I want my FPE!
Dave Korn
dave.korn.cygwin@googlemail.com
Thu Sep 17 20:22:00 GMT 2009
Mark Geisert wrote:
> Is there something I need to do to "condition" the Cygwin environment to
> generate FP exceptions? I saw the code in winsup/something/or/other to map x86
> FP exceptions to SIGFPE but it seems somehow the exceptions aren't being
> generated in the first place.
Very possibly not. There's probably a bit in the FPUCW you need to set or
something. Ah, yes: see winsup/cygwin/crt0.c:
> /* In the following ifdef'd i386 code, the FPU precision is set to 80 bits
> and all FPU exceptions are masked. The former is needed to make long
> doubles work correctly. The latter causes the FPU to generate NaNs and
> Infinities instead of signals for certain operations.
> */
> #define FPU_RESERVED 0xF0C0
> #define FPU_DEFAULT 0x033f
> {
> volatile unsigned short cw;
>
> /* Get Control Word */
> __asm__ volatile ("fnstcw %0" : "=m" (cw) : );
>
> /* mask in */
> cw &= FPU_RESERVED;
> cw |= FPU_DEFAULT;
>
> /* set cw */
> __asm__ volatile ("fldcw %0" :: "m" (cw));
> }
You can copy and paste that hunk into your own main() and change the
constants to anything you like.
cheers,
DaveK
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