Mirror of :pserver:cvs@cvs.fefe.de:/cvs libowfat https://www.fefe.de/libowfat/
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#include "scan.h"
size_t scan_8short(const char* src,unsigned short* dest) {
/* make a copy of src so we can return the number of bytes we progressed */
register const char *tmp=src;
/* this is called l because we copy and pasted from 8long, where l
* stood for "long" */
register unsigned short l=0;
register unsigned char c;
/* *tmp - '0' can be negative, but casting to unsigned char makes
* those cases positive and large; that means we only need one
* comparison. This trick is no longer needed on modern compilers,
* but we also want to produce good code on old compilers :) */
while ((c=(unsigned char)(*tmp-'0'))<8) {
/* overflow check; for each digit we multiply by 8 and then add the
* digit; 0-7 needs 3 bits of storage, so we need to check if the
* uppermost 3 bits of l are empty. Do it by shifting to the right */
if (l>>(sizeof(l)*8-3)) break;
l=(unsigned short)(l*8+c);
return (size_t)(tmp-src);
#include <assert.h>
int main() {
unsigned short i;
assert(scan_8short("1234",&i)==4 && i==01234);
assert(scan_8short("5678",&i)==3 && i==0567);
assert(scan_8short("177777",&i)==6 && i==0xffff);
assert(scan_8short("200000",&i)==5 && i==020000);
assert(scan_8short("-4",&i)==0 && i==0);
assert(scan_8short("01234",&i)==5 && i==01234);
return 0;