hex.c

#include <stdio.h>

char hex( char h )
{
	signed char xa = '0' - h;
	signed char xb = h - ('9' + 1);
	signed char ya = ('A' - 1) - h;
	signed char yb = h - ('F' + 1);
	signed char za = ('a' - 1) - h;
	signed char zb = h - ('f' + 1);
	return  -(xa  & (xa&xb)>>7
	     | (ya-9) & (ya&yb)>>7
	     | (za-9) & (za&zb)>>7);
}

int main()
{
	char s[]="_##$#$@0123456789abcdefABCDEF!@#!@#/ZXCzxc*&#$%";
//	char s[]="0123456789abcdefABCDEF";
	int i;
	for(i=0; i<sizeof(s)-1; i++)
		printf( "%1x ", hex(s[i]));
	printf("\n");
}