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85 lines
2.5 KiB
85 lines
2.5 KiB
/* Copyright (C) 2005 Ole André Vadla Ravnås <oleavr@gmail.com>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <stdlib.h>
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#include "mimic-private.h"
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extern guchar _col_zag[64];
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extern VlcSymbol _vlc_alphabet[16][128];
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/*
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* _vlc_encode_block
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*
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* Serialize an 8x8 block using variable length coding.
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*/
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void _vlc_encode_block(MimCtx *ctx, const gint *block, gint num_coeffs)
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{
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gint i, num_zeroes;
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/* The DC value is written out as is. */
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_write_bits(ctx, block[0], 8);
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/* Number of zeroes prefixing the next non-zero value. */
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num_zeroes = 0;
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for (i = 1; i < num_coeffs && num_zeroes <= 14; i++) {
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/* Fetch AC coefficients from block in zig-zag order. */
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gint value = block[_col_zag[i]];
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if (value != 0) {
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VlcSymbol sym;
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/* Clip input values to [-128, +128]. */
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if (value < -128)
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value = -128;
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else if (value > 128)
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value = 128;
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/* Look up symbol for the current non-zero value. */
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sym = _vlc_alphabet[num_zeroes][abs(value) - 1];
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/* No symbol? very rare... */
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if (sym.length1 <= 0)
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break;
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/* The symbols for negative values are the same as for positives, minus one. */
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if (value < 0) {
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if (sym.length2 > 0)
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sym.part2 -= 1;
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else
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sym.part1 -= 1;
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}
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/* Write out the full symbol. */
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_write_bits(ctx, sym.part1, sym.length1);
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if (sym.length2 > 0)
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_write_bits(ctx, sym.part2, sym.length2);
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/* Start counting zeroes again. */
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num_zeroes = 0;
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} else {
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num_zeroes++;
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}
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}
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/* Write out EOB if necessary. */
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if (num_zeroes > 0)
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_write_bits(ctx, 0xA, 4);
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}
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