Status: Accepted
Owner: [email protected]
Labels: Type-Bug Priority-Medium
New issue 3477 by [email protected]: Math.floor(-0) returns the wrong
result when V8 is compiled with MSVC 10.0 with /arch:SSE2
http://code.google.com/p/v8/issues/detail?id=3477
Math.floor(-0) returns 0 instead of -0.
The reason is that the runtime function is implemented using std::floor,
which is compiled to the following sequence by MSVC 10.0, if SSE2 is
enabled and the build target is release mode ia32.
00BF8E8B movsd xmm2,mmword ptr [eax+3] <-- load from heap number
00BF8E90 int 3 <-- debug break
00BF8E91 test byte ptr [$S1 (0ED4A58h)],1
00BF8E98 movsd xmm5,mmword ptr [__real@8000000000000000 (0D801A8h)]
00BF8EA0 movsd xmm1,mmword ptr [__real@4330000000000000 (0D801C0h)]
00BF8EA8 movsd xmm4,mmword ptr [__real@3ff0000000000000 (0D866A0h)]
00BF8EB0 movapd xmm0,xmm5
00BF8EB4 andpd xmm0,xmm2
00BF8EB8 movapd xmm3,xmm0
00BF8EBC movapd xmm0,xmm2
00BF8EC0 xorpd xmm0,xmm3
00BF8EC4 cmpltsd xmm0,xmm1
00BF8EC9 andpd xmm1,xmm0
00BF8ECD orpd xmm1,xmm3
00BF8ED1 movapd xmm0,xmm2
00BF8ED5 addsd xmm0,xmm1 <--
00BF8ED9 subsd xmm0,xmm1
00BF8EDD movapd xmm1,xmm0
00BF8EE1 subsd xmm1,xmm2
00BF8EE5 cmpnlesd xmm1,xmm3
00BF8EEA andpd xmm1,xmm4
00BF8EEE subsd xmm0,xmm1
At the addsd instruction, -0 is added to 0, which removes the sign. The
final result is 0, which is wrong.
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