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author | Xi Wang <xi.wang@gmail.com> | 2013-03-19 14:36:50 -0400 |
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committer | Russ Cox <rsc@swtch.com> | 2013-03-19 14:36:50 -0400 |
commit | 1bfec89b997c9544100128fec6e0b0c3757fdd11 (patch) | |
tree | 933faa410c29279f965b8218117ae91f8a7dc844 /src/libsunrpc/prog.c | |
parent | 8a2a5b8f2568a665f00741994c1247f0f7d3dffe (diff) | |
download | plan9port-1bfec89b997c9544100128fec6e0b0c3757fdd11.tar.gz plan9port-1bfec89b997c9544100128fec6e0b0c3757fdd11.tar.bz2 plan9port-1bfec89b997c9544100128fec6e0b0c3757fdd11.zip |
rc: avoid undefined C
There are two bugs in pdec() on INT_MIN:
* wrong output.
`n = 1-n' should be `n = -1-n' when n is INT_MIN.
* infinite loop.
gcc optimizes `if(n>=0)' into `if(true)' because `-INT_MIN' (signed integer overflow) is undefined behavior in C, and gcc assumes the negation of a negative number must be positive. The resulting binary keeps printing '-' forever given INT_MIN.
Try the simplified pdec.c below.
$ gcc pdec.c
$ ./a.out -2147483648
--214748364*
$ gcc pdec.c -O2
$ ./a.out -2147483648
<infinite loop>
$ gcc pdec.c -O2 -D__PATCH__
$ ./a.out -2147483648
-2147483648
=== pdec.c ===
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#define io void
void pchr(io *f, int c)
{
putchar(c);
}
void pdec(io *f, int n)
{
if(n<0){
#ifndef __PATCH__
n=-n;
if(n>=0){
pchr(f, '-');
pdec(f, n);
return;
}
/* n is two's complement minimum integer */
n = 1-n;
#else
if(n!=INT_MIN){
pchr(f, '-');
pdec(f, -n);
return;
}
/* n is two's complement minimum integer */
n = -(INT_MIN+1);
#endif
pchr(f, '-');
pdec(f, n/10);
pchr(f, n%10+'1');
return;
}
if(n>9)
pdec(f, n/10);
pchr(f, n%10+'0');
}
int main(int argc, char **argv)
{
int n = atoi(argv[1]);
pdec(NULL, n);
putchar('\n');
}
R=rsc
CC=plan9port.codebot
https://codereview.appspot.com/7241055
Diffstat (limited to 'src/libsunrpc/prog.c')
0 files changed, 0 insertions, 0 deletions