mirror of https://github.com/postgres/postgres
Modern x86 and x86-64 processors with SSE 4.2 support have special instructions, crc32b and crc32q, for calculating CRC-32C. They greatly speed up CRC calculation. Whether the instructions can be used or not depends on the compiler and the target architecture. If generation of SSE 4.2 instructions is allowed for the target (-msse4.2 flag on gcc and clang), use them. If they are not allowed by default, but the compiler supports the -msse4.2 flag to enable them, compile just the CRC-32C function with -msse4.2 flag, and check at runtime whether the processor we're running on supports it. If it doesn't, fall back to the slicing-by-8 algorithm. (With the common defaults on current operating systems, the runtime-check variant is what you get in practice.) Abhijit Menon-Sen, heavily modified by me, reviewed by Andres Freund.pull/14/head
Heikki Linnakangas
10 years ago
parent
4f700bcd20
commit
3dc2d62d04
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/*-------------------------------------------------------------------------
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* |
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* pg_crc32c_choose.c |
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* Choose which CRC-32C implementation to use, at runtime. |
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* |
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* Try to the special CRC instructions introduced in Intel SSE 4.2, |
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* if available on the platform we're running on, but fall back to the |
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* slicing-by-8 implementation otherwise. |
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* |
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* Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group |
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* Portions Copyright (c) 1994, Regents of the University of California |
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* |
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* |
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* IDENTIFICATION |
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* src/port/pg_crc32c_choose.c |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#include "c.h" |
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#ifdef HAVE__GET_CPUID |
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#include <cpuid.h> |
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#endif |
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#ifdef HAVE__CPUID |
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#include <intrin.h> |
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#endif |
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#include "port/pg_crc32c.h" |
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static bool |
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pg_crc32c_sse42_available(void) |
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{ |
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unsigned int exx[4] = {0, 0, 0, 0}; |
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#if defined(HAVE__GET_CPUID) |
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__get_cpuid(1, &exx[0], &exx[1], &exx[2], &exx[3]); |
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#elif defined(HAVE__CPUID) |
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__cpuid(exx, 1); |
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#else |
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#error cpuid instruction not available |
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#endif |
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return (exx[2] & (1 << 20)) != 0; /* SSE 4.2 */ |
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} |
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/*
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* This gets called on the first call. It replaces the function pointer |
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* so that subsequent calls are routed directly to the chosen implementation. |
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*/ |
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static pg_crc32c |
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pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len) |
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{ |
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if (pg_crc32c_sse42_available()) |
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pg_comp_crc32c = pg_comp_crc32c_sse42; |
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else |
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pg_comp_crc32c = pg_comp_crc32c_sb8; |
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return pg_comp_crc32c(crc, data, len); |
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} |
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pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose; |
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@ -0,0 +1,52 @@ |
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/*-------------------------------------------------------------------------
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* |
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* pg_crc32c_sse42.c |
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* Compute CRC-32C checksum using Intel SSE 4.2 instructions. |
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* |
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* Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group |
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* Portions Copyright (c) 1994, Regents of the University of California |
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* |
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* |
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* IDENTIFICATION |
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* src/port/pg_crc32c_sse42.c |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#include "c.h" |
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#include "port/pg_crc32c.h" |
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#include <nmmintrin.h> |
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pg_crc32c |
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pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len) |
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{ |
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const unsigned char *p = data; |
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const uint64 *p8; |
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/*
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* Process eight bytes of data at a time. |
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* |
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* NB: We do unaligned 8-byte accesses here. The Intel architecture |
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* allows that, and performance testing didn't show any performance |
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* gain from aligning the beginning address. |
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*/ |
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p8 = (const uint64 *) p; |
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while (len >= 8) |
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{ |
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crc = (uint32) _mm_crc32_u64(crc, *p8++); |
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len -= 8; |
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} |
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/*
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* Handle any remaining bytes one at a time. |
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*/ |
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p = (const unsigned char *) p8; |
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while (len > 0) |
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{ |
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crc = _mm_crc32_u8(crc, *p++); |
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len--; |
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} |
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return crc; |
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} |
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