26 lines
767 B

#include "scan.h"
size_t scan_ulongn(const char* src,size_t n,unsigned long int* dest) {
register const char *tmp=src;
register unsigned long int l=0;
register unsigned char c;
while (n-->0 && (c=*tmp-'0')<10) {
unsigned long int n;
/* 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=l<<3; if ((n>>3)!=l) break;
if (n+(l<<1) < n) break;
if (n+c < n) break;
if (tmp-src) *dest=l;
return tmp-src;