#include <dir.h>
#include <stdio.h>
#include <string.h>

/*******************************************************************
// CATEGORY: File
// FUNCTION: CreateHexFile
// MODIFIED: 2025.9.28
// USAGE: int = CreateHexFile(*char FileName, *char HexString)
// BRIEF: Creates a binary file and writes some bytes into it
//
// This function creates a binary file and writes bytes into it.
// The function expects two string pointers, the first one pointing
// to a file name and the second one pointing to a string containing
// hexadecimal numbers. The function converts each hexadecimal
// digit pair into a byte and writes the bytes to a file.
// Non-hexadecimal digits in the arguments are ignored.
//
// If the file already exists, it will be deleted and replaced
// with the new content. The function returns 1 on success or
// zero if something went wrong.
//
// Note: Part of the original HexString will be overwritten with the
// binary content, so this function destroys the second argument.
//
// Usage: int = CreateHexFile(char *FileName, char *HexString)
*/
int CreateHexFile(char *FileName, char *HexString)
{
  /* This lookup table helps us convert hexadecimal digits to integers quickly */
  char *LUT = "ABCDEFGHIJ.......KLMNOPQ.........................KLMNOPQ";
  char c, hi, odd = 0;
  int i = 0, j = 0;
  FILE *f;

  if ((f = fopen(FileName, "wb")) == NULL)
  {
	fprintf(stderr, "Error: Cannot create file.\n");
	return 0;
  }

  while ((c = HexString[i++]) != 0)
  {
	if (c < 48 || c > 102)
	  continue;             /* Non-hex char */
	if ((c = LUT[c - 48]) < 65)
	  continue;             /* Non-hex char */
	c -= 65;

	/* hex digit is now converted to an integer */

	if ((odd = !odd) != 0)
	  hi = c << 4;
	else
	  HexString[j++] = hi | c;
  }

  /* Save last digit if there are odd number of hex digits */
  if (odd) HexString[j++] = hi;

  /* Write converted binary data to file */
  fwrite(HexString, j, 1, f);

  fclose(f);

  return 1;
}

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

void main()
{
  int i;
  char CharTable[513];
  char *ptr = CharTable;

  /* Create a list of hexadecimal numbers from 00 to FF */
  for (i = 0; i < 256; i++, ptr += 2)
	sprintf(ptr, "%.2X", i);
  CharTable[513] = 0;

  mkdir("C:\\TEMP");
  CreateHexFile("C:\\TEMP\\ASCII.BIN", CharTable);
}