#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <fcntl.h>

int convert(unsigned char *infile, unsigned char *outfile)
{
    int inf, outf;
    unsigned char inpix[3];
    unsigned char outpix[2];
    unsigned int pix;
    unsigned char red, green, blue;
    
    printf("Opening input file %s: ", infile);
    inf = open(infile, O_RDONLY);
    if(inf < 1)
    {
        printf("ERROR: can't open input file\r\n");
        return -1;
    }
    printf("OK\r\n");
    
    printf("Opening output file %s: ", outfile);
    outf = open(outfile,  O_WRONLY|O_CREAT);
    if(outf < 1)
    {
        printf("ERROR: can't open output file\r\n");
        return -1;
    }
    printf("OK\r\n");
    
    while(read(inf, inpix, 3) == 3)
    {
        red = inpix[0] >> 3;
        green = inpix[1] >> 2;
        blue = inpix[2] >> 3;

        pix = red;
        pix <<= 6;
        pix |= green;
        pix <<= 5;
        pix |= blue;
        
        outpix[0] = (pix & 0x000000FF);
        outpix[1] = ((pix & 0x0000FF00) >> 8);
        
        write(outf, outpix, 2);
    }
    
    
    close(inf);
    close(outf);
    
    return 0;
}

int main(int argc, char **argv) 
{
    if (argc<3) 
    {
        printf("Usage: %s <infile> <outfile>\r\n",argv[0]);
        printf("<infile> is a raw RGB file, 8 bit per value, 24 bits per pixel.\r\n");
        printf("<outfile> is the resulting packed RGB file with 16 bits per pixel\r\n");
        exit(1);
    }

    return convert(argv[1], argv[2]);
}