Convert two ASCII Hexadecimal Characters (Two ASCII bytes) in one byte

Question

I want to convert two ASCII bytes to one hexadecimal byte. eg.

0x30 0x43 => 0x0C , 0x34 0x46 => 0x4F ...

The ASCII bytes are a number bet

Answer 1

Here's a version that works with both upper and lower-case hex strings:

void hex_decode(const char *in, size_t len, uint8_t *out)
{
  unsigned int i, hn, ln;
  char hc, lc;

  memset(out, 0, len);

  for (i = 0; i < 2*len; i += 2) {

    hc = in[i];
    if ('a' <= hc && hc <= 'f') hc = toupper(hc);
    lc = in[i+1];
    if ('a' <= lc && lc <= 'f') lc = toupper(lc);

    hn = hc > '9' ? hc - 'A' + 10 : hc - '0';
    ln = lc > '9' ? lc - 'A' + 10 : lc - '0';

    out[i >> 1] = (hn << 4 ) | ln;
  }
}