Base24 encode and decode

b24.c

/* 
Author: wangye
http://wangye.org/
 */
static const char sel[] = {
	'B','C','D','F','G',
	'H','J','K','M','P',
	'Q','R','T','V','W',
	'X','Y','2','3','4',
	'6','7','8','9', '\0'};
 
char *b24e(char *buf, unsigned char *byst, size_t sizeOfBytes)
{
	int i = 0;
	unsigned char *p = byst;
	while ((size_t)(i = (p-byst)) < sizeOfBytes) {
		buf[2*i] = sel[((*p) >> 4)];
		buf[(2*i)+1] = sel[23 - ((*p) & 0x0f)];
		p++;
	}
	buf[(2*i)+1] = '\0';
	return buf;
}
 
unsigned char *b24d(unsigned char *buf, char *str, size_t countOfChars)
{
	size_t i;
	char *p = str;
	char *loc[2];
	unsigned char n[2];
	if (countOfChars % 2)
		return NULL;
	for (i = 0; i < (countOfChars>>1); i++) {
 
		loc[0] = strchr( sel, str[2*i] );
		loc[1] = strchr( sel, str[ ( 2*i ) + 1 ] );
		if (loc[0] == NULL || loc[1] == NULL)
			return NULL;
		n[0] = (unsigned char)( loc[0] - sel );
		n[1] = 23 - (unsigned char)( loc[1] - sel );
		buf[i] = (unsigned char)((n[0] << 4) | n[1]);
	}
	return buf;
}