sbc.c

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/*
 * Bluetooth low-complexity, subband codec (SBC)
 *
 * Copyright (C) 2017  Aurelien Jacobs <aurel@gnuage.org>
 * Copyright (C) 2012-2013  Intel Corporation
 * Copyright (C) 2008-2010  Nokia Corporation
 * Copyright (C) 2004-2010  Marcel Holtmann <marcel@holtmann.org>
 * Copyright (C) 2004-2005  Henryk Ploetz <henryk@ploetzli.ch>
 * Copyright (C) 2005-2008  Brad Midgley <bmidgley@xmission.com>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * SBC common functions for the encoder and decoder
 */

#include "avcodec.h"
#include "sbc.h"

/* A2DP specification: Appendix B, page 69 */
static const int sbc_offset4[4][4] = {
    { -1, 0, 0, 0 },
    { -2, 0, 0, 1 },
    { -2, 0, 0, 1 },
    { -2, 0, 0, 1 }
};

/* A2DP specification: Appendix B, page 69 */
static const int sbc_offset8[4][8] = {
    { -2, 0, 0, 0, 0, 0, 0, 1 },
    { -3, 0, 0, 0, 0, 0, 1, 2 },
    { -4, 0, 0, 0, 0, 0, 1, 2 },
    { -4, 0, 0, 0, 0, 0, 1, 2 }
};

/*
 * Calculates the CRC-8 of the first len bits in data
 */
uint8_t ff_sbc_crc8(const AVCRC *ctx, const uint8_t *data, size_t len)
{
    size_t byte_length = len >> 3;
    int bit_length = len & 7;
    uint8_t crc;

    crc = av_crc(ctx, 0x0F, data, byte_length);

    if (bit_length) {
        uint8_t bits = data[byte_length];
        while (bit_length--) {
            int8_t mask = bits ^ crc;
            crc = (crc << 1) ^ ((mask >> 7) & 0x1D);
            bits <<= 1;
        }
    }

    return crc;
}

/*
 * Code straight from the spec to calculate the bits array
 * Takes a pointer to the frame in question and a pointer to the bits array
 */
void ff_sbc_calculate_bits(const struct sbc_frame *frame, int (*bits)[8])
{
    int subbands = frame->subbands;
    uint8_t sf = frame->frequency;

    if (frame->mode == MONO || frame->mode == DUAL_CHANNEL) {
        int bitneed[2][8], loudness, max_bitneed, bitcount, slicecount, bitslice;
        int ch, sb;

        for (ch = 0; ch < frame->channels; ch++) {
            max_bitneed = 0;
            if (frame->allocation == SNR) {
                for (sb = 0; sb < subbands; sb++) {
                    bitneed[ch][sb] = frame->scale_factor[ch][sb];
                    if (bitneed[ch][sb] > max_bitneed)
                        max_bitneed = bitneed[ch][sb];
                }
            } else {
                for (sb = 0; sb < subbands; sb++) {
                    if (frame->scale_factor[ch][sb] == 0)
                        bitneed[ch][sb] = -5;
                    else {
                        if (subbands == 4)
                            loudness = frame->scale_factor[ch][sb] - sbc_offset4[sf][sb];
                        else
                            loudness = frame->scale_factor[ch][sb] - sbc_offset8[sf][sb];
                        if (loudness > 0)
                            bitneed[ch][sb] = loudness / 2;
                        else
                            bitneed[ch][sb] = loudness;
                    }
                    if (bitneed[ch][sb] > max_bitneed)
                        max_bitneed = bitneed[ch][sb];
                }
            }

            bitcount = 0;
            slicecount = 0;
            bitslice = max_bitneed + 1;
            do {
                bitslice--;
                bitcount += slicecount;
                slicecount = 0;
                for (sb = 0; sb < subbands; sb++) {
                    if ((bitneed[ch][sb] > bitslice + 1) && (bitneed[ch][sb] < bitslice + 16))
                        slicecount++;
                    else if (bitneed[ch][sb] == bitslice + 1)
                        slicecount += 2;
                }
            } while (bitcount + slicecount < frame->bitpool);

            if (bitcount + slicecount == frame->bitpool) {
                bitcount += slicecount;
                bitslice--;
            }

            for (sb = 0; sb < subbands; sb++) {
                if (bitneed[ch][sb] < bitslice + 2)
                    bits[ch][sb] = 0;
                else {
                    bits[ch][sb] = bitneed[ch][sb] - bitslice;
                    if (bits[ch][sb] > 16)
                        bits[ch][sb] = 16;
                }
            }

            for (sb = 0; bitcount < frame->bitpool &&
                            sb < subbands; sb++) {
                if ((bits[ch][sb] >= 2) && (bits[ch][sb] < 16)) {
                    bits[ch][sb]++;
                    bitcount++;
                } else if ((bitneed[ch][sb] == bitslice + 1) && (frame->bitpool > bitcount + 1)) {
                    bits[ch][sb] = 2;
                    bitcount += 2;
                }
            }

            for (sb = 0; bitcount < frame->bitpool &&
                            sb < subbands; sb++) {
                if (bits[ch][sb] < 16) {
                    bits[ch][sb]++;
                    bitcount++;
                }
            }

        }

    } else if (frame->mode == STEREO || frame->mode == JOINT_STEREO) {
        int bitneed[2][8], loudness, max_bitneed, bitcount, slicecount, bitslice;
        int ch, sb;

        max_bitneed = 0;
        if (frame->allocation == SNR) {
            for (ch = 0; ch < 2; ch++) {
                for (sb = 0; sb < subbands; sb++) {
                    bitneed[ch][sb] = frame->scale_factor[ch][sb];
                    if (bitneed[ch][sb] > max_bitneed)
                        max_bitneed = bitneed[ch][sb];
                }
            }
        } else {
            for (ch = 0; ch < 2; ch++) {
                for (sb = 0; sb < subbands; sb++) {
                    if (frame->scale_factor[ch][sb] == 0)
                        bitneed[ch][sb] = -5;
                    else {
                        if (subbands == 4)
                            loudness = frame->scale_factor[ch][sb] - sbc_offset4[sf][sb];
                        else
                            loudness = frame->scale_factor[ch][sb] - sbc_offset8[sf][sb];
                        if (loudness > 0)
                            bitneed[ch][sb] = loudness / 2;
                        else
                            bitneed[ch][sb] = loudness;
                    }
                    if (bitneed[ch][sb] > max_bitneed)
                        max_bitneed = bitneed[ch][sb];
                }
            }
        }

        bitcount = 0;
        slicecount = 0;
        bitslice = max_bitneed + 1;
        do {
            bitslice--;
            bitcount += slicecount;
            slicecount = 0;
            for (ch = 0; ch < 2; ch++) {
                for (sb = 0; sb < subbands; sb++) {
                    if ((bitneed[ch][sb] > bitslice + 1) && (bitneed[ch][sb] < bitslice + 16))
                        slicecount++;
                    else if (bitneed[ch][sb] == bitslice + 1)
                        slicecount += 2;
                }
            }
        } while (bitcount + slicecount < frame->bitpool);

        if (bitcount + slicecount == frame->bitpool) {
            bitcount += slicecount;
            bitslice--;
        }

        for (ch = 0; ch < 2; ch++) {
            for (sb = 0; sb < subbands; sb++) {
                if (bitneed[ch][sb] < bitslice + 2) {
                    bits[ch][sb] = 0;
                } else {
                    bits[ch][sb] = bitneed[ch][sb] - bitslice;
                    if (bits[ch][sb] > 16)
                        bits[ch][sb] = 16;
                }
            }
        }

        ch = 0;
        sb = 0;
        while (bitcount < frame->bitpool) {
            if ((bits[ch][sb] >= 2) && (bits[ch][sb] < 16)) {
                bits[ch][sb]++;
                bitcount++;
            } else if ((bitneed[ch][sb] == bitslice + 1) && (frame->bitpool > bitcount + 1)) {
                bits[ch][sb] = 2;
                bitcount += 2;
            }
            if (ch == 1) {
                ch = 0;
                sb++;
                if (sb >= subbands)
                    break;
            } else
                ch = 1;
        }

        ch = 0;
        sb = 0;
        while (bitcount < frame->bitpool) {
            if (bits[ch][sb] < 16) {
                bits[ch][sb]++;
                bitcount++;
            }
            if (ch == 1) {
                ch = 0;
                sb++;
                if (sb >= subbands)
                    break;
            } else
                ch = 1;
        }

    }

}