gistfile1.cpp

#include <stdio.h>

#define IMAGE_WIDTH 7
#define DISPLAY_WIDTH 192
#define DISPLAY_HEIGHT 160

unsigned long int display[(DISPLAY_WIDTH * DISPLAY_HEIGHT) / 32];

int asciiHexToDec(char asciiHex)
{
   if ((asciiHex >= '0') && (asciiHex <= '9')) return (asciiHex - '0');
   if ((asciiHex >= 'A') && (asciiHex <= 'F')) return (10 + (asciiHex - 'A'));
   return -1; // error
}

int zeroLastBits(int c, int bits)
{
   return ((c >> bits) << bits);
}

int zeroLastBits2(int c, int bits)
{
   int mask = (1 << bits);
   mask = mask - 1;
   mask = ~mask;
   return (c & mask);
}

bool readFile()
{
   FILE* file = fopen("image.hex", "r");
   if (!file) return false;

   int c;
   unsigned long int result = 0;
   int offsetSource = 28; // offset within result
   int offsetDest   = 0;  // offset within display memory 
   int y            = 0;  // current line on display memory
   int pixelsOnLine = 0;  // total number of pixels written on the current line

   while ((c = fgetc(file)) != EOF) {
      c = asciiHexToDec(c);
      if (c < 0) { // error
         fclose(file);
         return false;
      }

      if (pixelsOnLine + 4 <= IMAGE_WIDTH) {
         result += (c << offsetSource);
         offsetSource -= 4;
         pixelsOnLine += 4;
         if (offsetSource < 0) {
            display[offsetDest] = result;
            offsetDest++;
            result = 0;
            offsetSource = 28;
         }
      } else {
         int pixelsNextLine = (pixelsOnLine + 4) - IMAGE_WIDTH;
         int pixelsRemaining = 4 - pixelsNextLine;
         int cCurrentLineValue = zeroLastBits2(c, pixelsNextLine);
         int cNextLineValue = c - cCurrentLineValue;

         // finish current line
         result += (cCurrentLineValue << offsetSource);
         display[offsetDest] = result;
         y++;
         offsetDest = y * (DISPLAY_WIDTH / 32);
         result = 0;
         offsetSource = 32 - pixelsNextLine;

         // start next line
         result += (cNextLineValue << offsetSource);
         offsetSource -= 4;
         pixelsOnLine = pixelsNextLine;
      }
   }

   // flush the remaining data
   display[offsetDest] = result;

   fclose(file);
   return true; // success
}

bool dumpDisplayMemory()
{
   FILE* file = fopen("display.dat", "wb");
   if (!file) return false;

   for (int i = 0; i < (DISPLAY_WIDTH * DISPLAY_HEIGHT) / 32; i++) {
      if (fwrite(&display[i], sizeof(display[0]), 1, file) != 1) { // error
         fclose(file);
         return false;
      }
   }

   fclose(file);
   return true; // success
}

int main(int argc, char* argv[])
{
   if (!readFile()) return -1; // error
   if (!dumpDisplayMemory()) return -1; // error

   return 0; // success
}

image.hex

A548