hexconversion.c

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#include "hexconversion.h"
void bytetohex(unsigned char decimal, char hex[3]) {

  const char *hexdigits = "0123456789ABCDEF";
  int rest, number;
  hex[0] = '0';
  hex[1] = '0';
  hex[2] = '\0';

  number = decimal / 16;
  rest = decimal % 16;

  hex[0] = hexdigits[number];
  hex[1] = hexdigits[rest];
}

char tohex(char num) {
  if (num<10)
    return num+'0';
  else if (num<16)
    return num-10+'a';
  else
    return -1;
}

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