Mirror of :pserver:cvs@cvs.fefe.de:/cvs libowfat https://www.fefe.de/libowfat/
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#include "scan.h"
static const unsigned int maxint = ((unsigned int)-1)>>1;
size_t scan_int(const char* src,int* dest) {
register const char *tmp;
register int l;
register unsigned char c;
unsigned int neg;
int ok;
tmp=src; l=0; ok=0; neg=0;
switch (*tmp) {
case '-': neg=1; /* fall through */
case '+': ++tmp;
}
while ((c=(unsigned char)(*tmp-'0'))<10) {
unsigned 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=(unsigned int)l<<3; if ((n>>3)!=(unsigned int)l) break;
if (n+((unsigned int)l<<1) < n) break;
n+=(unsigned int)l<<1;
if (n+c < n) break;
n+=c;
if (n > maxint+neg) break;
l=(int)n;
++tmp;
ok=1;
}
if (!ok) return 0;
*dest=(neg?-l:l);
return (size_t)(tmp-src);
}