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26 lines
794 B
C
26 lines
794 B
C
#include "scan.h"
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size_t scan_ulongn(const char* src,size_t n,unsigned long int* dest) {
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register const char *tmp=src;
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register unsigned long int l=0;
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register unsigned char c;
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while (n-->0 && (c=(unsigned char)(*tmp-'0'))<10) {
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unsigned long int n;
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/* we want to do: l=l*10+c
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* but we need to check for integer overflow.
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* to check whether l*10 overflows, we could do
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* if ((l*10)/10 != l)
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* however, multiplication and division are expensive.
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* so instead of *10 we do (l<<3) (i.e. *8) + (l<<1) (i.e. *2)
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* and check for overflow on all the intermediate steps */
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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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++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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