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25 lines
992 B
C
25 lines
992 B
C
#include "scan.h"
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size_t scan_8short(const char* src,unsigned short* dest) {
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/* make a copy of src so we can return the number of bytes we progressed */
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register const char *tmp=src;
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/* this is called l because we copy and pasted from 8long, where l
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* stood for "long" */
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register unsigned short l=0;
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register unsigned char c;
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/* *tmp - '0' can be negative, but casting to unsigned char makes
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* those cases positive and large; that means we only need one
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* comparison. This trick is no longer needed on modern compilers,
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* but we also want to produce good code on old compilers :) */
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while ((c=(unsigned char)(*tmp-'0'))<8) {
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/* overflow check; for each digit we multiply by 8 and then add the
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* digit; 0-7 needs 3 bits of storage, so we need to check if the
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* uppermost 3 bits of l are empty. Do it by shifting to the right */
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if (l>>(sizeof(l)*8-3)) break;
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l=(unsigned short)(l*8+c);
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++tmp;
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}
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*dest=l;
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return (size_t)(tmp-src);
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}
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