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x86/crc32: optimize tail handling for crc32c short inputs

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For handling the 0 <= len < sizeof(unsigned long) bytes left at the end,
do a 4-2-1 step-down instead of a byte-at-a-time loop.  This allows
taking advantage of wider CRC instructions.  Note that crc32c-3way.S
already uses this same optimization too.

crc_kunit shows an improvement of about 25% for len=127.

Suggested-by: "H. Peter Anvin" <hpa@zytor.com>
Acked-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20250304213216.108925-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers 2025-03-04 13:32:16 -08:00
parent 511484fa88
commit 5aebe00b2f
1 changed files with 9 additions and 1 deletions
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10
arch/x86/lib/crc32-glue.c
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@ -57,7 +57,15 @@ u32 crc32c_arch(u32 crc, const u8 *p, size_t len)
num_longs != 0; num_longs--, p += sizeof(unsigned long))
asm(CRC32_INST : "+r" (crc) : ASM_INPUT_RM (*(unsigned long *)p));
for (len %= sizeof(unsigned long); len; len--, p++)
if (sizeof(unsigned long) > 4 && (len & 4)) {
asm("crc32l %1, %0" : "+r" (crc) : ASM_INPUT_RM (*(u32 *)p));
p += 4;
}
if (len & 2) {
asm("crc32w %1, %0" : "+r" (crc) : ASM_INPUT_RM (*(u16 *)p));
p += 2;
}
if (len & 1)
asm("crc32b %1, %0" : "+r" (crc) : ASM_INPUT_RM (*p));
return crc;