/* Function: FDV_PIXEL_FAST 
   Purpose:  Plot a pixel to the VGA Screen (320x200x256) 
   Parameters: x = Horizontal Screen Position ( Value: 0 < x < 320 )
               y = Vertical Screen Position   ( Value: 0 < y < 200 )
               cor = pixel color              (Value: 0 < cor < 256) 
                                    
   Compiler: Watcom C/C++ 11.0 (32bit Protected Mode - DOS4GW) 
   Author: Fabio D. Vecchia
   Extracted from Fabio Vecchia's Game Library (c) 1995 - (FDV_LB95)
*/

// Initializing the screen buffer 
unsigned char *buf_tela=(unsigned char *)0x0a0000;

void fdv_pixel_fast(long x, long y, unsigned char cor)
{
    buf_tela[(y<<8) + (y<<6) + x]=cor;
}

/* Comment: What does the expression [(y<<8) + (y<<6) + x] mean?
            It is similar to [y*320+x], but it is much faster, because
            shift (<< or >>) operations require less CPU usage than 
            multiplying operations.
   Comparing:    y<<8 = y*256
                 y<<6 = y*64
                 Then, (y<<8) + (y<<6) = (y*256) + (y*64) = y*320
                 So, (y<<8) + (y<<6) + x = y*320+x 
*/