vortex-fastlanes 0.70.0

Vortex fastlanes arrays
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

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright the Vortex contributors

use crate::bit_transpose::BASE_PATTERN_FIRST;
use crate::bit_transpose::BASE_PATTERN_SECOND;
use crate::bit_transpose::TRANSPOSE_2X2;
use crate::bit_transpose::TRANSPOSE_4X4;
use crate::bit_transpose::TRANSPOSE_8X8;

/// Fast scalar transpose using the 8x8 bit matrix transpose algorithm.
///
/// This version uses 64-bit gather + parallel bit operations instead of
/// extracting bits one by one. Typically 5-10x faster than the basic scalar version.
#[inline(never)]
#[allow(dead_code)]
pub fn transpose_bits_scalar(input: &[u8; 128], output: &mut [u8; 128]) {
    // Helper to perform 8x8 bit transpose on a u64 (each byte becomes a row)
    fn transpose_8x8(mut x: u64) -> u64 {
        // Step 1: Transpose 2x2 bit blocks
        let t = (x ^ (x >> 7)) & TRANSPOSE_2X2;
        x = x ^ t ^ (t << 7);
        // Step 2: Transpose 4x4 bit blocks
        let t = (x ^ (x >> 14)) & TRANSPOSE_4X4;
        x = x ^ t ^ (t << 14);
        // Step 3: Transpose 8x8 bit blocks
        let t = (x ^ (x >> 28)) & TRANSPOSE_8X8;
        x ^ t ^ (t << 28)
    }

    // Helper to gather 8 bytes at stride 16 into a u64
    fn gather(input: &[u8; 128], base: usize) -> u64 {
        u64::from(input[base])
            | (u64::from(input[base + 16]) << 8)
            | (u64::from(input[base + 32]) << 16)
            | (u64::from(input[base + 48]) << 24)
            | (u64::from(input[base + 64]) << 32)
            | (u64::from(input[base + 80]) << 40)
            | (u64::from(input[base + 96]) << 48)
            | (u64::from(input[base + 112]) << 56)
    }

    // Process first half (8 base groups, fully unrolled)
    let r0 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[0]));
    let r1 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[1]));
    let r2 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[2]));
    let r3 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[3]));
    let r4 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[4]));
    let r5 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[5]));
    let r6 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[6]));
    let r7 = transpose_8x8(gather(input, BASE_PATTERN_FIRST[7]));

    // Write first 64 output bytes (unrolled)
    for bit_pos in 0..8 {
        output[bit_pos * 8] = (r0 >> (bit_pos * 8)) as u8;
        output[bit_pos * 8 + 1] = (r1 >> (bit_pos * 8)) as u8;
        output[bit_pos * 8 + 2] = (r2 >> (bit_pos * 8)) as u8;
        output[bit_pos * 8 + 3] = (r3 >> (bit_pos * 8)) as u8;
        output[bit_pos * 8 + 4] = (r4 >> (bit_pos * 8)) as u8;
        output[bit_pos * 8 + 5] = (r5 >> (bit_pos * 8)) as u8;
        output[bit_pos * 8 + 6] = (r6 >> (bit_pos * 8)) as u8;
        output[bit_pos * 8 + 7] = (r7 >> (bit_pos * 8)) as u8;
    }

    // Process second half
    let r0 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[0]));
    let r1 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[1]));
    let r2 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[2]));
    let r3 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[3]));
    let r4 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[4]));
    let r5 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[5]));
    let r6 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[6]));
    let r7 = transpose_8x8(gather(input, BASE_PATTERN_SECOND[7]));

    for bit_pos in 0..8 {
        output[64 + bit_pos * 8] = (r0 >> (bit_pos * 8)) as u8;
        output[64 + bit_pos * 8 + 1] = (r1 >> (bit_pos * 8)) as u8;
        output[64 + bit_pos * 8 + 2] = (r2 >> (bit_pos * 8)) as u8;
        output[64 + bit_pos * 8 + 3] = (r3 >> (bit_pos * 8)) as u8;
        output[64 + bit_pos * 8 + 4] = (r4 >> (bit_pos * 8)) as u8;
        output[64 + bit_pos * 8 + 5] = (r5 >> (bit_pos * 8)) as u8;
        output[64 + bit_pos * 8 + 6] = (r6 >> (bit_pos * 8)) as u8;
        output[64 + bit_pos * 8 + 7] = (r7 >> (bit_pos * 8)) as u8;
    }
}

/// Fast scalar untranspose using the 8x8 bit matrix transpose algorithm.
#[inline(never)]
#[allow(dead_code)]
pub fn untranspose_bits_scalar(input: &[u8; 128], output: &mut [u8; 128]) {
    fn transpose_8x8(mut x: u64) -> u64 {
        let t = (x ^ (x >> 7)) & TRANSPOSE_2X2;
        x = x ^ t ^ (t << 7);
        let t = (x ^ (x >> 14)) & TRANSPOSE_4X4;
        x = x ^ t ^ (t << 14);
        let t = (x ^ (x >> 28)) & TRANSPOSE_8X8;
        x ^ t ^ (t << 28)
    }

    fn gather_transposed(input: &[u8; 128], base_group: usize, offset: usize) -> u64 {
        let mut result: u64 = 0;
        for bit_pos in 0..8 {
            result |= u64::from(input[offset + bit_pos * 8 + base_group]) << (bit_pos * 8);
        }
        result
    }

    fn scatter(output: &mut [u8; 128], base: usize, val: u64) {
        output[base] = val as u8;
        output[base + 16] = (val >> 8) as u8;
        output[base + 32] = (val >> 16) as u8;
        output[base + 48] = (val >> 24) as u8;
        output[base + 64] = (val >> 32) as u8;
        output[base + 80] = (val >> 40) as u8;
        output[base + 96] = (val >> 48) as u8;
        output[base + 112] = (val >> 56) as u8;
    }

    // First half (unrolled)
    let r0 = transpose_8x8(gather_transposed(input, 0, 0));
    let r1 = transpose_8x8(gather_transposed(input, 1, 0));
    let r2 = transpose_8x8(gather_transposed(input, 2, 0));
    let r3 = transpose_8x8(gather_transposed(input, 3, 0));
    let r4 = transpose_8x8(gather_transposed(input, 4, 0));
    let r5 = transpose_8x8(gather_transposed(input, 5, 0));
    let r6 = transpose_8x8(gather_transposed(input, 6, 0));
    let r7 = transpose_8x8(gather_transposed(input, 7, 0));

    scatter(output, BASE_PATTERN_FIRST[0], r0);
    scatter(output, BASE_PATTERN_FIRST[1], r1);
    scatter(output, BASE_PATTERN_FIRST[2], r2);
    scatter(output, BASE_PATTERN_FIRST[3], r3);
    scatter(output, BASE_PATTERN_FIRST[4], r4);
    scatter(output, BASE_PATTERN_FIRST[5], r5);
    scatter(output, BASE_PATTERN_FIRST[6], r6);
    scatter(output, BASE_PATTERN_FIRST[7], r7);

    // Second half
    let r0 = transpose_8x8(gather_transposed(input, 0, 64));
    let r1 = transpose_8x8(gather_transposed(input, 1, 64));
    let r2 = transpose_8x8(gather_transposed(input, 2, 64));
    let r3 = transpose_8x8(gather_transposed(input, 3, 64));
    let r4 = transpose_8x8(gather_transposed(input, 4, 64));
    let r5 = transpose_8x8(gather_transposed(input, 5, 64));
    let r6 = transpose_8x8(gather_transposed(input, 6, 64));
    let r7 = transpose_8x8(gather_transposed(input, 7, 64));

    scatter(output, BASE_PATTERN_SECOND[0], r0);
    scatter(output, BASE_PATTERN_SECOND[1], r1);
    scatter(output, BASE_PATTERN_SECOND[2], r2);
    scatter(output, BASE_PATTERN_SECOND[3], r3);
    scatter(output, BASE_PATTERN_SECOND[4], r4);
    scatter(output, BASE_PATTERN_SECOND[5], r5);
    scatter(output, BASE_PATTERN_SECOND[6], r6);
    scatter(output, BASE_PATTERN_SECOND[7], r7);
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::bit_transpose::generate_test_data;

    #[test]
    fn test_scalar_matches_baseline() {
        for seed in [0, 42, 123, 255] {
            let input = generate_test_data(seed);
            let mut baseline_out = [0u8; 128];
            let mut fast_out = [0u8; 128];

            transpose_bits_scalar(&input, &mut baseline_out);
            transpose_bits_scalar(&input, &mut fast_out);

            assert_eq!(
                baseline_out, fast_out,
                "scalar_fast transpose doesn't match baseline for seed {seed}"
            );
        }
    }

    #[test]
    fn test_scalar_roundtrip() {
        for seed in [0, 42, 123, 255] {
            let input = generate_test_data(seed);
            let mut transposed = [0u8; 128];
            let mut roundtrip = [0u8; 128];

            transpose_bits_scalar(&input, &mut transposed);
            untranspose_bits_scalar(&transposed, &mut roundtrip);

            assert_eq!(
                input, roundtrip,
                "scalar_fast roundtrip failed for seed {seed}"
            );
        }
    }

    #[test]
    fn test_all_zeros() {
        let input = [0u8; 128];
        let mut output = [0xFFu8; 128];

        transpose_bits_scalar(&input, &mut output);
        assert_eq!(output, [0u8; 128]);

        untranspose_bits_scalar(&input, &mut output);
        assert_eq!(output, [0u8; 128]);
    }

    #[test]
    fn test_all_ones() {
        let input = [0xFFu8; 128];
        let mut output = [0u8; 128];

        transpose_bits_scalar(&input, &mut output);
        assert_eq!(output, [0xFFu8; 128]);

        untranspose_bits_scalar(&input, &mut output);
        assert_eq!(output, [0xFFu8; 128]);
    }
}