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38 lines
1.2 KiB
C
38 lines
1.2 KiB
C
#include "scan.h"
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size_t scan_8int(const char* src,unsigned int* 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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register unsigned int 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=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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#ifdef UNITTEST
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#include <assert.h>
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int main() {
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unsigned int i;
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assert(scan_8int("1234",&i)==4 && i==01234);
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assert(scan_8int("12345678",&i)==7 && i==01234567);
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assert(scan_8int("37777777777",&i)==11 && i==0xffffffff);
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assert(scan_8int("40000000000",&i)==10 && i==04000000000);
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assert(scan_8int("-4",&i)==0 && i==0);
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assert(scan_8int("01234",&i)==5 && i==01234);
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return 0;
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}
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#endif
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