1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
#include "scan.h"
static const unsigned long maxlong = ((unsigned long)-1)>>1;
size_t scan_longn(const char *src,size_t len,long *dest) {
register const char *tmp;
register long int l;
register unsigned char c;
unsigned int neg;
int ok;
if (!len) return 0;
tmp=src; l=0; ok=0; neg=0;
switch (*tmp) {
case '-': neg=1; /* fall through */
case '+': ++tmp; --len;
}
while (len-->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?(signed long int)-(unsigned long int)l:l);
return (size_t)(tmp-src);
}
|
