teeny-kernels 0.2.0

/*
 * Copyright (c) 2026 Teenygrad.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#![allow(non_snake_case)]

use teeny_macros::kernel;
use teeny_triton::triton::{
    types::{AddOffsets, Comparison},
    *,
};

/// NAdam step (Nesterov-accelerated Adam).
///
/// All bias correction terms and Nesterov coefficients are precomputed on the
/// host and passed as scalars:
///
/// ```text
/// exp_avg    = beta1 * exp_avg    + (1 - beta1) * g
/// exp_avg_sq = beta2 * exp_avg_sq + (1 - beta2) * g²
/// denom      = sqrt(exp_avg_sq) / bias_corr2_sqrt + eps
/// p         -= lr * (coeff_g * g + coeff_m * exp_avg) / denom
/// ```
///
/// Precomputed on host:
/// - `bias_corr2_sqrt = sqrt(1 - beta2^t)`
/// - `coeff_g  = (1 - mu_t)  / (1 - mu_product)`  (grad contribution)
/// - `coeff_m  = mu_t1       / (1 - mu_product_next)` (moment contribution)
///
/// Grid: `[ceil(n_elements / BLOCK_SIZE), 1, 1]`.
#[kernel]
pub fn nadam_step<T: Triton, const BLOCK_SIZE: i32>(
    params_ptr: T::Pointer<f32>,
    grad_ptr: T::Pointer<f32>,
    exp_avg_ptr: T::Pointer<f32>,
    exp_avg_sq_ptr: T::Pointer<f32>,
    n_elements: i32,
    lr: f32,
    beta1: f32,
    beta2: f32,
    eps: f32,
    weight_decay: f32,
    bias_corr2_sqrt: f32,
    coeff_g: f32,
    coeff_m: f32,
) where
    T::I32Tensor: types::Tensor<i32, 1>,
    T::I32Tensor: Comparison<i32, BoolTensor = T::BoolTensor>,
    T::Pointer<f32>: AddOffsets<i32, 1, T::I32Tensor, Output = T::Tensor<T::Pointer<f32>>>,
{
    let pid = T::program_id(Axis::X);
    let block_start = pid * BLOCK_SIZE;
    let offsets = T::arange(0, BLOCK_SIZE) + block_start;
    let mask = offsets.lt(n_elements);

    let p = T::load(
        params_ptr.add_offsets(offsets),
        Some(mask),
        None,
        &[],
        None,
        None,
        None,
        false,
    );
    let g = T::load(
        grad_ptr.add_offsets(offsets),
        Some(mask),
        None,
        &[],
        None,
        None,
        None,
        false,
    );
    let exp_avg = T::load(
        exp_avg_ptr.add_offsets(offsets),
        Some(mask),
        None,
        &[],
        None,
        None,
        None,
        false,
    );
    let exp_avg_sq = T::load(
        exp_avg_sq_ptr.add_offsets(offsets),
        Some(mask),
        None,
        &[],
        None,
        None,
        None,
        false,
    );

    let beta1_t = T::full(&[BLOCK_SIZE], beta1);
    let beta2_t = T::full(&[BLOCK_SIZE], beta2);
    let one_m_beta1 = T::full(&[BLOCK_SIZE], 1.0_f32 - beta1);
    let one_m_beta2 = T::full(&[BLOCK_SIZE], 1.0_f32 - beta2);
    let eps_t = T::full(&[BLOCK_SIZE], eps);
    let lr_t = T::full(&[BLOCK_SIZE], lr);
    let bc2sqrt_t = T::full(&[BLOCK_SIZE], bias_corr2_sqrt);
    let cg_t = T::full(&[BLOCK_SIZE], coeff_g);
    let cm_t = T::full(&[BLOCK_SIZE], coeff_m);
    let wd_t = T::full(&[BLOCK_SIZE], weight_decay);

    let g_eff = g + wd_t * p;

    let exp_avg_new = beta1_t * exp_avg + one_m_beta1 * g_eff;
    let exp_avg_sq_new = beta2_t * exp_avg_sq + one_m_beta2 * g_eff * g_eff;

    let denom = T::sqrt_rn(exp_avg_sq_new) / bc2sqrt_t + eps_t;
    let p_new = p - lr_t * (cg_t * g_eff + cm_t * exp_avg_new) / denom;

    T::store(
        params_ptr.add_offsets(offsets),
        p_new,
        Some(mask),
        &[],
        None,
        None,
    );
    T::store(
        exp_avg_ptr.add_offsets(offsets),
        exp_avg_new,
        Some(mask),
        &[],
        None,
        None,
    );
    T::store(
        exp_avg_sq_ptr.add_offsets(offsets),
        exp_avg_sq_new,
        Some(mask),
        &[],
        None,
        None,
    );
}