#include "scan.h" static const unsigned long maxlong = ((unsigned long)-1)>>1; size_t scan_longn(const char *src,size_t n,long *dest) { register const char *tmp; register long int l; register unsigned char c; unsigned int neg; int ok; if (!n--) return 0; tmp=src; l=0; ok=0; neg=0; switch (*tmp) { case '-': neg=1; /* fall through */ case '+': ++tmp; } while (n-->0 && (c=(unsigned char)(*tmp-'0'))<10) { unsigned long int n; #if defined(__GNUC__) && (__GNUC__ >= 5) if (__builtin_mul_overflow(l,10,&n) || __builtin_add_overflow(n,c,&n)) break; #else /* we want to do: l=l*10+c * but we need to check for integer overflow. * to check whether l*10 overflows, we could do * if ((l*10)/10 != l) * however, multiplication and division are expensive. * so instead of *10 we do (l<<3) (i.e. *8) + (l<<1) (i.e. *2) * and check for overflow on all the intermediate steps */ n=(unsigned long)l<<3; if ((n>>3)!=(unsigned long)l) break; if (n+((unsigned long)l<<1) < n) break; n+=(unsigned long)l<<1; if (n+c < n) break; n+=c; #endif if (n > maxlong+neg) break; l=(long)n; ++tmp; ok=1; } if (!ok) return 0; *dest=(neg?-l:l); return (size_t)(tmp-src); }