Problem - Kevin Tafuro

leading “0x” if it exists. The exception is when there is whitespace. This function
passes back the number of bytes written in its second parameter. If that parameter is
negative, an error occurred.
Discussion
The spc_hex2bin( ) function shown in this section converts an ASCII string into a
binary string. Spaces and tabs are ignored. A leading “0x” or “0X” is ignored. There
are two cases in which this function can fail. First, if it sees a non-hexadecimal digit,
it assumes that the string is not in the right format, and it returns NULL, setting the
error parameter to ERR_NOT_HEX. Second, if there is an odd number of hex digits in the
string, it returns NULL, setting the error parameter to ERR_BAD_SIZE.
#include
#include
#include
#define ERR_NOT_HEX -1
#define ERR_BAD_SIZE -2
#define ERR_NO_MEM -3
unsigned char *spc_hex2bin(const unsigned char *input, size_t *l) {
unsigned char shift = 4, value = 0;
unsigned char *r, *ret;
const unsigned char *p;
if (!(r = ret = (unsigned char *)malloc(strlen(input) / 2))) {
*l = ERR_NO_MEM;
return 0;
}
for (p = input; isspace(*p); p++);
if (p[0] = = '0' && (p[1] = = 'x' || p[1] = = 'X')) p += 2;
while (p[0]) {
switch (p[0]) {
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
value |= (*p++ - '0')