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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;
#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 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;
#endif
if (n > maxint+neg) break;
l=(int)n;
++tmp;
ok=1;
}
if (!ok) return 0;
*dest=(neg?(int)-(unsigned int)l:l);
return (size_t)(tmp-src);
}
#ifdef UNITTEST
#include <assert.h>
int main() {
int i;
assert(scan_int("1234",&i)==4 && i==1234);
assert(scan_int("-1234",&i)==5 && i==-1234);
assert(scan_int("+1234",&i)==5 && i==1234);
assert(scan_int("4294967295",&i)==9 && i==429496729); // overflow
assert(scan_int("2147483647",&i)==10 && i==2147483647); // MAX_INT
assert(scan_int("2147483648",&i)==9 && i==214748364); // overflow
assert(scan_int("-2147483648",&i)==11 && i==-2147483648); // MIN_INT
assert(scan_int("-2147483649",&i)==10 && i==-214748364); // underflow
return 0;
}
#endif
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