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#include "byte.h"
/* str_diff returns negative, 0, or positive, depending on whether the
* string a[0], a[1], ..., a[n]=='\0' is lexicographically smaller than,
* equal to, or greater than the string b[0], b[1], ..., b[m-1]=='\0'.
* When the strings are different, str_diff does not read bytes past the
* first difference. */
int str_diffn(const char* a, const char* b, size_t limit) {
register const unsigned char* s=(const unsigned char*)a;
register const unsigned char* t=(const unsigned char*)b;
register const unsigned char* u=t+limit;
register int j;
j=0;
for (;;) {
if (t>=u || (j=(*s-*t)) || !*t) break;
++s; ++t;
if (t>=u || (j=(*s-*t)) || !*t) break;
++s; ++t;
if (t>=u || (j=(*s-*t)) || !*t) break;
++s; ++t;
if (t>=u || (j=(*s-*t)) || !*t) break;
++s; ++t;
}
return j;
}
#ifdef UNITTEST
#include <assert.h>
#include <string.h>
int main() {
assert(str_diffn("foo","foo",3)==0);
assert(str_diffn("foo","fob",3)==('o'-'b'));
assert(str_diffn("foo","foox",4)==(-'x'));
assert(str_diffn("foox","foo",4)=='x');
assert(str_diffn("foo","fob",2)==0);
}
#endif
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