/* crc32_braid.c -- compute the CRC-32 of a data stream * Copyright (C) 1995-2022 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h * * This interleaved implementation of a CRC makes use of pipelined multiple * arithmetic-logic units, commonly found in modern CPU cores. It is due to * Kadatch and Jenkins (2010). See doc/crc-doc.1.0.pdf in this distribution. */ #include "zbuild.h" #include "crc32_braid_p.h" #include "crc32_braid_tbl.h" #include "crc32_p.h" /* A CRC of a message is computed on BRAID_N braids of words in the message, where each word consists of BRAID_W bytes (4 or 8). If BRAID_N is 3, for example, then three running sparse CRCs are calculated respectively on each braid, at these indices in the array of words: 0, 3, 6, ..., 1, 4, 7, ..., and 2, 5, 8, ... This is done starting at a word boundary, and continues until as many blocks of BRAID_N * BRAID_W bytes as are available have been processed. The results are combined into a single CRC at the end. For this code, BRAID_N must be in the range 1..6 and BRAID_W must be 4 or 8. The upper limit on BRAID_N can be increased if desired by adding more #if blocks, extending the patterns apparent in the code. In addition, crc32 tables would need to be regenerated, if the maximum BRAID_N value is increased. BRAID_N and BRAID_W are chosen empirically by benchmarking the execution time on a given processor. The choices for BRAID_N and BRAID_W below were based on testing on Intel Kaby Lake i7, AMD Ryzen 7, ARM Cortex-A57, Sparc64-VII, PowerPC POWER9, and MIPS64 Octeon II processors. The Intel, AMD, and ARM processors were all fastest with BRAID_N=5, BRAID_W=8. The Sparc, PowerPC, and MIPS64 were all fastest at BRAID_N=5, BRAID_W=4. They were all tested with either gcc or clang, all using the -O3 optimization level. Your mileage may vary. */ /* ========================================================================= */ #ifdef BRAID_W /* Return the CRC of the BRAID_W bytes in the word_t data, taking the least-significant byte of the word as the first byte of data, without any pre or post conditioning. This is used to combine the CRCs of each braid. */ # if BYTE_ORDER == LITTLE_ENDIAN static uint32_t crc_word(z_word_t data) { int k; for (k = 0; k < BRAID_W; k++) data = (data >> 8) ^ crc_table[data & 0xff]; return (uint32_t)data; } # elif BYTE_ORDER == BIG_ENDIAN static z_word_t crc_word(z_word_t data) { int k; for (k = 0; k < BRAID_W; k++) data = (data << 8) ^ crc_big_table[(data >> ((BRAID_W - 1) << 3)) & 0xff]; return data; } # endif /* BYTE_ORDER */ #endif /* BRAID_W */ /* ========================================================================= */ Z_INTERNAL uint32_t crc32_braid(uint32_t crc, const uint8_t *buf, size_t len) { crc = ~crc; #ifdef BRAID_W /* If provided enough bytes, do a braided CRC calculation. */ if (len >= BRAID_N * BRAID_W + BRAID_W - 1) { size_t blks; z_word_t const *words; int k; /* Compute the CRC up to a z_word_t boundary. */ size_t align_diff = (size_t)MIN(ALIGN_DIFF(buf, BRAID_W), len); if (align_diff) { crc = crc32_copy_small(crc, NULL, buf, align_diff, BRAID_W - 1, 0); len -= align_diff; buf += align_diff; } /* Compute the CRC on as many BRAID_N z_word_t blocks as are available. */ blks = len / (BRAID_N * BRAID_W); len -= blks * BRAID_N * BRAID_W; words = (z_word_t const *)buf; z_word_t crc0, word0, comb; #if BRAID_N > 1 z_word_t crc1, word1; #if BRAID_N > 2 z_word_t crc2, word2; #if BRAID_N > 3 z_word_t crc3, word3; #if BRAID_N > 4 z_word_t crc4, word4; #if BRAID_N > 5 z_word_t crc5, word5; #endif #endif #endif #endif #endif /* Initialize the CRC for each braid. */ crc0 = Z_WORD_FROM_LE(crc); #if BRAID_N > 1 crc1 = 0; #if BRAID_N > 2 crc2 = 0; #if BRAID_N > 3 crc3 = 0; #if BRAID_N > 4 crc4 = 0; #if BRAID_N > 5 crc5 = 0; #endif #endif #endif #endif #endif /* Process the first blks-1 blocks, computing the CRCs on each braid independently. */ while (--blks) { /* Load the word for each braid into registers. */ word0 = crc0 ^ words[0]; #if BRAID_N > 1 word1 = crc1 ^ words[1]; #if BRAID_N > 2 word2 = crc2 ^ words[2]; #if BRAID_N > 3 word3 = crc3 ^ words[3]; #if BRAID_N > 4 word4 = crc4 ^ words[4]; #if BRAID_N > 5 word5 = crc5 ^ words[5]; #endif #endif #endif #endif #endif words += BRAID_N; /* Compute and update the CRC for each word. The loop should get unrolled. */ crc0 = BRAID_TABLE[0][word0 & 0xff]; #if BRAID_N > 1 crc1 = BRAID_TABLE[0][word1 & 0xff]; #if BRAID_N > 2 crc2 = BRAID_TABLE[0][word2 & 0xff]; #if BRAID_N > 3 crc3 = BRAID_TABLE[0][word3 & 0xff]; #if BRAID_N > 4 crc4 = BRAID_TABLE[0][word4 & 0xff]; #if BRAID_N > 5 crc5 = BRAID_TABLE[0][word5 & 0xff]; #endif #endif #endif #endif #endif for (k = 1; k < BRAID_W; k++) { crc0 ^= BRAID_TABLE[k][(word0 >> (k << 3)) & 0xff]; #if BRAID_N > 1 crc1 ^= BRAID_TABLE[k][(word1 >> (k << 3)) & 0xff]; #if BRAID_N > 2 crc2 ^= BRAID_TABLE[k][(word2 >> (k << 3)) & 0xff]; #if BRAID_N > 3 crc3 ^= BRAID_TABLE[k][(word3 >> (k << 3)) & 0xff]; #if BRAID_N > 4 crc4 ^= BRAID_TABLE[k][(word4 >> (k << 3)) & 0xff]; #if BRAID_N > 5 crc5 ^= BRAID_TABLE[k][(word5 >> (k << 3)) & 0xff]; #endif #endif #endif #endif #endif } } /* Process the last block, combining the CRCs of the BRAID_N braids at the same time. */ comb = crc_word(crc0 ^ words[0]); #if BRAID_N > 1 comb = crc_word(crc1 ^ words[1] ^ comb); #if BRAID_N > 2 comb = crc_word(crc2 ^ words[2] ^ comb); #if BRAID_N > 3 comb = crc_word(crc3 ^ words[3] ^ comb); #if BRAID_N > 4 comb = crc_word(crc4 ^ words[4] ^ comb); #if BRAID_N > 5 comb = crc_word(crc5 ^ words[5] ^ comb); #endif #endif #endif #endif #endif words += BRAID_N; Assert(comb <= UINT32_MAX, "comb should fit in uint32_t"); crc = (uint32_t)Z_WORD_FROM_LE(comb); /* Update the pointer to the remaining bytes to process. */ buf = (const unsigned char *)words; } #endif /* BRAID_W */ /* Complete the computation of the CRC on any remaining bytes. */ return ~crc32_copy_small(crc, NULL, buf, len, (BRAID_N * BRAID_W) - 1, 0); } Z_INTERNAL uint32_t crc32_copy_braid(uint32_t crc, uint8_t *dst, const uint8_t *src, size_t len) { crc = crc32_braid(crc, src, len); memcpy(dst, src, len); return crc; }