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liblzma: Remove CRC_USE_GENERIC_FOR_SMALL_INPUTS 

It was already commented out.
This commit is contained in:
Lasse Collin 2024-05-09 21:44:03 +03:00
parent f99a7be406
commit 71b147aab7
4 changed files with 1 additions and 48 deletions
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21
src/liblzma/check/crc32_fast.c
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@ -164,27 +164,6 @@ extern LZMA_API(uint32_t)
lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
{
#if defined(CRC32_GENERIC) && defined(CRC32_ARCH_OPTIMIZED)
// On x86-64, if CLMUL is available, it is the best for non-tiny
// inputs, being over twice as fast as the generic slice-by-four
// version. However, for size <= 16 it's different. In the extreme
// case of size == 1 the generic version can be five times faster.
// At size >= 8 the CLMUL starts to become reasonable. It
// varies depending on the alignment of buf too.
//
// The above doesn't include the overhead of mythread_once().
// At least on x86-64 GNU/Linux, pthread_once() is very fast but
// it still makes lzma_crc32(buf, 1, crc) 50-100 % slower. When
// size reaches 12-16 bytes the overhead becomes negligible.
//
// So using the generic version for size <= 16 may give better
// performance with tiny inputs but if such inputs happen rarely
// it's not so obvious because then the lookup table of the
// generic version may not be in the processor cache.
#ifdef CRC_USE_GENERIC_FOR_SMALL_INPUTS
if (size <= 16)
return crc32_generic(buf, size, crc);
#endif
/*
#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
// See crc32_dispatch(). This would be the alternative which uses

5
src/liblzma/check/crc64_fast.c
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@ -134,11 +134,6 @@ extern LZMA_API(uint64_t)
lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
{
#if defined(CRC64_GENERIC) && defined(CRC64_ARCH_OPTIMIZED)
#ifdef CRC_USE_GENERIC_FOR_SMALL_INPUTS
if (size <= 16)
return crc64_generic(buf, size, crc);
#endif
return crc64_func(buf, size, crc);
#elif defined(CRC64_ARCH_OPTIMIZED)

14
src/liblzma/check/crc_common.h
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@ -59,8 +59,6 @@
#undef CRC32_ARM64
#undef CRC64_ARM64_CLMUL
#undef CRC_USE_GENERIC_FOR_SMALL_INPUTS
// ARM64 CRC32 instruction is only useful for CRC32. Currently, only
// little endian is supported since we were unable to test on a big
// endian machine.
@ -99,18 +97,6 @@
# define CRC32_ARCH_OPTIMIZED 1
# define CRC64_ARCH_OPTIMIZED 1
# define CRC_X86_CLMUL 1
/*
// The generic code is much faster with 1-8-byte inputs and
// has similar performance up to 16 bytes at least in
// microbenchmarks (it depends on input buffer alignment
// too). If both versions are built, this #define will use
// the generic version for inputs up to 16 bytes and CLMUL
// for bigger inputs. It saves a little in code size since
// the special cases for 0-16-byte inputs will be omitted
// from the CLMUL code.
# define CRC_USE_GENERIC_FOR_SMALL_INPUTS 1
*/
# endif
#endif

9
src/liblzma/check/crc_x86_clmul.h
View File

@ -130,7 +130,6 @@ crc_simd_body(const uint8_t *buf, const size_t size, __m128i *v0, __m128i *v1,
__m128i v2, v3;
#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
if (size <= 16) {
// Right-shift initial_crc by 1-16 bytes based on "size"
// and store the result in v1 (high bytes) and v0 (low bytes).
@ -173,9 +172,7 @@ crc_simd_body(const uint8_t *buf, const size_t size, __m128i *v0, __m128i *v1,
*v0 = _mm_xor_si128(*v0, v3);
*v1 = _mm_alignr_epi8(*v1, *v0, 8);
} else
#endif
{
} else {
// There is more than 16 bytes of input.
const __m128i data1 = _mm_load_si128(aligned_buf);
const __m128i *end = (const __m128i*)(
@ -245,11 +242,9 @@ crc_attr_target
static uint32_t
crc32_arch_optimized(const uint8_t *buf, size_t size, uint32_t crc)
{
#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
// The code assumes that there is at least one byte of input.
if (size == 0)
return crc;
#endif
// uint32_t poly = 0xedb88320;
const int64_t p = 0x1db710640; // p << 1
@ -334,11 +329,9 @@ crc_attr_target
static uint64_t
crc64_arch_optimized(const uint8_t *buf, size_t size, uint64_t crc)
{
#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
// The code assumes that there is at least one byte of input.
if (size == 0)
return crc;
#endif
// const uint64_t poly = 0xc96c5795d7870f42; // CRC polynomial
const uint64_t p = 0x92d8af2baf0e1e85; // (poly << 1) | 1