mincdc 0.1.0

A very simple yet efficient content-defined chunking algorithm.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301

use std::arch::x86_64::*;
use std::sync::LazyLock;

use crate::scalar;

const PREFETCH_DIST: usize = 16384;

// The avx512_impl, avx2_impl or sse41_impl finds a position which has the
// global minimizer within the next four bytes.

/// # Safety
/// AVX-512F must be available.
#[target_feature(enable = "avx512f")]
unsafe fn avx512_impl<const SHOULD_HASH: bool>(
    bytes: &[u8],
    multiplier: u32,
    addend: u32,
) -> usize {
    if bytes.len() < 64 + 3 {
        return unsafe { avx2_impl::<SHOULD_HASH>(bytes, multiplier, addend) };
    }

    let vmul = _mm512_set1_epi32(multiplier as i32);
    let vadd = _mm512_set1_epi32(addend as i32);
    let mut accum_lo = _mm512_set1_epi64(u64::MAX as i64);
    let mut accum_hi = _mm512_set1_epi64(u64::MAX as i64);

    let mut offset = 0;
    unsafe {
        while offset + 4 <= bytes.len() {
            if offset + 64 + 3 > bytes.len() {
                offset = bytes.len() - 64 - 3;
            }

            _mm_prefetch::<_MM_HINT_T0>(bytes.as_ptr().add(offset + PREFETCH_DIST).cast());

            let mut v0 = _mm512_loadu_si512(bytes.as_ptr().add(offset).cast());
            let mut v1 = _mm512_loadu_si512(bytes.as_ptr().add(offset + 1).cast());
            let mut v2 = _mm512_loadu_si512(bytes.as_ptr().add(offset + 2).cast());
            let mut v3 = _mm512_loadu_si512(bytes.as_ptr().add(offset + 3).cast());

            if SHOULD_HASH {
                v0 = _mm512_mullo_epi32(v0, vmul);
                v1 = _mm512_mullo_epi32(v1, vmul);
                v2 = _mm512_mullo_epi32(v2, vmul);
                v3 = _mm512_mullo_epi32(v3, vmul);
                v0 = _mm512_add_epi32(v0, vadd);
                v1 = _mm512_add_epi32(v1, vadd);
                v2 = _mm512_add_epi32(v2, vadd);
                v3 = _mm512_add_epi32(v3, vadd);
            }

            let m01 = _mm512_min_epu32(v0, v1);
            let m23 = _mm512_min_epu32(v2, v3);
            let m0123 = _mm512_min_epu32(m01, m23);

            // We use the 64-bit minimum to compute the (val, offset) argmin
            // by interleaving values and offsets.
            let voffset = _mm512_set1_epi32(offset as i32);
            let pairs_lo = _mm512_unpacklo_epi32(voffset, m0123);
            let pairs_hi = _mm512_unpackhi_epi32(voffset, m0123);
            accum_lo = _mm512_min_epu64(accum_lo, pairs_lo);
            accum_hi = _mm512_min_epu64(accum_hi, pairs_hi);
            offset += 64;
        }

        // Add the corresponding relative offsets for each 64-bit subregister.
        static SUBREG_OFFSET_LO: [u64; 8] = [0, 4, 16, 20, 32, 36, 48, 52];
        static SUBREG_OFFSET_HI: [u64; 8] = [8, 12, 24, 28, 40, 44, 56, 60];
        accum_lo = _mm512_add_epi64(
            accum_lo,
            _mm512_loadu_epi64(SUBREG_OFFSET_LO.as_ptr().cast()),
        );
        accum_hi = _mm512_add_epi64(
            accum_hi,
            _mm512_loadu_epi64(SUBREG_OFFSET_HI.as_ptr().cast()),
        );
        accum_lo = _mm512_min_epu64(accum_lo, accum_hi);

        let mut out = [0u64; 8];
        _mm512_storeu_si512(out.as_mut_ptr().cast(), accum_lo);
        out.iter().copied().min().unwrap() as u32 as usize
    }
}

/// # Safety
/// AVX2 must be available.
#[target_feature(enable = "avx2")]
unsafe fn avx2_impl<const SHOULD_HASH: bool>(bytes: &[u8], multiplier: u32, addend: u32) -> usize {
    if bytes.len() < 32 + 3 {
        return sse41_impl::<SHOULD_HASH>(bytes, multiplier, addend);
    }

    // AVX2 has no unsigned comparison so add i32::MIN, shifting 0 to i32::MIN.
    let vmul = _mm256_set1_epi32(multiplier as i32);
    let vadd = _mm256_set1_epi32((addend as i32).wrapping_add(i32::MIN));

    let mut offset = 0;
    let mut min_val = _mm256_set1_epi32(i32::MAX);
    let mut min_offset = _mm256_set1_epi32(0);

    let mut body = |offset: &mut usize| unsafe {
        let mut v0 = _mm256_loadu_si256(bytes.as_ptr().add(*offset).cast());
        let mut v1 = _mm256_loadu_si256(bytes.as_ptr().add(*offset + 1).cast());
        let mut v2 = _mm256_loadu_si256(bytes.as_ptr().add(*offset + 2).cast());
        let mut v3 = _mm256_loadu_si256(bytes.as_ptr().add(*offset + 3).cast());

        let m0123s;
        if SHOULD_HASH {
            // We fused the unsigned -> signed conversion into the adds here.
            v0 = _mm256_mullo_epi32(v0, vmul);
            v1 = _mm256_mullo_epi32(v1, vmul);
            v2 = _mm256_mullo_epi32(v2, vmul);
            v3 = _mm256_mullo_epi32(v3, vmul);
            v0 = _mm256_add_epi32(v0, vadd);
            v1 = _mm256_add_epi32(v1, vadd);
            v2 = _mm256_add_epi32(v2, vadd);
            v3 = _mm256_add_epi32(v3, vadd);
            let m01s = _mm256_min_epi32(v0, v1);
            let m23s = _mm256_min_epi32(v2, v3);
            m0123s = _mm256_min_epi32(m01s, m23s);
        } else {
            // We do a single conversion here after computing the unsigned minimum.
            let m01u = _mm256_min_epu32(v0, v1);
            let m23u = _mm256_min_epu32(v2, v3);
            let m0123u = _mm256_min_epu32(m01u, m23u);
            m0123s = _mm256_add_epi32(m0123u, _mm256_set1_epi32(i32::MIN));
        }

        let voffset = _mm256_set1_epi32(*offset as i32);
        let better = _mm256_cmpgt_epi32(min_val, m0123s);
        min_val = _mm256_min_epi32(min_val, m0123s);
        min_offset = _mm256_blendv_epi8(min_offset, voffset, better);
        *offset += 32;
    };

    unsafe {
        while offset + 64 + 4 <= bytes.len() {
            _mm_prefetch::<_MM_HINT_T0>(bytes.as_ptr().add(offset + PREFETCH_DIST).cast());

            // Manually unrolled twice.
            body(&mut offset);
            body(&mut offset);
        }
        while offset + 4 <= bytes.len() {
            if offset + 32 + 3 > bytes.len() {
                offset = bytes.len() - 32 - 3;
            }

            body(&mut offset);
        }

        // Add the corresponding relative offsets for each 32-bit subregister
        // and interleave to 64-bit (value, offset) pairs.
        static SUBREG_OFFSET: [u32; 8] = [0, 4, 8, 12, 16, 20, 24, 28];
        min_offset = _mm256_add_epi32(
            min_offset,
            _mm256_loadu_si256(SUBREG_OFFSET.as_ptr().cast()),
        );
        let pairs_lo = _mm256_unpacklo_epi32(min_offset, min_val);
        let pairs_hi = _mm256_unpackhi_epi32(min_offset, min_val);

        let mut out = [0i64; 8];
        _mm256_storeu_si256(out.as_mut_ptr().cast(), pairs_lo);
        _mm256_storeu_si256(out.as_mut_ptr().add(4).cast(), pairs_hi);
        out.iter().copied().min().unwrap() as u32 as usize
    }
}

/// # Safety
/// SSE4.1 must be available.
#[target_feature(enable = "sse4.1")]
fn sse41_impl<const SHOULD_HASH: bool>(bytes: &[u8], multiplier: u32, addend: u32) -> usize {
    if bytes.len() < 16 + 3 {
        return scalar::argmin_u32_overlapping_hashed::<SHOULD_HASH>(bytes, multiplier, addend);
    }

    // SSE2 has no unsigned comparison so add i32::MIN, shifting 0 to i32::MIN.
    let vmul = _mm_set1_epi32(multiplier as i32);
    let vadd = _mm_set1_epi32((addend as i32).wrapping_add(i32::MIN));

    let mut offset = 0;
    let mut min_val = _mm_set1_epi32(i32::MAX);
    let mut min_offset = _mm_set1_epi32(0);

    let mut body = |offset: &mut usize| unsafe {
        let mut v0 = _mm_loadu_si128(bytes.as_ptr().add(*offset).cast());
        let mut v1 = _mm_loadu_si128(bytes.as_ptr().add(*offset + 1).cast());
        let mut v2 = _mm_loadu_si128(bytes.as_ptr().add(*offset + 2).cast());
        let mut v3 = _mm_loadu_si128(bytes.as_ptr().add(*offset + 3).cast());

        let m0123s;
        if SHOULD_HASH {
            // We fused the unsigned -> signed conversion into the adds here.
            v0 = _mm_mullo_epi32(v0, vmul);
            v1 = _mm_mullo_epi32(v1, vmul);
            v2 = _mm_mullo_epi32(v2, vmul);
            v3 = _mm_mullo_epi32(v3, vmul);
            v0 = _mm_add_epi32(v0, vadd);
            v1 = _mm_add_epi32(v1, vadd);
            v2 = _mm_add_epi32(v2, vadd);
            v3 = _mm_add_epi32(v3, vadd);
            let m01s = _mm_min_epi32(v0, v1);
            let m23s = _mm_min_epi32(v2, v3);
            m0123s = _mm_min_epi32(m01s, m23s);
        } else {
            // We do a single conversion here after computing the unsigned minimum.
            let m01u = _mm_min_epu32(v0, v1);
            let m23u = _mm_min_epu32(v2, v3);
            let m0123u = _mm_min_epu32(m01u, m23u);
            m0123s = _mm_add_epi32(m0123u, _mm_set1_epi32(i32::MIN));
        }

        let voffset = _mm_set1_epi32(*offset as i32);
        let better = _mm_cmpgt_epi32(min_val, m0123s);
        min_val = _mm_min_epi32(min_val, m0123s);
        min_offset = _mm_blendv_epi8(min_offset, voffset, better);
        *offset += 16;
    };

    unsafe {
        while offset + 32 + 4 <= bytes.len() {
            _mm_prefetch::<_MM_HINT_T0>(bytes.as_ptr().add(offset + PREFETCH_DIST).cast());

            // Manually unrolled twice.
            body(&mut offset);
            body(&mut offset);
        }
        while offset + 4 <= bytes.len() {
            if offset + 16 + 3 > bytes.len() {
                offset = bytes.len() - 16 - 3;
            }

            body(&mut offset);
        }

        // Add the corresponding relative offsets for each 32-bit subregister
        // and interleave to 64-bit (value, offset) pairs.
        static SUBREG_OFFSET: [u32; 4] = [0, 4, 8, 12];
        min_offset = _mm_add_epi32(min_offset, _mm_loadu_si128(SUBREG_OFFSET.as_ptr().cast()));
        let pairs_lo = _mm_unpacklo_epi32(min_offset, min_val);
        let pairs_hi = _mm_unpackhi_epi32(min_offset, min_val);

        let mut out = [0i64; 4];
        _mm_storeu_si128(out.as_mut_ptr().cast(), pairs_lo);
        _mm_storeu_si128(out.as_mut_ptr().add(2).cast(), pairs_hi);
        out.iter().copied().min().unwrap() as u32 as usize
    }
}

type ArgMinFn = unsafe fn(&[u8], u32, u32) -> usize;

static ARGMIN_IMPL: LazyLock<ArgMinFn> = LazyLock::new(|| {
    if is_x86_feature_detected!("avx512f") {
        avx512_impl::<false>
    } else if is_x86_feature_detected!("avx2") {
        avx2_impl::<false>
    } else if is_x86_feature_detected!("sse4.1") {
        sse41_impl::<false>
    } else {
        scalar::argmin_u32_overlapping_hashed::<false>
    }
});

static ARGMIN_HASH_IMPL: LazyLock<ArgMinFn> = LazyLock::new(|| {
    if is_x86_feature_detected!("avx512f") {
        avx512_impl::<true>
    } else if is_x86_feature_detected!("avx2") {
        avx2_impl::<true>
    } else if is_x86_feature_detected!("sse4.1") {
        sse41_impl::<true>
    } else {
        scalar::argmin_u32_overlapping_hashed::<true>
    }
});

pub fn argmin_u32_overlapping_hashed<const SHOULD_HASH: bool>(
    bytes: &[u8],
    multiplier: u32,
    addend: u32,
) -> usize {
    const MIN_SIMD_LEN: usize = 16 + 3;
    assert!(bytes.len() <= u32::MAX as usize);

    let within_four_offset = if SHOULD_HASH {
        unsafe { ARGMIN_HASH_IMPL(bytes, multiplier, addend) }
    } else {
        unsafe { ARGMIN_IMPL(bytes, multiplier, addend) }
    };

    if bytes.len() >= MIN_SIMD_LEN {
        let final_bump = scalar::argmin_u32_overlapping_hashed_four::<SHOULD_HASH>(
            &bytes[within_four_offset..],
            multiplier,
            addend,
        );
        within_four_offset + final_bump
    } else {
        within_four_offset
    }
}