/*
 * The Python Imaging Library.
 * $Id$
 *
 * decoder for PackBits image data.
 *
 * history:
 *	96-04-19 fl	Created
 *
 * Copyright (c) Fredrik Lundh 1996.
 * Copyright (c) Secret Labs AB 1997.
 *
 * See the README file for information on usage and redistribution.
 */


#include "Imaging.h"

int
ImagingPackbitsDecode(Imaging im, ImagingCodecState state,
		      UINT8* buf, int bytes)
{
    UINT8 n;
    UINT8* ptr;
    int i;

    ptr = buf;

    for (;;) {

	if (bytes < 1)
	    return ptr - buf;

	if (ptr[0] & 0x80) {

	    if (ptr[0] == 0x80) {
		/* Nop */
		ptr++; bytes--;
		continue;
	    }

	    /* Run */
	    if (bytes < 2)
		return ptr - buf;

	    for (n = 257 - ptr[0]; n > 0; n--) {
		if (state->x >= state->bytes) {
		    /* state->errcode = IMAGING_CODEC_OVERRUN; */
		    break;
		}
		state->buffer[state->x++] = ptr[1];
	    }

	    ptr += 2; bytes -= 2;

	} else {

	    /* Literal */
	    n = ptr[0]+2;

	    if (bytes < n)
		return ptr - buf;

	    for (i = 1; i < n; i++) {
		if (state->x >= state->bytes) {
		    /* state->errcode = IMAGING_CODEC_OVERRUN; */
		    break;
		}
		state->buffer[state->x++] = ptr[i];
	    }

	    ptr += n; bytes -= n;

	}

	if (state->x >= state->bytes) {

	    /* Got a full line, unpack it */
	    state->shuffle((UINT8*) im->image[state->y + state->yoff] +
			   state->xoff * im->pixelsize, state->buffer,
			   state->xsize);

	    state->x = 0;

	    if (++state->y >= state->ysize) {
		/* End of file (errcode = 0) */
		return -1;
	    }
	}

    }
}