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

do not redefine rewind

more memory errors (valgrind)

sync with plan 9

Remove debugging print.

Fix rc not to bus error on Mac OS X. Don't print about child notes either.

Plan 9's rc. not a clear win over byron's, but at least it has the right syntax.