/* common.c - Don Yang (uguu.org)

   09/12/01
                                                                           */

#include<assert.h>
#include<stdio.h>
#include"common.h"

/* Ring buffer */
BYTE RingBuffer[BUFFER_SIZE];
int ProcOffset;               /* Current processing position */
int HistoryOffset;            /* Start of buffered output */
int InputOffset;              /* End of buffered input */

int FileSize;                 /* Input file size */
int iChecksum, oChecksum;     /* Automatic checksum */

/***************************************************************** GetByte */
DWORD GetByte(int absoffset, FILE *infile)
{
   int byte;

   if( absoffset < ProcOffset )
   {
      assert(ProcOffset - absoffset < HALF_BUFFER_SIZE);
      return (DWORD)RingBuffer[absoffset & BUFFER_MASK];
   }

   assert(absoffset - ProcOffset < HALF_BUFFER_SIZE);
   if( absoffset >= FileSize )
      return INPUT_EOF;
   while( absoffset >= InputOffset )
   {
      if( (byte = fgetc(infile)) == EOF )
      {
         FileSize = InputOffset++;
         break;
      }
      RingBuffer[(InputOffset++) & BUFFER_MASK] = (BYTE)byte;
      iChecksum ^= byte;
   }
   if( absoffset >= FileSize )
      return INPUT_EOF;

   return (DWORD)RingBuffer[absoffset & BUFFER_MASK];

} /* GetByte() */

/***************************************************************** PutByte */
void PutByte(BYTE data, FILE *outfile)
{
   (void)fputc((int)data, outfile);
   oChecksum ^= (int)data;

} /* PutByte() */

/***************************************************************** PutWord */
void PutWord(WORD data, FILE *outfile)
{
   (void)fputc((int)(data & 0xff), outfile);
   (void)fputc((int)(data >> 8), outfile);

} /* PutWord() */