i]->type == -RAY_F64 || elems[i]->type == -RAY_F32) has_float = 1;
        if (RAY_ATOM_IS_NULL(elems[i])) continue;
        double v = as_f64(elems[i]);
        if (!found || v < fmin) { fmin = v; imin = elems[i]->type == -RAY_I64 ? elems[i]->i64 : 0; found = 1; }
    }
    if (!found) return ray_typed_null(has_float ? -RAY_F64 : -RAY_I64);
    return has_float ? make_f64(fmin) : make_i64(imin);
}

ray_t* ray_max_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_MAX);
    if (RAY_IS_PARTED(x->type)) return agg_parted_minmax(x, 1);
    if (ray_is_atom(x)) { ray_retain(x); return x; }
    if (ray_is_vec(x)) {
        if (ray_index_kind(x) == RAY_IDX_CHUNK_ZONE) {
            ray_index_t* ix = ray_index_payload(x->index);
            if (ix->built_for_len == x->len) {
                uint32_t n_chunks = ix->u.chunk_zone.n_chunks;
                if (ix->u.chunk_zone.is_f64) {
                    const double* maxs = (const double*)ray_data(ix->u.chunk_zone.maxs);
                    double mx = -INFINITY;
                    for (uint32_t g = 0; g < n_chunks; g++)
                        if (maxs[g] > mx) mx = maxs[g];
                    if (mx == -INFINITY) return ray_typed_null(-RAY_F64);
                    return make_f64(mx);
                } else {
                    const int64_t* maxs = (const int64_t*)ray_data(ix->u.chunk_zone.maxs);
                    int64_t mx = INT64_MIN;
                    for (uint32_t g = 0; g < n_chunks; g++)
                        if (maxs[g] > mx) mx = maxs[g];
                    if (mx == INT64_MIN) return ray_typed_null(-x->type);
                    switch (x->type) {
                    case RAY_BOOL:      return ray_bool((bool)mx);
                    case RAY_U8:        return ray_u8((uint8_t)mx);
                    case RAY_I16:       return ray_i16((int16_t)mx);
                    case RAY_I32:       return ray_i32((int32_t)mx);
                    case RAY_DATE:      return ray_date((int32_t)mx);
                    case RAY_TIME:      return ray_time(mx);
                    case RAY_TIMESTAMP: return ray_timestamp(mx);
                    default:            return ray_i64(mx);
                    }
                }
            }
        }
        AGG_VEC_VIA_DAG(x, ray_max_op);
    }
    if (!is_list(x)) return ray_error("type", "max expects a vector, atom, or list, got %s", ray_type_name(x->type));
    int64_t len = ray_len(x);
    if (len == 0) return ray_error("domain", "max: empty list has no maximum");
    ray_t** elems = (ray_t**)ray_data(x);
    int has_float = 0, found = 0;
    double fmax = 0; int64_t imax = 0;
    for (int64_t i = 0; i < len; i++) {
        if (!is_numeric(elems[i])) return ray_error("type", "max: list elements must be numeric, got %s", ray_type_name(elems[i]->type));
        if (elems[i]->type == -RAY_F64 || elems[i]->type == -RAY_F32) has_float = 1;
        if (RAY_ATOM_IS_NULL(elems[i])) continue;
        double v = as_f64(elems[i]);
        if (!found || v > fmax) { fmax = v; imax = elems[i]->type == -RAY_I64 ? elems[i]->i64 : 0; found = 1; }
    }
    if (!found) return ray_typed_null(has_float ? -RAY_F64 : -RAY_I64);
    return has_float ? make_f64(fmax) : make_i64(imax);
}

ray_t* ray_first_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_FIRST);
    /* String first: return first char */
    if (ray_is_atom(x) && (-x->type) == RAY_STR) {
        size_t slen = ray_str_len(x);
        if (slen == 0) return ray_error("domain", "first: empty string has no first char");
        const char* p = ray_str_ptr(x);
        return ray_str(p, 1);
    }
    if (ray_is_atom(x)) { ray_retain(x); return x; }
    /* Table first: return first row as dict */
    if (x->type == RAY_TABLE) {
        if (ray_table_nrows(x) == 0) return ray_error("domain", "first: empty table has no first row");
        ray_t* idx = make_i64(0);
        ray_t* result = ray_at_fn(x, idx);
        ray_release(idx);
        return result;
    }
    if (ray_is_vec(x)) {
        if (ray_len(x) == 0) return ray_typed_null(-x->type);
        /* For non-I64/F64 types route through collection_elem which
         * preserves the element type.  The DAG path widens to i64 for
         * DATE/TIME/TIMESTAMP/BOOL/U8 — bypass it. */
        if (x->type == RAY_SYM   || x->type == RAY_I32  || x->type == RAY_I16 ||
            x->type == RAY_GUID  || x->type == RAY_STR  || x->type == RAY_BOOL ||
            x->type == RAY_U8    || x->type == RAY_DATE || x->type == RAY_TIME ||
            x->type == RAY_TIMESTAMP) {
            int alloc = 0;
            return collection_elem(x, 0, &alloc);
        }
        AGG_VEC_VIA_DAG(x, ray_first);
    }
    if (!is_list(x)) return ray_error("type", "first: unsupported type %s", ray_type_name(x->type));
    if (ray_len(x) == 0) return ray_typed_null(-RAY_I64);
    ray_t* elem = ((ray_t**)ray_data(x))[0];
    ray_retain(elem);
    return elem;
}

ray_t* ray_last_fn(ray_t* x) {
    if (ray_is_lazy(x)) return ray_lazy_append(x, OP_LAST);
    /* String last: return last char */
    if (ray_is_atom(x) && (-x->type) == RAY_STR) {
        size_t slen = ray_str_len(x);
        if (slen == 0) return ray_error("domain", "last: empty string has no last char");
        const char* p = ray_str_ptr(x);
        return ray_str(p + slen - 1, 1);
    }
    if (ray_is_atom(x)) { ray_retain(x); return x; }
    /* Table last: return last row as dict */
    if (x->type == RAY_TABLE) {
        int64_t nrows = ray_table_nrows(x);
        if (nrows == 0) return ray_error("domain", "last: empty table has no last row");
        ray_t* idx = make_i64(nrows - 1);
        ray_t* result = ray_at_fn(x, idx);
        ray_release(idx);
        return result;
    }
    if (ray_is_vec(x)) {
        if (ray_len(x) == 0) return ray_typed_null(-x->type);
        /* See ray_first_fn for rationale on the type whitelist. */
        if (x->type == RAY_SYM   || x->type == RAY_I32  || x->type == RAY_I16 ||
            x->type == RAY_GUID  || x->type == RAY_STR  || x->type == RAY_BOOL ||
            x->type == RAY_U8    || x->type == RAY_DATE || x->type == RAY_TIME ||
            x->type == RAY_TIMESTAMP) {
            int alloc = 0;
            return collection_elem(x, ray_len(x) - 1, &alloc);
        }
        AGG_VEC_VIA_DAG(x, ray_last);
    }
    if (!is_list(x)) return ray_error("type", "last: unsupported type %s", ray_type_name(x->type));
    int64_t len = ray_len(x);
    if (len == 0) return ray_typed_null(-RAY_I64);
    ray_t* elem = ((ray_t**)ray_data(x))[len - 1];
    ray_retain(elem);
    return elem;
}

/* Helper: copy non-null vec elements to double scratch buffer, compacted.
 * scratch->len is set to the number of non-null values copied.
 * Returns scratch ray_t* (caller must ray_release), or error. */
static ray_t* vec_to_f64_scratch(ray_t* x, double** out_vals) {
    int64_t len = ray_len(x);
    ray_t* scratch = ray_alloc(len * sizeof(double));
    if (!scratch) return ray_error("oom", NULL);
    scratch->type = RAY_F64;
    double* vals = (double*)ray_data(scratch);
    int64_t cnt = 0;
    if (x->type == RAY_I64) {
        int64_t* d = (int64_t*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = (double)d[i]; }
    } else if (x->type == RAY_F64) {
        double* d = (double*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = d[i]; }
    } else if (x->type == RAY_F32) {
        float* d = (float*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = (double)d[i]; }
    } else if (x->type == RAY_I32) {
        int32_t* d = (int32_t*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = (double)d[i]; }
    } else if (x->type == RAY_I16) {
        int16_t* d = (int16_t*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = (double)d[i]; }
    } else if (x->type == RAY_U8 || x->type == RAY_BOOL) {
        uint8_t* d = (uint8_t*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = (double)d[i]; }
    } else if (x->type == RAY_DATE || x->type == RAY_TIME) {
        /* temporal stored as int32 days/ms — avg/var/stddev compute over the
         * raw counts (result F64), per the canonical admission table. */
        int32_t* d = (int32_t*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = (double)d[i]; }
    } else if (x->type == RAY_TIMESTAMP) {
        int64_t* d = (int64_t*)ray_data(x);
        for (int64_t i = 0; i < len; i++) { if (!ray_vec_is_null(x, i)) vals[cnt++] = (double)d[i]; }
    } else {
        ray_release(scratch);
        return ray_error("type", "expects a numeric or temporal vector, got %s", ray_type_name(x->type));
    }
    scratch->len = cnt;
    *out_vals = vals;
    return scratch;
}

ray_t* ray_med_fn(ray_t* x) {
    /* The dispatcher always materialises non-LAZY_AWARE fn args, so x
     * is already concrete here. */
    if (RAY_IS_ERR(x)) return x;
    /* Scalar: median of single value → f64 */
    if (ray_is_atom(x)) {
        if (RAY_ATOM_IS_NULL(x)) return ray_typed_null(-RAY_F64);
        if (is_numeric(x)) return make_f64(as_f64(x));
        return ray_error("type", "med expects a numeric atom, got %s", ray_type_name(x->type));
    }
    int64_t len;
    ray_t* scratch = NULL;
    double* vals = NULL;

    if (ray_is_vec(x)) {
        len = ray_len(x);
        if (len == 0) return ray_typed_null(-RAY_F64);
        scratch = vec_to_f64_scratch(x, &vals);
        if (RAY_IS_ERR(scratch)) return scratch;
    } else if (is_list(x)) {
        len = ray_len(x);
        if (len == 0) return ray_typed_null(-RAY_F64);
        ray_t** elems = (ray_t**)ray_data(x);
        scratch = ray_alloc(len * sizeof(double));
        if (!scratch) return ray_error("oom", NULL);
        scratch->type = RAY_F64;
        scratch->len = 0;
        vals = (double*)ray_data(scratch);
        int64_t cnt_l = 0;
        for (int64_t i = 0; i < len; i++) {
            if (ray_is_atom(elems[i]) && RAY_ATOM_IS_NULL(elems[i])) continue;
            if (!is_numeric(elems[i])) { ray_release(scratch); return ray_error("type", "med: list elements must be numeric, got %s", ray_type_name(elems[i]->type)); }
            vals[cnt_l++] = as_f64(elems[i]);
        }
        scratch->len = cnt_l;
    } else {
        return ray_error("type", "med expects a numeric atom, vector, or list, got %s", ray_type_name(x->type));
    }

    /* scratch->len holds the count of non-null values (already compacted) */
    int64_t cnt = scratch->len;
    if (cnt == 0) { ray_release(scratch); return ray_typed_null(-RAY_F64); }

    /* O(n) average partial-sort.  Two-call quantile-interpolator
     * pattern: for odd n one nth_element places the middle; for even
     * n a second nth_element on the right half locates the upper
     * middle.  Replaces an O(n^2) insertion sort that hung for
     * groups larger than ~10k. */
    int64_t k = cnt / 2;
    double median;
    if (cnt % 2 == 1) {
        nth_element_dbl(vals, 0, cnt - 1, k);
        median = vals[k];
    } else {
        nth_element_dbl(vals, 0, cnt - 1, k - 1);
        nth_element_dbl(vals, k, cnt - 1, k);
        median = (vals[k - 1] + vals[k]) / 2.0;
    }
    ray_release(scratch);
    return make_f64(median);
}

ray_t* ray_mode_fn(ray_t* x) {
    if (RAY_IS_ERR(x)) return x;
    if (ray_is_atom(x)) {
        ray_retain(x);
        return x;
    }
    if (!ray_is_vec(x) && !is_list(x))
        return ray_error("type", "mode expects an atom, vector, or list, got %s", ray_type_name(x->type));
    if (ray_len(x) == 0) {
        int8_t nt = ray_is_vec(x) ? (int8_t)(-x->type) : (int8_t)(-RAY_I64);
        return ray_typed_null(nt);
    }

    ray_t* groups = ray_group_indices_fn(x);
    if (!groups || RAY_IS_ERR(groups))
        return groups ? groups : ray_error("oom", NULL);

    ray_t* keys = ray_dict_keys(groups);
    ray_t* vals = ray_dict_vals(groups);
    if (!keys || !vals || vals->type != RAY_LIST) {
        ray_release(groups);
        return ray_error("type", "mode: failed to group input");
    }

    int64_t best = -1;
    int64_t best_count = -1;
    ray_t** idx_vecs = (ray_t**)ray_data(vals);
    for (int64_t i = 0; i < ray_len(vals); i++) {
        bool is_null_key = false;
        if (keys->type == RAY_LIST) {
            ray_t* k = ((ray_t**)ray_data(keys))[i];
            is_null_key = ray_is_atom(k) && RAY_ATOM_IS_NULL(k);
        } else {
            is_null_key = ray_vec_is_null(keys, i);
        }
        if (is_null_key) continue;
        int64_t cnt = idx_vecs[i] ? ray_len(idx_vecs[i]) : 0;
        if (cnt > best_count) {
            best = i;
            best_count = cnt;
        }
    }

    if (best < 0) {
        ray_release(groups);
        int8_t nt = ray_is_vec(x) ? (int8_t)(-x->type) : (int8_t)(-RAY_I64);
        return ray_typed_null(nt);
    }

    int alloc = 0;
    ray_t* out = collection_elem(keys, best, &alloc);
    if (!out || RAY_IS_ERR(out)) {
        ray_release(groups);
        return out ? out : ray_error("oom", NULL);
    }
    if (!alloc) ray_retain(out);
    ray_release(groups);
    return out;
}

static ray_t* quantile_prob_arg(ray_t* q_obj, double scale, const char* name,
                                double* out_q) {
    if (!q_obj || !ray_is_atom(q_obj) || !is_numeric(q_obj))
        return ray_error("type", "%s: probability must be a numeric atom", name);
    if (RAY_ATOM_IS_NULL(q_obj))
        return ray_error("domain", "%s: probability must be non-null", name);
    double raw = as_f64(q_obj);
    if (!__builtin_isfinite(raw))
        return ray_error("domain", "%s: probability must be finite", name);
    if (raw < 0.0 || raw > scale)
        return ray_error("domain", "%s: probability out of range", name);
    *out_q = raw / scale;
    return NULL;
}

double ray_nth_dbl_inplace(double* a, int64_t n, int64_t k) {
    if (!a || n <= 0 || k < 0 || k >= n) return NULL_F64;
    nth_element_dbl(a, 0, n - 1, k);
    return a[k];
}

double ray_quantile_dbl_inplace(double* a, int64_t n, double q) {
    if (n <= 0) return 0.0;
    if (n == 1) return a[0];
    if (q <= 0.0) {
        nth_element_dbl(a, 0, n - 1, 0);
        return a[0];
    }
    if (q >= 1.0) {
        nth_element_dbl(a, 0, n - 1, n - 1);
        return a[n - 1];
    }
    double pos = q * (double)(n - 1);
    int64_t lo = (int64_t)pos;
    double frac = pos - (double)lo;
    if (frac <= 0.0) {
        nth_element_dbl(a, 0, n - 1, lo);
        return a[lo];
    }
    int64_t hi = lo + 1;
    nth_element_dbl(a, 0, n - 1, lo);
    double lower = a[lo];
    nth_element_dbl(a, hi, n - 1, hi);
    double upper = a[hi];
    return lower + frac * (upper - lower);
}

static ray_t* quantile_core(ray_t* x, double q, const char* name) {
    if (RAY_IS_ERR(x)) return x;
    if (ray_is_atom(x)) {
        if (RAY_ATOM_IS_NULL(x)) return ray_typed_null(-RAY_F64);
        if (is_numeric(x)) return make_f64(as_f64(x));
        return ray_error("type", "%s expects a numeric atom, got %s", name, ray_type_name(x->type));
    }

    int64_t len;
    ray_t* scratch = NULL;
    double* vals = NULL;

    if (ray_is_vec(x)) {
        len = ray_len(x);
        if (len == 0) return ray_typed_null(-RAY_F64);
        scratch = vec_to_f64_scratch(x, &vals);
        if (RAY_IS_ERR(scratch)) return scratch;
    } else if (is_list(x)) {
        len = ray_len(x);
        if (len == 0) return ray_typed_null(-RAY_F64);
        ray_t** elems = (ray_t**)ray_data(x);
        scratch = ray_alloc(len * sizeof(double));
        if (!scratch) return ray_error("oom", NULL);
        scratch->type = RAY_F64;
        scratch->len = 0;
        vals = (double*)ray_data(scratch);
        int64_t cnt_l = 0;
        for (int64_t i = 0; i < len; i++) {
            if (ray_is_atom(elems[i]) && RAY_ATOM_IS_NULL(elems[i])) continue;
            if (!is_numeric(elems[i])) {
                ray_release(scratch);
                return ray_error("type", "%s: list elements must be numeric, got %s", name, ray_type_name(elems[i]->type));
            }
            vals[cnt_l++] = as_f64(elems[i]);
        }
        scratch->len = cnt_l;
    } else {
        return ray_error("type", "%s expects a numeric atom, vector, or list, got %s", name, ray_type_name(x->type));
    }

    int64_t cnt = scratch->len;
    if (cnt == 0) {
        ray_release(scratch);
        return ray_typed_null(-RAY_F64);
    }
    double v = ray_quantile_dbl_inplace(vals, cnt, q);
    ray_release(scratch);
    return make_f64(v);
}

ray_t* ray_quantile_fn(ray_t* x, ray_t* q_obj) {
    double q = 0.0;
    ray_t* err = quantile_prob_arg(q_obj, 1.0, "quantile", &q);
    if (err) return err;
    return quantile_core(x, q, "quantile");
}

ray_t* ray_percentile_fn(ray_t* x, ray_t* p_obj) {
    double q = 0.0;
    ray_t* err = quantile_prob_arg(p_obj, 100.0, "percentile", &q);
    if (err) return err;
    return quantile_core(x, q, "percentile");
}

static ray_t* var_stddev_core(ray_t* x, int sample, int take_sqrt);


/* In-place exact median over a flat double buffer.  Caller owns the
 * buffer; we permute its elements via nth_element_dbl.  Returns NaN
 * if n <= 0 (caller must filter that case if a typed-null is needed).
 *
 * Used by the per-group median fast path in query.c which avoids the
 * full ray_med_fn slice-allocation cost — see aggr_med_per_group_buf. */
double ray_median_dbl_inplace(double* a, int64_t n) {
    if (n <= 0) return 0.0;
    if (n == 1) return a[0];
    int64_t k = n / 2;
    if (n % 2 == 1) {
        nth_element_dbl(a, 0, n - 1, k);
        return a[k];
    }
    nth_element_dbl(a, 0, n - 1, k - 1);
    nth_element_dbl(a, k, n - 1, k);
    return (a[k - 1] + a[k]) / 2.0;
}


ray_t* ray_dev_fn(ray_t* x) { return var_stddev_core(x, 0, 1); }

/* Shared core for variance / stddev in sample or population mode.
 * sample=1 -> divide sum-of-squares by (n-1); sample=0 -> divide by n.
 * take_sqrt=1 -> stddev; take_sqrt=0 -> variance. */
static ray_t* var_stddev_core(ray_t* x, int sample, int take_sqrt) {
    /* The dispatcher always materialises non-LAZY_AWARE fn args, so x
     * is already concrete here. */
    if (RAY_IS_ERR(x)) return x;
    if (ray_is_atom(x)) {
        if (RAY_ATOM_IS_NULL(x)) return ray_typed_null(-RAY_F64);
        if (is_numeric(x)) return sample ? ray_typed_null(-RAY_F64) : make_f64(0.0);
        return ray_error("type", "var/stddev expects a numeric atom, got %s", ray_type_name(x->type));
    }

    double* vals = NULL;
    ray_t*  scratch = NULL;
    int64_t cnt = 0;

    if (ray_is_vec(x)) {
        if (ray_len(x) == 0) return ray_typed_null(-RAY_F64);
        scratch = vec_to_f64_scratch(x, &vals);
        if (RAY_IS_ERR(scratch)) return scratch;
        cnt = scratch->len;
    } else if (is_list(x)) {
        int64_t len = ray_len(x);
        if (len == 0) return ray_typed_null(-RAY_F64);
        ray_t** elems = (ray_t**)ray_data(x);
        /* Use a fresh f64 vec as a scratch buffer so we reuse the vec path's cleanup. */
        scratch = ray_vec_new(RAY_F64, len);
        if (RAY_IS_ERR(scratch)) return scratch;
        vals = (double*)ray_data(scratch);
        for (int64_t i = 0; i < len; i++) {
            if (!is_numeric(elems[i])) { ray_release(scratch); return ray_error("type", "var/stddev: list elements must be numeric, got %s", ray_type_name(elems[i]->type)); }
            if (!RAY_ATOM_IS_NULL(elems[i])) vals[cnt++] = as_f64(elems[i]);
        }
        scratch->len = cnt;
    } else {
        return ray_error("type", "var/stddev expects a numeric atom, vector, or list, got %s", ray_type_name(x->type));
    }

    if (cnt == 0 || (sample && cnt <= 1)) {
        ray_release(scratch);
        return ray_typed_null(-RAY_F64);
    }

    double sum = 0.0;
    for (int64_t i = 0; i < cnt; i++) sum += vals[i];
    double mean = sum / (double)cnt;
    double sqdiff = 0.0;
    for (int64_t i = 0; i < cnt; i++) { double d = vals[i] - mean; sqdiff += d * d; }
    ray_release(scratch);
    double divisor = sample ? (double)(cnt - 1) : (double)cnt;
    double v = sqdiff / divisor;
    return make_f64(take_sqrt ? sqrt(v) : v);
}

ray_t* ray_stddev_fn(ray_t* x)     { return var_stddev_core(x, 1, 1); }
ray_t* ray_stddev_pop_fn(ray_t* x) { return var_stddev_core(x, 0, 1); }
ray_t* ray_var_fn(ray_t* x)        { return var_stddev_core(x, 1, 0); }
ray_t* ray_var_pop_fn(ray_t* x)    { return var_stddev_core(x, 0, 0); }

/* (pearson_corr x y) — Pearson correlation coefficient between two
 * numeric vectors of equal length.  Single-pass formulation:
 *
 *   r = (n·Σxy − Σx·Σy) / sqrt((n·Σx² − Σx²)(n·Σy² − Σy²))
 *
 * Returns F64 in [-1.0, 1.0], NaN when either side has zero variance
 * (constant column) or when n < 2 (correlation undefined).  Type-
 * coerces narrow ints / temporal types to F64 via as_f64 so the
 * single fp accumulator handles every numeric column type.  Nulls in
 * either vector skip the row from BOTH sums (pairwise complete-case
 * deletion, the conventional pearson-correlation default).
 *
 * Per-group usage: routed through the eval-level scatter — the
 * planner's expr_refs_row_column sees x and y as column refs, the
 * non-agg full-table eval collapses the call to a scalar, and the
 * non-row-aligned fallback re-runs the call on each group's slice. */
ray_t* ray_pearson_corr_fn(ray_t* x, ray_t* y) {
    return agg_pair_vec(x, y, OP_PEARSON_CORR);
}

ray_t* ray_cov_fn(ray_t* x, ray_t* y)  { return agg_pair_vec(x, y, OP_COV); }
ray_t* ray_scov_fn(ray_t* x, ray_t* y) { return agg_pair_vec(x, y, OP_SCOV); }
ray_t* ray_wsum_fn(ray_t* x, ray_t* y) { return agg_pair_vec(x, y, OP_WSUM); }
ray_t* ray_wavg_fn(ray_t* x, ray_t* y) { return agg_pair_vec(x, y, OP_WAVG); }