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/* Copyright (C) 2015 Luke Shumaker <lukeshu@lukeshu.com> */
#include <stdio.h>
/* ungetc is only guaranteed for 1 char; use our own buffer */
int buf[2];
int cnt = 0;
int ab = 0;
int _getchar() {
if (cnt > 0)
cnt--;
else
buf[ab] = getchar();
int ret = buf[ab];
ab = !ab;
return ret;
}
void _ungetchar() {
cnt++;
ab = !ab;
}
int hex(int c) {
if ('0' <= c && c <= '9')
return c - '0';
if ('A' <= c && c <= 'F')
return 10 + c - 'A';
if ('a' <= c && c <= 'f')
return 10 + c - 'a';
return -1;
}
int
main () {
int c, v1, v2;
while ((c = _getchar()) != EOF) {
switch (c) {
case '%':
if ((v1 = hex(_getchar())) < 0) {
putchar('%');
_ungetchar();
continue;
}
if ((v2 = hex(_getchar())) < 0) {
putchar('%');
_ungetchar();
_ungetchar();
continue;
}
putchar(((v1 << 4) & 0xF0) | (v2 & 0x0F));
break;
case '+':
putchar(' ');
break;
default:
putchar(c);
break;
}
}
return 0;
}
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