/*
 * convert.c -- uncompressed GIF image data encoder
 *
 * Copyright (c) 1995-1997 by nir@mxa.meshnet.or.jp
 *
 * This file is part of npc.cgi source tree.
 * npc.cgi is free software; you can redistribute it and/or modify it
 * for any purpose.
 *
 * @(#)$Id: convert.c,v 1.4 1997/12/11 14:03:48 nir Rel $
 */

/*
 * $Log: convert.c,v $
 * Revision 1.4  1997/12/11 14:03:48  nir
 * To avoid infringement of the LZW Unisys patent, dispose compression
 * routine and use uncompressed data encoder.
 *
 * Revision 1.3  1997/11/05 11:45:38  nir
 * Add Copyright, Id and Log.
 *
 */

#include "npc.h"

#define BITS	12

#define MAXCODE(n_bits)	(1 << (n_bits))
#define MAXMAXCODE	MAXCODE(BITS)

INTERN void put_code(unsigned int w);
INTERN void write_code_buf(unsigned int bits_len);
INTERN void put_clear(void);

INTERN short clear, eoinf, first;

INTERN unsigned char buf[258];
INTERN unsigned char *code_buf_base;
INTERN unsigned char *code_buf;
INTERN unsigned int bit_offset;
INTERN unsigned int n_bits;
INTERN unsigned int min_n_bits;
INTERN short maxcode;
INTERN short next_w;

int convert(unsigned int min_code_size,
	unsigned char *pixel,
	unsigned int len) {

	if (len <= 0)
		return(BAD);

	code_buf_base = buf;
	code_buf = buf + 1;

	clear = 1 << min_code_size;
	eoinf = clear + 1;
	first = clear + 2;

	n_bits = min_n_bits = min_code_size + 1;

	bit_offset = 0;
	code_buf[0] = 0;

	put_clear();
	while (len-- > 0) {
		put_code(*(pixel++));
		if (next_w >= MAXMAXCODE) {
			put_clear();
		} else if (++next_w > maxcode) {
			maxcode = MAXCODE(++n_bits);
		}
	}
	put_code(eoinf);
	write_code_buf(bit_offset);
	gputc(0);	/* end of sub-block */
	return(0);
}


INTERN void put_code(unsigned int w) {
	unsigned int r_pos, r_off;

	r_pos = bit_offset / 8;
	r_off = bit_offset % 8;
	code_buf[r_pos] |= (unsigned char)(w << r_off);
	code_buf[r_pos + 1] = (unsigned char)(w >> (8 - r_off));
	code_buf[r_pos + 2] = (unsigned char)0;
	bit_offset += n_bits;
	if (bit_offset < 255 * 8)
		return;
	write_code_buf(255 * 8);
	code_buf[0] = code_buf[255];
	code_buf[1] = code_buf[256];
	bit_offset -= 255 * 8;
}


INTERN void write_code_buf(unsigned int bits_len) {
	unsigned int len;

	if ((len = (bits_len + 7) / 8) == 0)
		return;
	*code_buf_base = (unsigned char)len;
	gwrite(code_buf_base, len + 1);
}


INTERN void put_clear(void) {
	put_code(clear);
	maxcode = MAXCODE(n_bits = min_n_bits);
	next_w = first;
}