text: /* CC0 license (public domain) - see LICENSE file for details */
  #include <ccan/str/hex/hex.h>
  #include <assert.h>
  #include <stdio.h>
  #include <stdlib.h>
  
  static bool char_to_hex(unsigned char *val, char c)
  {
  	if (c >= '0' && c <= '9') {
  		*val = c - '0';
  		return true;
  	}
  	if (c >= 'a' && c <= 'f') {
  		*val = c - 'a' + 10;
  		return true;
  	}
  	if (c >= 'A' && c <= 'F') {
  		*val = c - 'A' + 10;
  		return true;
  	}
  	return false;
  }
  
  bool hex_decode(const char *str, size_t slen, void *buf, size_t bufsize)
  {
  	unsigned char v1, v2;
  	unsigned char *p = buf;
  
  	while (slen > 1) {
  		if (!char_to_hex(&v1, str[0]) || !char_to_hex(&v2, str[1]))
  			return false;
  		if (!bufsize)
  			return false;
  		*(p++) = (v1 << 4) | v2;
  		str += 2;
  		slen -= 2;
  		bufsize--;
  	}
  	return slen == 0 && bufsize == 0;
  }
  
  static char hexchar(unsigned int val)
  {
  	if (val < 10)
  		return '0' + val;
  	if (val < 16)
  		return 'a' + val - 10;
  	abort();
  }
  
  bool hex_encode(const void *buf, size_t bufsize, char *dest, size_t destsize)
  {
  	size_t i;
  
  	if (destsize < hex_str_size(bufsize))
  		return false;
  
  	for (i = 0; i < bufsize; i++) {
  		unsigned int c = ((const unsigned char *)buf)[i];
  		*(dest++) = hexchar(c >> 4);
  		*(dest++) = hexchar(c & 0xF);
  	}
  	*dest = '\0';
  
  	return true;
  }
  