Programming

#include <stdio.h>
#include <string.h>
#include <stdlib.h>


int hexstr2bin(const char *hex_input, char *buf_output, size_t len);
static int hex2byte(const char *hex);
static int hex2num(char c);

main()
{
	int len;
	char* buf;

	const char* hex ="abcd1234567890";

	buf = (char*)malloc(100);

	len = strlen(hex);

	hexstr2bin(hex,buf,len);

	printf("Values in hex %s",buf);
}


int hexstr2bin(const char *hex_input, char *buf_output, size_t len)
{
	size_t i;
	int a;
	const char *ipos = hex;
	char *opos = buf;
	char *prefix = "0x";

	for (i = 0; i < len; i++) {
		a = hex2byte(ipos);
		if (a < 0)
			return -1;
		*opos++ = prefix[0];
		*opos++ = prefix[1];

			
		*opos++ = a;

		
		*opos++ = ',';
		ipos += 2;
	}
	return 0;
}


static int hex2byte(const char *hex)
{
	int a, b;
	a = hex2num(*hex++);
	if (a < 0)
		return -1;
	b = hex2num(*hex++);
	if (b < 0)
		return -1;
	return (a << 4) | b;
}


static int hex2num(char c)
{
	if (c >= '0' && c <= '9')
		return c - '0';
	if (c >= 'a' && c <= 'f')
		return c - 'a' + 10;
	if (c >= 'A' && c <= 'F')
		return c - 'A' + 10;
	return -1;
}