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40 lines
1.0 KiB
C
40 lines
1.0 KiB
C
#include "scan.h"
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size_t scan_ulonglong(const char *src,unsigned long long *dest) {
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register const char *tmp=src;
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register unsigned long long l=0;
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register unsigned char c;
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while ((c=(unsigned char)(*tmp-'0'))<10) {
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unsigned long long n;
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#if defined(__GNUC__) && (__GNUC__ >= 5)
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if (__builtin_mul_overflow(l,10,&n) || __builtin_add_overflow(n,c,&n))
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break;
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l=n;
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#else
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/* division is very slow on most architectures */
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n=l<<3; if ((n>>3)!=l) break;
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if (n+(l<<1) < n) break;
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n+=l<<1;
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if (n+c < n) break;
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l=n+c;
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#endif
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++tmp;
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}
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if (tmp-src) *dest=l;
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return (size_t)(tmp-src);
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}
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#ifdef UNITTEST
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#include <assert.h>
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int main() {
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unsigned long long l;
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assert(scan_ulonglong("0",&l)==1 && l==0);
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assert(scan_ulonglong("1",&l)==1 && l==1);
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assert(scan_ulonglong("4294967295",&l) == 10 && l==4294967295ull);
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assert(scan_ulonglong("18446744073709551615",&l) == 20 && l==18446744073709551615ull);
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assert(scan_ulonglong("18446744073709551616",&l) == 19 && l==1844674407370955161ull);
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return 0;
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}
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#endif
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