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Code Issues 1 Releases Wiki Activity

Add some more changes to hashing to improve pointer hashing.

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This commit is contained in:
Calvin Rose
2021-12-07 08:36:08 -06:00
parent 92fdd07ca3
commit 6d9286a202
2 changed files with 31 additions and 5 deletions
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12
src/core/value.c
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@@ -325,7 +325,7 @@ int32_t janet_hash(Janet x) {
uint32_t lo = (uint32_t)(as.u & 0xFFFFFFFF);
uint32_t hi = (uint32_t)(as.u >> 32);
uint32_t hilo = (hi ^ lo) * 2654435769u;
hash = (int32_t)((hilo << 16) | ((hilo >> 16) & 0xFFFF));
hash = (int32_t)((hilo << 16) | (hilo >> 16));
break;
}
case JANET_ABSTRACT: {
@@ -339,15 +339,17 @@ int32_t janet_hash(Janet x) {
/* fallthrough */
default:
if (sizeof(double) == sizeof(void *)) {
/* Assuming 8 byte pointer */
/* Assuming 8 byte pointer (8 byte aligned) */
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));
uint32_t hilo = (hi ^ lo) * 2654435769u;
hash = (int32_t)((hilo << 16) | (hilo >> 16));
} else {
/* Assuming 4 byte pointer (or smaller) */
hash = (int32_t)((char *)janet_unwrap_pointer(x) - (char *)0);
hash >>= 2;
ptrdiff_t diff = ((char *)janet_unwrap_pointer(x) - (char *)0);
uint32_t hilo = (uint32_t) diff * 2654435769u;
hash = (int32_t)((hilo << 16) | (hilo >> 16));
}
break;
}