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Revert "Speed up tail processing when hashing aligned C strings" 

This reverts commit 07f0f6abfc.

This has shown failures on both Valgrind and big-endian machines,
per members skink and pike.
This commit is contained in:
John Naylor 2024-03-31 14:18:36 +07:00
parent 07f0f6abfc
commit f4ad0021af
1 changed files with 10 additions and 34 deletions
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44
src/include/common/hashfn_unstable.h
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@ -219,9 +219,8 @@ static inline size_t
fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
{
const char *const start = str;
uint64 chunk;
size_t remainder;
uint64 zero_byte_low;
uint64 mask;
Assert(PointerIsAligned(start, uint64));
@ -240,7 +239,7 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
*/
for (;;)
{
chunk = *(uint64 *) str;
uint64 chunk = *(uint64 *) str;
#ifdef WORDS_BIGENDIAN
zero_byte_low = haszero64(pg_bswap64(chunk));
@ -255,37 +254,14 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
str += FH_SIZEOF_ACCUM;
}
if (zero_byte_low & 0xFF)
{
/*
* The next byte in the input is the NUL terminator, so we have
* nothing to do.
*/
}
else
{
/*
* Create a mask for the remaining bytes so we can combine them into
* the hash. The mask also covers the NUL terminator, but that's
* harmless. The mask could contain 0x80 in bytes corresponding to the
* input past the terminator, but only where the input byte is zero or
* one, so also harmless.
*/
mask = zero_byte_low | (zero_byte_low - 1);
#ifdef WORDS_BIGENDIAN
/* need to mask the upper bytes */
mask = pg_bswap64(mask);
#endif
hs->accum = chunk & mask;
fasthash_combine(hs);
/*
* The byte corresponding to the NUL will be 0x80, so the rightmost
* bit position will be in the range 15, 23, ..., 63. Turn this into
* byte position by dividing by 8.
*/
str += pg_rightmost_one_pos64(zero_byte_low) / BITS_PER_BYTE;
}
/*
* The byte corresponding to the NUL will be 0x80, so the rightmost bit
* position will be in the range 7, 15, ..., 63. Turn this into byte
* position by dividing by 8.
*/
remainder = pg_rightmost_one_pos64(zero_byte_low) / BITS_PER_BYTE;
fasthash_accum(hs, str, remainder);
str += remainder;
return str - start;
}