http://d.puremagic.com/issues/show_bug.cgi?id=5386
Summary: Initialising out float parameter causes FPU exception
Product: D
Version: D2
Platform: x86
OS/Version: Windows
Status: NEW
Severity: normal
Priority: P2
Component: DMD
AssignedTo: [email protected]
ReportedBy: [email protected]
--- Comment #0 from Peter Moore <[email protected]> 2010-12-28 04:50:04 PST
---
The following short code snippet causes slow code caused by FPU exception:
float f;
func(f);
void func(out float ff) {
ff = 1;
}
The following code is produced for the function:
func LABEL NEAR
push ebp
mov ebp, esp
push eax
fld dword ptr [_nan]
fstp dword ptr [eax]
fld dword ptr [_one]
fstp dword ptr [eax]
mov esp, ebp
pop ebp
ret
It appears that in DMD2 a float NaN is 0x7FE00000 (in dword format) but when it
initialises a float 'out' parameter it
initialises it with 0x7FA00000. This causes an FPU trap which unnecessarily
eats up around 250 ticks.
I had a quick look at doubles too. This uses 7FF4000000000000 to initialise a
double out parameter which also traps the FPU.
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