circuitpython/shared-module/bitops/__init__.c

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/*
* This file is part of the CircuitPython project, https://github.com/adafruit/circuitpython
*
* The MIT License (MIT)
*
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* Copyright (c) 2021 Jeff Epler for Adafruit Industries
*
* 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 "shared-bindings/bitops/__init__.h"
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include "py/mpconfig.h"
// adapted from "Hacker's Delight" - Figure 7-2 Transposing an 8x8-bit matrix
// basic idea is:
// > First, treat the 8x8-bit matrix as 16 2x2-bit matrices, and transpose each
// > of the 16 2x2-bit matrices. Second, treat the matrix as four 2x2 submatrices
// > whose elements are 2x2-bit matrices and transpose each of the four 2x2
// > submatrices. Finally, treat the matrix as a 2x2 matrix whose elements are
// > 4x4-bit matrices, and transpose the 2x2 matrix. These transformations are
// > illustrated below.
// We want a different definition of bit/byte order, deal with strides differently, etc.
// so the code is heavily re-worked compared to the original.
static void transpose_var(uint32_t *result, const uint8_t *src, int src_stride, int num_strands) {
uint32_t x = 0, y = 0, t;
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src += (num_strands - 1) * src_stride;
switch (num_strands) {
case 7:
x |= *src << 16;
src -= src_stride;
MP_FALLTHROUGH;
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case 6:
x |= *src << 8;
src -= src_stride;
MP_FALLTHROUGH;
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case 5:
x |= *src;
src -= src_stride;
MP_FALLTHROUGH;
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case 4:
y |= *src << 24;
src -= src_stride;
MP_FALLTHROUGH;
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case 3:
y |= *src << 16;
src -= src_stride;
MP_FALLTHROUGH;
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case 2:
y |= *src << 8;
src -= src_stride;
y |= *src;
}
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t = (x ^ (x >> 7)) & 0x00AA00AA;
x = x ^ t ^ (t << 7);
t = (y ^ (y >> 7)) & 0x00AA00AA;
y = y ^ t ^ (t << 7);
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t = (x ^ (x >> 14)) & 0x0000CCCC;
x = x ^ t ^ (t << 14);
t = (y ^ (y >> 14)) & 0x0000CCCC;
y = y ^ t ^ (t << 14);
t = (x & 0xF0F0F0F0) | ((y >> 4) & 0x0F0F0F0F);
y = ((x << 4) & 0xF0F0F0F0) | (y & 0x0F0F0F0F);
x = t;
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#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
x = __builtin_bswap32(x);
y = __builtin_bswap32(y);
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#endif
result[0] = x;
result[1] = y;
}
static void transpose_8(uint32_t *result, const uint8_t *src, int src_stride) {
uint32_t x, y, t;
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y = *src;
src += src_stride;
y |= (*src << 8);
src += src_stride;
y |= (*src << 16);
src += src_stride;
y |= (*src << 24);
src += src_stride;
x = *src;
src += src_stride;
x |= (*src << 8);
src += src_stride;
x |= (*src << 16);
src += src_stride;
x |= (*src << 24);
src += src_stride;
t = (x ^ (x >> 7)) & 0x00AA00AA;
x = x ^ t ^ (t << 7);
t = (y ^ (y >> 7)) & 0x00AA00AA;
y = y ^ t ^ (t << 7);
t = (x ^ (x >> 14)) & 0x0000CCCC;
x = x ^ t ^ (t << 14);
t = (y ^ (y >> 14)) & 0x0000CCCC;
y = y ^ t ^ (t << 14);
t = (x & 0xF0F0F0F0) | ((y >> 4) & 0x0F0F0F0F);
y = ((x << 4) & 0xF0F0F0F0) | (y & 0x0F0F0F0F);
x = t;
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#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
x = __builtin_bswap32(x);
y = __builtin_bswap32(y);
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#endif
result[0] = x;
result[1] = y;
}
static void bit_transpose_8(uint32_t *result, const uint8_t *src, size_t src_stride, size_t n) {
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for (size_t i = 0; i < n; i++) {
transpose_8(result, src, src_stride);
result += 2;
src += 1;
}
}
static void bit_transpose_var(uint32_t *result, const uint8_t *src, size_t src_stride, size_t n, int num_strands) {
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for (size_t i = 0; i < n; i++) {
transpose_var(result, src, src_stride, num_strands);
result += 2;
src += 1;
}
}
void common_hal_bitops_bit_transpose(uint8_t *result, const uint8_t *src, size_t inlen, size_t num_strands) {
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if (num_strands == 8) {
bit_transpose_8((uint32_t *)(void *)result, src, inlen / 8, inlen / 8);
} else {
bit_transpose_var((uint32_t *)(void *)result, src, inlen / num_strands, inlen / num_strands, num_strands);
}
}