DevOps, CI/CD and Automation

Hi,

I encountered a problem related to some functions provided by math library on sun. I narrowed it down to the following test program:

========================================================
#include<stdio.h>
#include<math.h>

void pow_res()
{
double x = 10.0;
double y = 2.5;

printf("pow(%.2e, %.2e):%.20e\n", x, y, pow(10.0, 2.5));
}

void cos_res()
{
double x = -6.433230338433114370e-02;

printf("x:%.20e cos(x):%.20e\n", x, cos(x));
}

int main()
{
pow_res();
cos_res();
return 0;
}
========================================================

The above test program has to be linked with any math library. It is �libm� for amd64/linux, but for sparc we have choice between �libm� and �libmopt�. I am compiling above program with "cc <test_program.c> <-lm/-lmopt>" command.

On sparc, if the above test program is getting linked with �-lm" then it gives same results for the �cos� on both amd64 and sparc, but gives different results (16th decimal digit onward) for �pow�. If it is getting linked with �-lmopt� then it gives same result for the �pow� on both the platforms, but gives different results for �cos�. Linux results match with the amd64 results.

The �Numerical Computation Guide� provided by SUN (ftp://docs-pdf.sun.com/802-5692/802-5692.pdf page 40, table 2.10 ) says that you can trust only 15-17 decimal digits for double calculation. But here the requirement is to match the sparc results exactly with the amd64/linux or at least match the result till 20th decimal digit. I guess it is something to do with the FPU setting either through compiler options or code. I tried many different compiler options, like -fast, different combinations of compiler options provided by -fast macro, but nothing helped.

Following is the system configuration:
Amd64:
gcc version: 3.3.6
OS: RedHat Enterprise Linux 3.0 U7 (Linux 2.4.21-40.ELsmp x86_64)

Sparc:
cc version: Sun C 5.8 Patch 121015-01
OS: SunOS 5.9 Generic_118558-21 sun4u sparc SUNW,Sun-Fire-280R

It will be great if somebody can explain the problem and the solution to get rid of it.

Many thanks,
Sunil