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Commit0c25fee

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Teach fasthash_accum to use platform endianness for bytewise loads
This function previously used a mix of word-wise loads and bytewiseloads. The bytewise loads happened to be little-endian regardless ofplatform. This in itself is not a problem. However, a future commitwill require the same result whether A) the input is loaded as aword with the relevent bytes masked-off, or B) the input is loadedone byte at a time.While at it, improve debuggability of the internal hash state.Discussion:https://postgr.es/m/CANWCAZZpuV1mES1mtSpAq8tWJewbrv4gEz6R_k4gzNG8GZ5gag%40mail.gmail.com
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+39
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1 file changed

+39
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‎src/include/common/hashfn_unstable.h

Lines changed: 39 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -131,9 +131,6 @@ fasthash_combine(fasthash_state *hs)
131131
{
132132
hs->hash ^=fasthash_mix(hs->accum,0);
133133
hs->hash *=0x880355f21e6d1965;
134-
135-
/* reset hash state for next input */
136-
hs->accum=0;
137134
}
138135

139136
/* accumulate up to 8 bytes of input and combine it into the hash */
@@ -142,9 +139,44 @@ fasthash_accum(fasthash_state *hs, const char *k, size_t len)
142139
{
143140
uint32lower_four;
144141

145-
Assert(hs->accum==0);
146142
Assert(len <=FH_SIZEOF_ACCUM);
143+
hs->accum=0;
147144

145+
/*
146+
* For consistency, bytewise loads must match the platform's endianness.
147+
*/
148+
#ifdefWORDS_BIGENDIAN
149+
switch (len)
150+
{
151+
case8:
152+
memcpy(&hs->accum,k,8);
153+
break;
154+
case7:
155+
hs->accum |= (uint64)k[6] <<8;
156+
/* FALLTHROUGH */
157+
case6:
158+
hs->accum |= (uint64)k[5] <<16;
159+
/* FALLTHROUGH */
160+
case5:
161+
hs->accum |= (uint64)k[4] <<24;
162+
/* FALLTHROUGH */
163+
case4:
164+
memcpy(&lower_four,k,sizeof(lower_four));
165+
hs->accum |= (uint64)lower_four <<32;
166+
break;
167+
case3:
168+
hs->accum |= (uint64)k[2] <<40;
169+
/* FALLTHROUGH */
170+
case2:
171+
hs->accum |= (uint64)k[1] <<48;
172+
/* FALLTHROUGH */
173+
case1:
174+
hs->accum |= (uint64)k[0] <<56;
175+
break;
176+
case0:
177+
return;
178+
}
179+
#else
148180
switch (len)
149181
{
150182
case8:
@@ -175,6 +207,7 @@ fasthash_accum(fasthash_state *hs, const char *k, size_t len)
175207
case0:
176208
return;
177209
}
210+
#endif
178211

179212
fasthash_combine(hs);
180213
}
@@ -288,7 +321,8 @@ fasthash_accum_cstring(fasthash_state *hs, const char *str)
288321
if (PointerIsAligned(str,uint64))
289322
{
290323
len=fasthash_accum_cstring_aligned(hs,str);
291-
Assert(hs_check.hash==hs->hash&&len_check==len);
324+
Assert(len_check==len);
325+
Assert(hs_check.hash==hs->hash);
292326
returnlen;
293327
}
294328
#endif/* SIZEOF_VOID_P */

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