From 442c9b4d11a62c55b46ffb25f27b5ec5fb3adda7 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Wed, 11 Feb 2015 21:50:25 +0100
Subject: erts: First recursive version of hashmap compare

---
 erts/emulator/beam/erl_hashmap.c | 129 +++++++++++++++++++++++++++++++++++++++
 erts/emulator/beam/erl_hashmap.h |   2 +
 erts/emulator/beam/utils.c       |  13 ++++
 3 files changed, 144 insertions(+)

(limited to 'erts')

diff --git a/erts/emulator/beam/erl_hashmap.c b/erts/emulator/beam/erl_hashmap.c
index 2e3a4b8982..2fd743a2d8 100644
--- a/erts/emulator/beam/erl_hashmap.c
+++ b/erts/emulator/beam/erl_hashmap.c
@@ -1112,6 +1112,135 @@ static Eterm hashmap_values(Process* p, Eterm node) {
     return res;
 }
 
+static int hash_cmp(Uint32 ha, Uint32 hb)
+{
+    int i;
+    for (i=0; i<8; i++) {
+	int cmp = (int)(ha & 0xF) - (int)(hb & 0xF);
+	if (cmp)
+	    return cmp;
+	ha >>= 4;
+	hb >>= 4;
+    }
+    return 0;
+}
+
+static int key_hash_cmp(Eterm* ap, Eterm* bp)
+{
+    Eterm th[2];
+    unsigned lvl = 0;
+
+    if (ap && bp) {
+	ASSERT(CMP_TERM(CAR(ap), CAR(bp)) != 0);
+	for (;;) {
+	    Uint32 ha = hashmap_restore_hash(th, lvl, CAR(ap));
+	    Uint32 hb = hashmap_restore_hash(th, lvl, CAR(bp));
+	    int cmp = hash_cmp(ha, hb);
+	    if (cmp)
+		return cmp;
+	    lvl += 8;
+	}
+    }
+    return ap ? -1 : 1;
+}
+
+int hashmap_cmp(Eterm a, Eterm b)
+{
+    DECLARE_WSTACK(astack);
+    DECLARE_WSTACK(bstack);
+    Eterm *ap;
+    Eterm *bp;
+    Eterm min_key;
+    int cmp_res = 0;
+
+    /* Strategy:
+       Phase 1.
+          While keys are identical
+	  Do synchronous stepping through leafs of both trees in hash order.
+          Maintain min value of min key.
+
+       Phase 2:  (If key diff was found in phase 1)
+          Ignore values from now on.
+          Continue iterate trees by always advancing the one lagging behind hash-wise.
+          Identical keys are skipped
+          A minimal key can only be candidate as tie-breaker if we have passed
+          that hash value in the other tree (which means the key did not exist
+          in the other tree).
+     */
+
+    hashmap_iterator_init(&astack, a);
+    hashmap_iterator_init(&bstack, b);
+
+    for (;;) {   /* Phase 1 */
+	int cmp;
+	ap = hashmap_iterator_next(&astack);
+	bp = hashmap_iterator_next(&bstack);
+	if (!ap) {
+	    ASSERT(!bp);
+	    return cmp_res;
+	}
+	cmp = CMP_TERM(CAR(ap), CAR(bp));
+	if (cmp)
+	    break;
+
+	/* No key diff found so far, compare values */
+	if (!cmp_res || (CMP_TERM(CAR(ap), min_key) < 0)) {
+	    cmp = CMP(CDR(ap), CDR(bp));
+	    if (cmp) {
+		cmp_res = cmp;
+		min_key = CAR(ap);
+	    }
+	}
+    }
+
+    /* Phase 2 */
+
+    if (key_hash_cmp(ap,bp) < 0) {
+	min_key = CAR(ap);
+	cmp_res = -1;
+	ap = hashmap_iterator_next(&astack);
+    }
+    else {
+	min_key = CAR(bp);
+	cmp_res = 1;
+	bp = hashmap_iterator_next(&bstack);
+    }
+
+    for (;;) {
+	int hash_cmp;
+
+	while (ap && bp && CMP_TERM(CAR(ap), CAR(bp)) == 0) {
+	    ap = hashmap_iterator_next(&astack);
+	    bp = hashmap_iterator_next(&bstack);
+	}
+	if (!ap && !bp)
+	    break;
+
+	hash_cmp = key_hash_cmp(ap,bp);
+	if (hash_cmp < 0) {
+	    ASSERT(ap);
+	    if (CMP_TERM(CAR(ap), min_key) < 0) {
+		min_key = CAR(ap);
+                cmp_res = -1;
+	    }
+	    ap = hashmap_iterator_next(&astack);
+	}
+	else if (hash_cmp > 0) {
+	    ASSERT(bp);
+	    if (CMP_TERM(CAR(bp), min_key) < 0) {
+		min_key = CAR(bp);
+		cmp_res = 1;
+	    }
+	    bp = hashmap_iterator_next(&bstack);
+	}
+    }
+
+    DESTROY_WSTACK(astack);
+    DESTROY_WSTACK(bstack);
+
+    return cmp_res;
+}
+
 /* hashmap:info/0 */
 
 static Eterm hashmap_info(Process *p, Eterm node) {
diff --git a/erts/emulator/beam/erl_hashmap.h b/erts/emulator/beam/erl_hashmap.h
index 4ef795b11e..4a4163bce9 100644
--- a/erts/emulator/beam/erl_hashmap.h
+++ b/erts/emulator/beam/erl_hashmap.h
@@ -24,11 +24,13 @@
 #include "sys.h"
 
 Eterm erts_hashmap_get(Eterm key, Eterm map);
+int hashmap_cmp(Eterm a, Eterm b);
 
 /* erl_term.h stuff */
 #define make_hashmap(x)		make_boxed((Eterm*)(x))
 #define make_hashmap_rel 	make_boxed_rel
 #define is_hashmap(x)		(is_boxed((x)) && is_hashmap_header(*boxed_val((x))))
+#define is_hashmap_rel(RTERM,BASE)  is_hashmap(rterm2wterm(RTERM,BASE))
 #define is_hashmap_header(x)	(((x) & (_TAG_HEADER_MASK)) == _TAG_HEADER_HASHMAP)
 #define hashmap_val(x)		_unchecked_boxed_val((x))
 #define hashmap_val_rel(RTERM, BASE) hashmap_val(rterm2wterm(RTERM, BASE))
diff --git a/erts/emulator/beam/utils.c b/erts/emulator/beam/utils.c
index 908116c64c..9fd53e941d 100644
--- a/erts/emulator/beam/utils.c
+++ b/erts/emulator/beam/utils.c
@@ -2702,6 +2702,19 @@ tailrecur_ne:
 		    goto tailrecur;
 		}
 
+	    case (_TAG_HEADER_HASHMAP >> _TAG_PRIMARY_SIZE) :
+		{
+		    if (!is_hashmap_rel(b,b_base)) {
+			a_tag = HASHMAP_DEF;
+			goto mixed_types;
+		    }
+		    i = (((hashmap_head_t*) hashmap_val_rel(a,a_base))->size -
+			 ((hashmap_head_t*) hashmap_val_rel(b,b_base))->size);
+		    if (i) {
+			RETURN_NEQ(i);
+		    }
+		    ON_CMP_GOTO(hashmap_cmp(a, b));
+		}
 	    case (_TAG_HEADER_FLOAT >> _TAG_PRIMARY_SIZE):
 		if (!is_float_rel(b,b_base)) {
 		    a_tag = FLOAT_DEF;
-- 
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