Date: Thu, 5 Dec 1996 14:06:38 +0100 (MET)
Message-Id: <1.5.4.16.19961205141128.1bf7bcf4@um2gess0.ges.univ-montp2.fr>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
To: djgpp AT delorie DOT com
From: Michel Julier <julier AT GES DOT univ-montp2 DOT fr>
Subject: bug in exp() in JDGPP v2.0

There seems to be a bug in the exp() function: on my computer,
for certain values it will push an unexpected "-1" in the numerical processor
stack, so coming on calculations will be likely to crash.
I saw that by using FSDB.exe (Full Screen DeBugger from GNU) for PC-MSDOS.
I guess the exp() function is part of the DJGPP package, so I am sending
the report to you.

Thanks in advance.

-------------------------------------
	Michel JULIER
Groupe d'Etudes des Semiconducteurs, CC074, place Eugene Bataillon,
  34095 Montpellier Cedex 5, FRANCE, tel. +33 4 67 14 32 39
Chez moi/at home/a casa: 13 rue de l'Ecole de Droit, 
  34000 Montpellier, FRANCE, tel. +33 4 67 92 95 67

The example program follows
---------------------------------
/* This programs fails to run when compiled with   gcc -Wall -g test.c -o
test -lm
   on a PC - Cyrix P133+ at 110MHz - MSDOS 6.20 + Windows 3.1

I am using DJGPP v2.0 in a MS-DOS Command window

---Transcript of error messages ---

C:\USERS\JULIER>test
Exiting due to signal SIGFPE
Floating Point exception at eip=00001e35
eax=00000002 ebx=000500c0 ecx=0005304c edx=00000033 esi=00000054 edi=0000dec0
ebp=0004de98 esp=0004de18 cs=00af ds=00b7 fs=0087 gs=00c7 ss=00b7
Call frame traceback EIPs:
  0x00001e35  (_main+2293, line 52 of test.c)  [see "ERROR HAPPENS HERE"]
  0x00004213  (___crt1_startup+115)

C:\USERS\JULIER>symify test
Exiting due to signal SIGFPE
Floating Point exception at eip=000057f2
eax=00000000 ebx=00000000 ecx=0005404c edx=00000033 esi=0004f3a8 edi=0000f5e0
ebp=0004f5c4 esp=0004f3a8 cs=00af ds=00b7 fs=0087 gs=00c7 ss=00b7
Call frame traceback EIPs:
  0x000057f2  (_realloc+126)
  0x000039ba  (___kernal_standard+3788)

C:\USERS\JULIER>symify test

C:\USERS\JULIER>_
  
*/ 

#include <stdio.h>
#include <math.h>
#define chose(a,b) ((a)+(b))/((a)-(b))
#define chose2(a,b) chose(((a)*(b)),((a)/(b)))
#define chose3(a,b) chose2(((a)*(b)),((a)/(b)))
#define chose4(a,b) chose3(((a)*(b)),((a)/(b)))
#define chose5(a,b) chose4(((a)*(b)),((a)/(b)))
#define chose6(a,b) chose5(((a)*(b)),((a)/(b)))
#define chose7(a,b) chose6(((a)*(b)),((a)/(b)))
#define chose8(a,b) chose7(((a)*(b)),((a)/(b)))
#define chose9(a,b) chose8(((a)*(b)),((a)/(b)))


void main(){
	double a,b;
	double x=1.1,y=1.2;
	
	a=-0.482636;
	b=exp(a); /* This produces a remaining -1 in the numerical processor stack */
            /* No problem any more if you remove this line */             
	b=chose9(x,y);  /* ERROR HAPPENS HERE:
	                This will try to use all the stack for the calculation.  */
	printf("%g\n",b);
}