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Code Issues 1 Releases Wiki Activity

Add some more changes to hashing to improve pointer hashing.

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
View File

@ -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;
}

24
tools/hashbench/ints1.janet Normal file
View File

@ -0,0 +1,24 @@
(def f @{})
(var collisions 0)
(loop [x :range [0 300] y :range [0 300]]
(def key (hash (+ (* x 1000) y)))
(if (in f key)
(++ collisions))
(put f key true))
(print "ints 1 collisions: " collisions)
(def f @{})
(var collisions 0)
(loop [x :range [100000 101000] y :range [100000 101000]]
(def key (hash [x y]))
(if (in f key) (++ collisions))
(put f key true))
(print "int pair 1 collisions: " collisions)
(def f @{})
(var collisions 0)
(loop [x :range [10000 11000] y :range [10000 11000]]
(def key (hash [x y]))
(if (in f key) (++ collisions))
(put f key true))
(print "int pair 2 collisions: " collisions)