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#include "scan.h"
#include "haveuint128.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;
/* Since the conditions can be computed at compile time, the compiler
* should only emit code for one of the implementations, depending on
* which architecture the code is compiled for. */
#if defined(__GNUC__) && (__GNUC__ >= 5)
/* implementation for recent gcc or clang */
int ok=0;
for (; n-->0 && (c=(unsigned char)(*tmp-'0'))<10; ++tmp) {
unsigned long v;
if (__builtin_mul_overflow(l,10,&v) || __builtin_add_overflow(v,c,&v))
break;
l=v;
ok=1;
}
if (!ok) return 0;
*dest=l;
return (size_t)(tmp-src);
#else
#ifdef HAVE_UINT128
if (sizeof(unsigned long)==sizeof(unsigned long long) && sizeof(unsigned long)<sizeof(__uint128_t)) {
/* implementation for 64-bit platforms with gcc */
for (; n-->0 && (c=(unsigned char)(*tmp-'0'))<10; ++tmp) {
__uint128_t L=(__uint128_t)l*10+c;
if ((L >> ((sizeof(L)-sizeof(l))*8))) break;
l=(unsigned long)L;
}
*dest=l;
return (size_t)(tmp-src);
} else
#endif
if (sizeof(unsigned long)<sizeof(unsigned long long)) {
/* implementation for 32-bit platforms */
for (; n-->0 && (c=(unsigned char)(*tmp-'0'))<10; ++tmp) {
unsigned long long L=(unsigned long long)l*10+c;
if ((unsigned long)L != L) break;
l=(unsigned long)L;
}
*dest=l;
return (size_t)(tmp-src);
} else {
/* implementation for 64-bit platforms without gcc */
while (n-->0 && (c=(unsigned char)(*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)+c < n) break;
l=n+(l<<1)+c;
++tmp;
}
if (tmp-src) *dest=l;
return (size_t)(tmp-src);
}
#endif
}
#ifdef UNITTEST
#include <assert.h>
int main() {
unsigned long l;
assert(scan_ulongn("4294967295",10,&l) == 10 && l==4294967295ul);
if (sizeof(unsigned long)==4) {
assert(scan_ulongn("4294967296",10,&l) == 9 && l==429496729);
} else {
assert(scan_ulongn("18446744073709551615",20,&l) == 20 && l==18446744073709551615ull);
assert(scan_ulongn("18446744073709551616",20,&l) == 19 && l==1844674407370955161ull);
}
assert(scan_ulongn("1234",3,&l)==3 && l==123);
return 0;
}
#endif