diff options
| -rw-r--r-- | crc32.c | 114 |
1 files changed, 114 insertions, 0 deletions
@@ -617,6 +617,118 @@ const z_crc_t FAR * ZEXPORT get_crc_table() return (const z_crc_t FAR *)crc_table; } +/* ========================================================================= + * Use ARM machine instructions if requested. This will compute the CRC about + * ten times faster than the braided calculation. This code does not check for + * the presence of the CRC instruction. Compile with care. + */ +#if defined(Z_ARM_CRC32) && defined(__aarch64__) && W == 8 + +/* + Constants empirically determined to maximize speed. These values are from + measurements on a Cortex-A57. Your mileage may vary. + */ +#define Z_BATCH 3990 /* number of words in a batch */ +#define Z_BATCH_ZEROS 0xa10d3d0c /* computed from Z_BATCH = 3990 */ +#define Z_BATCH_MIN 800 /* fewest words in a final batch */ + +unsigned long ZEXPORT crc32_z(crc, buf, len) + unsigned long crc; + const unsigned char FAR *buf; + z_size_t len; +{ + z_crc_t val; + z_word_t crc1, crc2; + const z_word_t *word; + z_word_t val0, val1, val2; + z_size_t last, last2, i; + z_size_t num; + + /* Return initial CRC, if requested. */ + if (buf == Z_NULL) return 0; + +#ifdef DYNAMIC_CRC_TABLE + once(&made, make_crc_table); +#endif /* DYNAMIC_CRC_TABLE */ + + /* Pre-condition the CRC */ + crc ^= 0xffffffff; + + /* Compute the CRC up to a word boundary. */ + while (len && ((z_size_t)buf & 7) != 0) { + len--; + val = *buf++; + __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val)); + } + + /* Prepare to compute the CRC on full 64-bit words word[0..num-1]. */ + word = (z_word_t const *)buf; + num = len >> 3; + len &= 7; + + /* Do three interleaved CRCs to realize the throughput of one crc32x + instruction per cycle. Each CRC is calcuated on Z_BATCH words. The three + CRCs are combined into a single CRC after each set of batches. */ + while (num >= 3 * Z_BATCH) { + crc1 = 0; + crc2 = 0; + for (i = 0; i < Z_BATCH; i++) { + val0 = word[i]; + val1 = word[i + Z_BATCH]; + val2 = word[i + 2 * Z_BATCH]; + __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0)); + __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1)); + __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2)); + } + word += 3 * Z_BATCH; + num -= 3 * Z_BATCH; + crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc1; + crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc2; + } + + /* Do one last smaller batch with the remaining words, if there are enough + to pay for the combination of CRCs. */ + last = num / 3; + if (last >= Z_BATCH_MIN) { + last2 = last << 1; + crc1 = 0; + crc2 = 0; + for (i = 0; i < last; i++) { + val0 = word[i]; + val1 = word[i + last]; + val2 = word[i + last2]; + __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0)); + __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1)); + __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2)); + } + word += 3 * last; + num -= 3 * last; + val = x2nmodp(last, 6); + crc = multmodp(val, crc) ^ crc1; + crc = multmodp(val, crc) ^ crc2; + } + + /* Compute the CRC on any remaining words. */ + for (i = 0; i < num; i++) { + val0 = word[i]; + __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0)); + } + word += num; + + /* Complete the CRC on any remaining bytes. */ + buf = (const unsigned char FAR *)word; + while (len) { + len--; + val = *buf++; + __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val)); + } + + /* Return the CRC, post-conditioned. */ + return crc ^ 0xffffffff; +} + +#else + /* ========================================================================= */ unsigned long ZEXPORT crc32_z(crc, buf, len) unsigned long crc; @@ -939,6 +1051,8 @@ unsigned long ZEXPORT crc32_z(crc, buf, len) return crc ^ 0xffffffff; } +#endif + /* ========================================================================= */ unsigned long ZEXPORT crc32(crc, buf, len) unsigned long crc; |