1  ///////////////////////////////////////////////////////////////////////////////
       2  //
       3  /// \file       hex2bin.c
       4  /// \brief      Converts hexadecimal input strings to binary
       5  //
       6  //  Author:     Lasse Collin
       7  //
       8  //  This file has been put into the public domain.
       9  //  You can do whatever you want with this file.
      10  //
      11  ///////////////////////////////////////////////////////////////////////////////
      12  
      13  #include "sysdefs.h"
      14  #include <stdio.h>
      15  #include <ctype.h>
      16  
      17  
      18  static int
      19  getbin(int x)
      20  {
      21  	if (x >= '0' && x <= '9')
      22  		return x - '0';
      23  
      24  	if (x >= 'A' && x <= 'F')
      25  		return x - 'A' + 10;
      26  
      27  	return x - 'a' + 10;
      28  }
      29  
      30  
      31  int
      32  main(void)
      33  {
      34  	while (true) {
      35  		int byte = getchar();
      36  		if (byte == EOF)
      37  			return 0;
      38  		if (!isxdigit(byte))
      39  			continue;
      40  
      41  		const int digit = getchar();
      42  		if (digit == EOF || !isxdigit(digit)) {
      43  			fprintf(stderr, "Invalid input\n");
      44  			return 1;
      45  		}
      46  
      47  		byte = (getbin(byte) << 4) | getbin(digit);
      48  		if (putchar(byte) == EOF) {
      49  			perror(NULL);
      50  			return 1;
      51  		}
      52  	}
      53  }