How to force floating point exceptions to dump core
Chris Wagner
jwag at moose.sgi.com
Fri May 4 01:52:07 AEST 1990
In article <1521 at merlin.bhpmrl.oz>, tim at merlin.bhpmrl.oz (Tim Monks) writes:
> How do you force floating point exceptions to dump core in C on an SG ?
>
> The reason I want to do this is I've got a longish program which
> generates NaN's somewhere. I thought the easiest way to track
> down the problem was to set up an exception handler which would
> capture SIGFPE signals and take appropriate action. I didn't manage
> to get even that far, I couldn't even make the program baulk at NaN's.
>
>
> I've tried some variations on the following with no success:
>
> --8<----------------------------------------------------------------------
> #include <stdio.h>
> #include <math.h>
> #include <signal.h>
> #include <fp_class.h>
>
> main(argc, argv)
>
> int argc;
> char **argv;
>
> {
>
> void Report_class(double);
> double x,zero;
>
>
> /* set up a signal trap */
> signal(SIGFPE, SIG_DFL);
>
>
> /* try to trap Infinity */
> zero = 0.0;
> x = 1.0/zero;
>
> /*
> I wanted the program to dump core on the previous line,
> but it carried on, so we have a look at what we got.
> */
> Report_class(x);
>
>
> /* Now try to trap NaN */
> x = zero/zero;
> Report_class(x);
> }
>
>
>
> void Report_class(double x)
> {
> int type;
>
> type = fp_class_d(x);
> if (type == FP_SNAN)
> fprintf(stderr,"X = %lf is a signalling NaN\n",x);
> else if (type == FP_QNAN)
> fprintf(stderr,"X = %lf is a quiet NaN\n",x);
> else if (type == FP_POS_INF)
> fprintf(stderr,"X = %lf is positive infinity\n",x);
> else if (type == FP_NEG_INF)
> fprintf(stderr,"X = %lf is negative infinity\n",x);
> else
> fprintf(stderr,"X = %lf is something quite different !!!\n",x);
> }
> --8<----------------------------------------------------------------------
>
> And the program gives the following output: (240GTX, Irix 3.2.2)
> X = Infinity is positive infinity
> X = NaN is a quiet NaN
> but definitely no core!
>
> How do you make quiet NaN's noisy ? (a signaling NaN)
>
> I've RTFM, but haven't found any enlightenment on this. Can someone
> point me at the relevant FM to read, or provide a solution.
>
> On this topic, how does SG propagate NaN's and Infinity through
> arithmetic and math library operations ?
>
>
> I'll post a summary if there's any demand for one.
>
> Thanks in advance.
> --
> Dr. Tim Monks
>
> Image Processing & Data Analysis Group | (direct) (+61-3)566-7448
> BHP Melbourne Research Laboratories | (switch) (+61-3)560-7066
> 245 Wellington Rd, Mulgrave, 3170, | (fax) (+61-3)561-6709
> AUSTRALIA | (EMAIL) tim at merlin.bhpmrl.oz.au
Try including and calling the following function:
#include <asm.h>
#include <regdef.h>
#include <sys/fpu.h>
.globl fpe_enable
.ent fpe_enable
fpe_enable:
cfc1 t0, fpc_csr # grab fpu status register
li t1, 0xF10
/*li t1, 0x3f000*/
or t0, t0, t1 # or in enable bits
ctc1 t0, fpc_csr # replace fpu status
j ra # return
.end fpe_enable
By default the C runtime startup does not enable floating point exceptions
In our next release a complete fp exception package has been added
Chris Wagner
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