rle_getskip.c

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/*
 * This software is copyrighted as noted below.  It may be freely copied,
 * modified, and redistributed, provided that the copyright notice is 
 * preserved on all copies.
 * 
 * There is no warranty or other guarantee of fitness for this software,
 * it is provided solely "as is".  Bug reports or fixes may be sent
 * to the author, who may or may not act on them as he desires.
 *
 * You may not include this software in a program or other software product
 * without supplying the source, or without informing the end-user that the 
 * source is available for no extra charge.
 *
 * If you modify this software, you should include a notice giving the
 * name of the person performing the modification, the date of modification,
 * and the reason for such modification.
 */
/* 
 * rle_getskip.c - Skip scanlines on input.
 * 
 * Author:  Spencer W. Thomas
 *      EECS Dept.
 *      University of Michigan
 * Date:    Wed Jun 27 1990
 * Copyright (c) 1990, University of Michigan
 */

#include "rle.h"
#include "rle_code.h"

/* Read a two-byte "short" that started in VAX (LITTLE_ENDIAN) order */
#define VAXSHORT( var, fp )
    { var = fgetc(fp)&0xFF; var |= (fgetc(fp)) << 8; }

/* Instruction format -- first byte is opcode, second is datum. */

#define OPCODE(inst) (inst[0] & ~LONG)
#define LONGP(inst) (inst[0] & LONG)
#define DATUM(inst) (inst[1] & 0xff)    /* Make sure it's unsigned. */

/*****************************************************************
 * TAG( rle_getskip )
 * 
 * Skip the next scanline with data on it.
 * Most useful for skipping to end-of-image.
 * Inputs:
 *  the_hdr:    Describes input image.
 * Outputs:
 *  Returns the number of the next scanline.  At EOF returns 32768.
 * Assumptions:
 *  rle_get_setup has been called.
 * Algorithm:
 *  Read input to the beginning of the next scanline, or to EOF or
 *  end of image.
 */
unsigned int
rle_getskip( the_hdr )
rle_hdr *the_hdr;
{
    unsigned char inst[2];
    register FILE *infile = the_hdr->rle_file;
    int nc;

    /* Add in vertical skip from last scanline */
    if ( the_hdr->priv.get.vert_skip > 0)
    the_hdr->priv.get.scan_y += the_hdr->priv.get.vert_skip;
    the_hdr->priv.get.vert_skip = 0;

    if ( the_hdr->priv.get.is_eof )
    return 32768;       /* too big for 16 bits, signal EOF */

    /* Otherwise, read and interpret instructions until a skipLines
     * instruction is encountered.
     */
    for (;;)
    {
        inst[0] = getc( infile );
    inst[1] = getc( infile );
    if ( feof(infile) )
    {
        the_hdr->priv.get.is_eof = 1;
        break;      /* <--- one of the exits */
    }

    switch( OPCODE(inst) )
    {
    case RSkipLinesOp:
        if ( LONGP(inst) )
        {
        VAXSHORT( the_hdr->priv.get.vert_skip, infile );
        }
        else
        the_hdr->priv.get.vert_skip = DATUM(inst);
        break;          /* need to break for() here, too */

    case RSetColorOp:
        /* No-op here. */
        break;

    case RSkipPixelsOp:
        if ( LONGP(inst) )
        {
        (void)getc( infile );
        (void)getc( infile );
        }
        break;

    case RByteDataOp:
        if ( LONGP(inst) )
        {
            VAXSHORT( nc, infile );
        }
        else
        nc = DATUM(inst);
        nc++;
        if ( the_hdr->priv.get.is_seek )
        fseek( infile, ((nc + 1) / 2) * 2, 1 );
        else
        {
        register int ii;
        for ( ii = ((nc + 1) / 2) * 2; ii > 0; ii-- )
            (void) getc( infile );  /* discard it */
        }

        break;

    case RRunDataOp:
        if ( LONGP(inst) )
        {
        (void)getc( infile );
        (void)getc( infile );
        }
        (void)getc( infile );
        (void)getc( infile );
        break;

    case REOFOp:
        the_hdr->priv.get.is_eof = 1;
        break;

    default:
        fprintf( stderr,
             "%s: rle_getskip: Unrecognized opcode: %d, reading %s\n",
             the_hdr->cmd, OPCODE(inst), the_hdr->file_name );
        exit(1);
    }
    if ( OPCODE(inst) == REOFOp )
        break;          /* <--- the other loop exit */
    if ( OPCODE(inst) == RSkipLinesOp )
        break;
    }

    /* Return the number of the NEXT scanline. */
    the_hdr->priv.get.scan_y +=
    the_hdr->priv.get.vert_skip;
    the_hdr->priv.get.vert_skip = 0;

    if ( the_hdr->priv.get.is_eof )
    return 32768;       /* too big for 16 bits, signal EOF */
    else
    return the_hdr->priv.get.scan_y;
}