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Commit235328e

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Revert "Speed up tail processing when hashing aligned C strings, take two"
This reverts commita365d9e.Older versions of Valgrind raise an error, so go back to the bytewiseloop for the final word in the input.Reported-by: Anton A. Melnikov <a.melnikov@postgrespro.ru>Discussion:https://postgr.es/m/a3a959f6-14b8-4819-ac04-eaf2aa2e868d@postgrespro.ruBackpatch-through: 17
1 parent4f07134 commit235328e

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1 file changed

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‎src/include/common/hashfn_unstable.h

Lines changed: 10 additions & 36 deletions
Original file line numberDiff line numberDiff line change
@@ -219,13 +219,6 @@ fasthash_accum(fasthash_state *hs, const char *k, size_t len)
219219
#definehaszero64(v) \
220220
(((v) - 0x0101010101010101) & ~(v) & 0x8080808080808080)
221221

222-
/* get first byte in memory order */
223-
#ifdefWORDS_BIGENDIAN
224-
#definefirstbyte64(v) ((v) >> 56)
225-
#else
226-
#definefirstbyte64(v) ((v) & 0xFF)
227-
#endif
228-
229222
/*
230223
* all-purpose workhorse for fasthash_accum_cstring
231224
*/
@@ -262,7 +255,7 @@ static inline size_t
262255
fasthash_accum_cstring_aligned(fasthash_state*hs,constchar*str)
263256
{
264257
constchar*conststart=str;
265-
uint64chunk;
258+
size_tremainder;
266259
uint64zero_byte_low;
267260

268261
Assert(PointerIsAligned(start,uint64));
@@ -282,7 +275,7 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
282275
*/
283276
for (;;)
284277
{
285-
chunk=*(uint64*)str;
278+
uint64chunk=*(uint64*)str;
286279

287280
#ifdefWORDS_BIGENDIAN
288281
zero_byte_low=haszero64(pg_bswap64(chunk));
@@ -297,33 +290,14 @@ fasthash_accum_cstring_aligned(fasthash_state *hs, const char *str)
297290
str+=FH_SIZEOF_ACCUM;
298291
}
299292

300-
if (firstbyte64(chunk)!=0)
301-
{
302-
size_tremainder;
303-
uint64mask;
304-
305-
/*
306-
* The byte corresponding to the NUL will be 0x80, so the rightmost
307-
* bit position will be in the range 15, 23, ..., 63. Turn this into
308-
* byte position by dividing by 8.
309-
*/
310-
remainder=pg_rightmost_one_pos64(zero_byte_low) /BITS_PER_BYTE;
311-
312-
/*
313-
* Create a mask for the remaining bytes so we can combine them into
314-
* the hash. This must have the same result as mixing the remaining
315-
* bytes with fasthash_accum().
316-
*/
317-
#ifdefWORDS_BIGENDIAN
318-
mask= ~UINT64CONST(0) <<BITS_PER_BYTE* (FH_SIZEOF_ACCUM-remainder);
319-
#else
320-
mask= ~UINT64CONST(0) >>BITS_PER_BYTE* (FH_SIZEOF_ACCUM-remainder);
321-
#endif
322-
hs->accum=chunk&mask;
323-
fasthash_combine(hs);
324-
325-
str+=remainder;
326-
}
293+
/*
294+
* The byte corresponding to the NUL will be 0x80, so the rightmost bit
295+
* position will be in the range 7, 15, ..., 63. Turn this into byte
296+
* position by dividing by 8.
297+
*/
298+
remainder=pg_rightmost_one_pos64(zero_byte_low) /BITS_PER_BYTE;
299+
fasthash_accum(hs,str,remainder);
300+
str+=remainder;
327301

328302
returnstr-start;
329303
}

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