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authorSverker Eriksson <[email protected]>2017-04-28 14:41:25 +0200
committerSverker Eriksson <[email protected]>2017-04-28 14:41:25 +0200
commit28d64608d9f9e1d86d34323d1d1646ab17278d64 (patch)
tree000af517b27d59e51bf02928924a5088e23a7d8e
parent156542f6c8d5c98013fec1eb3c9359fc245f20fc (diff)
parent3684673aab9006d114db4298ab882805bf9bf657 (diff)
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Merge branch 'sverker/internal-hash-opt'
-rw-r--r--erts/emulator/beam/utils.c43
1 files changed, 6 insertions, 37 deletions
diff --git a/erts/emulator/beam/utils.c b/erts/emulator/beam/utils.c
index 9263798a28..cdf766b206 100644
--- a/erts/emulator/beam/utils.c
+++ b/erts/emulator/beam/utils.c
@@ -1581,9 +1581,6 @@ Uint32
make_internal_hash(Eterm term)
{
Uint32 hash;
- Uint32 hash_xor_pairs;
-
- ERTS_UNDEF(hash_xor_pairs, 0);
/* Optimization. Simple cases before declaration of estack. */
if (primary_tag(term) == TAG_PRIMARY_IMMED1) {
@@ -1664,6 +1661,11 @@ make_internal_hash(Eterm term)
Eterm* ptr = boxed_val(term) + 1;
Uint size;
int i;
+
+ /*
+ * We rely on key-value iteration order being constant
+ * for identical maps (in this VM instance).
+ */
switch (hdr & _HEADER_MAP_SUBTAG_MASK) {
case HAMT_SUBTAG_HEAD_FLATMAP:
{
@@ -1675,26 +1677,10 @@ make_internal_hash(Eterm term)
if (size == 0)
goto pop_next;
- /* We want a hash function that is *independent* of
- * the order in which keys and values are encountered.
- * We therefore calculate context independent hashes for all .
- * key-value pairs and then xor them together.
- *
- * We *do* need to use an initial seed for each pair, i.e. the
- * hash value, so the hash value is reset for each pair with 'hash'.
- * If we don't, no additional entropy is given to the system and the
- * hash collision resolution in maps:from_list/1 would fail.
- */
- ESTACK_PUSH(s, hash_xor_pairs);
- ESTACK_PUSH(s, hash);
- ESTACK_PUSH(s, HASH_MAP_TAIL);
for (i = size - 1; i >= 0; i--) {
- ESTACK_PUSH(s, hash); /* initial seed for all pairs */
- ESTACK_PUSH(s, HASH_MAP_PAIR);
ESTACK_PUSH(s, vs[i]);
ESTACK_PUSH(s, ks[i]);
}
- hash_xor_pairs = 0;
goto pop_next;
}
case HAMT_SUBTAG_HEAD_ARRAY:
@@ -1703,10 +1689,6 @@ make_internal_hash(Eterm term)
UINT32_HASH(size, HCONST_16);
if (size == 0)
goto pop_next;
- ESTACK_PUSH(s, hash_xor_pairs);
- ESTACK_PUSH(s, hash);
- ESTACK_PUSH(s, HASH_MAP_TAIL);
- hash_xor_pairs = 0;
}
switch (hdr & _HEADER_MAP_SUBTAG_MASK) {
case HAMT_SUBTAG_HEAD_ARRAY:
@@ -1722,8 +1704,6 @@ make_internal_hash(Eterm term)
while (i) {
if (is_list(*ptr)) {
Eterm* cons = list_val(*ptr);
- ESTACK_PUSH(s, hash); /* initial seed for all pairs */
- ESTACK_PUSH(s, HASH_MAP_PAIR);
ESTACK_PUSH(s, CDR(cons));
ESTACK_PUSH(s, CAR(cons));
}
@@ -1739,7 +1719,7 @@ make_internal_hash(Eterm term)
case EXPORT_SUBTAG:
{
Export* ep = *((Export **) (export_val(term) + 1));
- /* Assumes Export entries never moves */
+ /* Assumes Export entries never move */
POINTER_HASH(ep, HCONST_14);
goto pop_next;
}
@@ -1919,17 +1899,6 @@ make_internal_hash(Eterm term)
term = ESTACK_POP(s);
switch (term) {
- case HASH_MAP_TAIL: {
- hash = (Uint32) ESTACK_POP(s);
- UINT32_HASH(hash_xor_pairs, HCONST_19);
- hash_xor_pairs = (Uint32) ESTACK_POP(s);
- goto pop_next;
- }
- case HASH_MAP_PAIR:
- hash_xor_pairs ^= hash;
- hash = (Uint32) ESTACK_POP(s); /* initial seed for all pairs */
- goto pop_next;
-
case HASH_CDR:
CONST_HASH(HCONST_18); /* Hash CDR i cons cell */
goto pop_next;