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  1. #include "scan.h"
  2. size_t scan_8longlong(const char *src,unsigned long long *dest) {
  3. /* make a copy of src so we can return the number of bytes we progressed */
  4. register const char *tmp=src;
  5. register unsigned long long l=0;
  6. register unsigned char c;
  7. /* *tmp - '0' can be negative, but casting to unsigned char makes
  8. * those cases positive and large; that means we only need one
  9. * comparison. This trick is no longer needed on modern compilers,
  10. * but we also want to produce good code on old compilers :) */
  11. while ((c=(unsigned char)(*tmp-'0'))<8) {
  12. /* overflow check; for each digit we multiply by 8 and then add the
  13. * digit; 0-7 needs 3 bits of storage, so we need to check if the
  14. * uppermost 3 bits of l are empty. Do it by shifting to the right */
  15. if (l>>(sizeof(l)*8-3)) break;
  16. l=l*8+c;
  17. ++tmp;
  18. }
  19. *dest=l;
  20. return (size_t)(tmp-src);
  21. }
  22. #ifdef UNITTEST
  23. #include <assert.h>
  24. int main() {
  25. unsigned long long i;
  26. assert(scan_8longlong("1234",&i)==4 && i==01234);
  27. assert(scan_8longlong("12345678",&i)==7 && i==01234567);
  28. assert(scan_8longlong("1777777777777777777777",&i)==22 && i==0xffffffffffffffffull);
  29. assert(scan_8longlong("2000000000000000000000",&i)==21 && i==200000000000000000000ull);
  30. assert(scan_8longlong("-4",&i)==0 && i==0);
  31. assert(scan_8longlong("01234",&i)==5 && i==01234);
  32. return 0;
  33. }
  34. #endif