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ARCH/X86: Use UCS function to count leading zeros #10514

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ARCH/X86: Use UCS function to count leading zeros #10514

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ARCH/X86: Use UCS function to count leading zeros
tvegas1 Feb 24, 2025
58368cb
ARCH/X86: Use UCS function to count leading zeros
tvegas1 Feb 25, 2025
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6 changes: 1 addition & 5 deletions src/ucs/arch/x86_64/cpu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1063,10 +1063,9 @@ size_t ucs_x86_nt_src_buffer_transfer(void *dst, const void *src, size_t len)
static UCS_F_ALWAYS_INLINE
void ucs_x86_copy_bytes_le_128(void *dst, const void *src, size_t len)
{
#if defined (__LZCNT__)
__m256i y0, y1, y2, y3;
/* Handle lengths that fall usually within eager short range */
switch (_lzcnt_u32(len)) {
switch (ucs_count_leading_zero_bits(len)) {
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If the len is zero the code expects '32' as output, is ucs_count_leading_zero_bits(0) return 32?

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yes you're right, should be fixed now

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@arun-chandran-edarath arun-chandran-edarath Feb 26, 2025 •
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There is one issue; _lzcnt_u32(len) is expected to count the leading zeros from a 32bit operand.

_lzcnt_u32(0) should produce 32.

But now ucs_count_leading_zero_bits(len) will use _lzcnt_u64() because 'size_t len' will be 8 byte and the outputs produced makes the switch_cases wrong. [_lzcnt_u64(0) gives 64]

It should be ucs_count_leading_zero_bits((uint32_t) len) right?

/* 0 */
case 32:
break;
Expand Down Expand Up @@ -1121,9 +1120,6 @@ void ucs_x86_copy_bytes_le_128(void *dst, const void *src, size_t len)
_mm256_storeu_si256(UCS_PTR_BYTE_OFFSET(dst, len - 32), y3);
break;
}
#else
memcpy(dst, src, len);
#endif
}

/* This is an adaptation of the memcpy code from https://github.com/amd/aocl-libmem
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