#include "scan.h" static const unsigned short maxshort = ((unsigned short)-1)>>1; size_t scan_short(const char* src,short* dest) { register const char *tmp; register short l; register unsigned char c; int neg; int ok; tmp=src; l=0; ok=neg=0; switch (*tmp) { case '-': neg=1; /* fall through */ case '+': ++tmp; } while ((c=(unsigned char)(*tmp-'0'))<10) { unsigned short 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 short)(l<<3); if ((n>>3)!=(unsigned short)l) break; if (n+(l<<1) < n) break; n=(unsigned short)(n+(l<<1)); if (n+c < n) break; n=(unsigned short)(n+c); #endif if (n > maxshort+neg) break; l=(short)n; ++tmp; ok=1; } if (!ok) return 0; *dest=(short)(neg?-l:l); return (size_t)(tmp-src); }