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Fix #625 - no fancy mixing in number hasing

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Just hash upper 32 bits with lower 32 bits. Trying to get too fancy
was causing slowdowns in very trivial cases. Assuming that all
combinations of 64 bits in a double are equally likely (suspect but
probably not that incorrect), the obvious method of xoring the top
32 bits with the lower 32 bits gives a uniform distribution.
This commit is contained in:
Calvin Rose 2021-02-04 19:37:11 -06:00
parent 54c66ecfc0
commit b168b0758a
1 changed files with 4 additions and 12 deletions
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16
src/core/value.c
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@ -307,18 +307,10 @@ int32_t janet_hash(Janet x) {
hash = janet_struct_hash(janet_unwrap_struct(x));
break;
case JANET_NUMBER: {
double num = janet_unwrap_number(x);
if (isnan(num) || isinf(num) || num == 0) {
hash = 0;
} else {
hash = (int32_t)num;
hash = ((hash >> 16) ^ hash) * 0x45d9f3b;
hash = ((hash >> 16) ^ hash) * 0x45d9f3b;
hash = (hash >> 16) ^ hash;
uint32_t lo = (uint32_t)(janet_u64(x) & 0xFFFFFFFF);
hash ^= lo + 0x9e3779b9 + (hash << 6) + (hash >> 2);
}
uint64_t i = janet_u64(x);
uint32_t lo = (uint32_t)(i & 0xFFFFFFFF);
uint32_t hi = (uint32_t)(i >> 32);
hash = (int32_t)(hi ^ (lo >> 3));
break;
}
case JANET_ABSTRACT: {