Merge branch 'egil/fix-hash-float-zero/OTP-12641'

* egil/fix-hash-float-zero/OTP-12641:
  erts: Ensure hashing of zero is consistent

2 files changed, 44 insertions, 12 deletions

diff --git a/erts/emulator/beam/utils.c b/erts/emulator/beam/utils.c
index bf6d9fff50..aecfe04a75 100644
--- a/erts/emulator/beam/utils.c
+++ b/erts/emulator/beam/utils.c
@@ -955,12 +955,14 @@ tail_recur:
 	UINT32_HASH_RET(external_ref_numbers(term)[0],FUNNY_NUMBER9,FUNNY_NUMBER10);
     case FLOAT_DEF: 
 	{
-	    FloatDef ff;
-	    GET_DOUBLE(term, ff);
-	    hash = hash*FUNNY_NUMBER6 + (ff.fw[0] ^ ff.fw[1]);
-	    break;
+            FloatDef ff;
+            GET_DOUBLE(term, ff);
+            if (ff.fd == 0.0f) {
+                ff.fd = 0.0f; /* ensure pos. 0.0 */
+            }
+            hash = hash*FUNNY_NUMBER6 + (ff.fw[0] ^ ff.fw[1]);
+            break;
 	}
-
     case MAKE_HASH_CDR_PRE_OP:
 	term = (Eterm) WSTACK_POP(stack);
 	if (is_not_list(term)) {
@@ -1474,6 +1476,9 @@ make_hash2(Eterm term)
 	    {
 		FloatDef ff;
 		GET_DOUBLE(term, ff);
+                if (ff.fd == 0.0f) {
+                    ff.fd = 0.0f; /* ensure pos. 0.0 */
+                }
 #if defined(WORDS_BIGENDIAN) || defined(DOUBLE_MIDDLE_ENDIAN)
 		UINT32_HASH_2(ff.fw[0], ff.fw[1], HCONST_12);
 #else
@@ -1893,8 +1898,8 @@ make_internal_hash(Eterm term)
 	    {
 		FloatDef ff;
 		GET_DOUBLE(term, ff);
-                if (ff.fd == 0.0) {
-                    ff.fd = 0.0; /* ensure pos. 0.0 */
+                if (ff.fd == 0.0f) {
+                    ff.fd = 0.0f; /* ensure pos. 0.0 */
                 }
 		UINT32_HASH_2(ff.fw[0], ff.fw[1], HCONST_12);
 		goto pop_next;
@@ -2079,12 +2084,14 @@ tail_recur:
 	break;
     case FLOAT_DEF: 
 	{
-	    FloatDef ff;
-	    GET_DOUBLE(term, ff);
-	    hash = hash*FUNNY_NUMBER6 + (ff.fw[0] ^ ff.fw[1]);
+            FloatDef ff;
+            GET_DOUBLE(term, ff);
+            if (ff.fd == 0.0f) {
+                ff.fd = 0.0f; /* ensure pos. 0.0 */
+            }
+            hash = hash*FUNNY_NUMBER6 + (ff.fw[0] ^ ff.fw[1]);
 	}
 	break;
-
     case MAKE_HASH_CDR_PRE_OP:
 	term = (Eterm) WSTACK_POP(stack);
 	if (is_not_list(term)) {
diff --git a/erts/emulator/test/hash_SUITE.erl b/erts/emulator/test/hash_SUITE.erl
index 647bb45049..5fa45f772d 100644
--- a/erts/emulator/test/hash_SUITE.erl
+++ b/erts/emulator/test/hash_SUITE.erl
@@ -73,6 +73,7 @@ config(priv_dir,_) ->
 	 init_per_group/2,end_per_group/2,
 	 test_basic/1,test_cmp/1,test_range/1,test_spread/1,
 	 test_phash2/1,otp_5292/1,bit_level_binaries/1,otp_7127/1,
+         test_hash_zero/1,
 	 end_per_testcase/2,init_per_testcase/2]).
 init_per_testcase(_Case, Config) ->
     Dog=test_server:timetrap(test_server:minutes(10)),
@@ -86,7 +87,9 @@ suite() -> [{ct_hooks,[ts_install_cth]}].
 
 all() -> 
     [test_basic, test_cmp, test_range, test_spread,
-     test_phash2, otp_5292, bit_level_binaries, otp_7127].
+     test_phash2, otp_5292, bit_level_binaries, otp_7127,
+     test_hash_zero
+    ].
 
 groups() -> 
     [].
@@ -160,6 +163,8 @@ otp_7127(doc) ->
 otp_7127(Config) when is_list(Config) ->
     otp_7127_test().
 
+test_hash_zero(Config) when is_list(Config) ->
+    hash_zero_test().
 -endif.
 
 
@@ -591,6 +596,26 @@ otp_7127_test() ->
     38990304 = erlang:phash2(<<"Scott9">>),
     ok.
 
+hash_zero_test() ->
+    Zs = [0.0, -0.0, 0/-1, 0.0/-1, 0/-(1 bsl 65),
+          binary_to_term(<<131,70,0,0,0,0,0,0,0,0>>),    %% +0.0
+          binary_to_term(<<131,70,128,0,0,0,0,0,0,0>>)], %% -0.0
+    ok = hash_zero_test(Zs,fun(T) -> erlang:phash2(T, 1 bsl 32) end),
+    ok = hash_zero_test(Zs,fun(T) -> erlang:phash(T, 1 bsl 32) end),
+    ok = hash_zero_test(Zs,fun(T) -> erlang:hash(T, (1 bsl 27) - 1) end),
+    ok.
+
+hash_zero_test([Z|Zs],F) ->
+    hash_zero_test(Zs,Z,F(Z),F).
+hash_zero_test([Z|Zs],Z0,V,F) ->
+    true = Z0 =:= Z, %% assert exact equal
+    Z0   = Z,        %% assert matching
+    V    = F(Z),     %% assert hash
+    hash_zero_test(Zs,Z0,V,F);
+hash_zero_test([],_,_,_) ->
+    ok.
+
+
 %%
 %% Reference implementation of integer hashing
 %%