380 lines
11 KiB
C
380 lines
11 KiB
C
/******************************************************************************
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*
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* Copyright 2014 The Android Open Source Project
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* Copyright 2003 - 2004 Open Interface North America, Inc. All rights
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* reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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******************************************************************************/
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/*******************************************************************************
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$Revision: #1 $
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******************************************************************************/
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/**
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@file
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The functions in this file relate to the allocation of available bits to
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subbands within the SBC/eSBC frame, along with support functions for computing
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frame length and bitrate.
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@ingroup codec_internal
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*/
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/**
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@addtogroup codec_internal
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@{
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*/
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#include <oi_codec_sbc_private.h>
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#include "oi_utils.h"
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uint32_t OI_SBC_MaxBitpool(OI_CODEC_SBC_FRAME_INFO* frame) {
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switch (frame->mode) {
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case SBC_MONO:
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case SBC_DUAL_CHANNEL:
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return 16 * frame->nrof_subbands;
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case SBC_STEREO:
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case SBC_JOINT_STEREO:
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return 32 * frame->nrof_subbands;
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}
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ERROR(("Invalid frame mode %d", frame->mode));
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OI_ASSERT(false);
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return 0; /* Should never be reached */
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}
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PRIVATE uint16_t internal_CalculateFramelen(OI_CODEC_SBC_FRAME_INFO* frame) {
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uint16_t nbits = frame->nrof_blocks * frame->bitpool;
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uint16_t nrof_subbands = frame->nrof_subbands;
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uint16_t result = nbits;
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if (frame->mode == SBC_JOINT_STEREO) {
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result += nrof_subbands + (8 * nrof_subbands);
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} else {
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if (frame->mode == SBC_DUAL_CHANNEL) {
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result += nbits;
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}
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if (frame->mode == SBC_MONO) {
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result += 4 * nrof_subbands;
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} else {
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result += 8 * nrof_subbands;
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}
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}
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return SBC_HEADER_LEN + (result + 7) / 8;
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}
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PRIVATE uint32_t internal_CalculateBitrate(OI_CODEC_SBC_FRAME_INFO* frame) {
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OI_UINT blocksbands;
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blocksbands = frame->nrof_subbands * frame->nrof_blocks;
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return DIVIDE(8 * internal_CalculateFramelen(frame) * frame->frequency,
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blocksbands);
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}
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INLINE uint16_t OI_SBC_CalculateFrameAndHeaderlen(
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OI_CODEC_SBC_FRAME_INFO* frame, OI_UINT* headerLen_) {
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OI_UINT headerLen =
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SBC_HEADER_LEN + frame->nrof_subbands * frame->nrof_channels / 2;
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if (frame->mode == SBC_JOINT_STEREO) {
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headerLen++;
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}
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*headerLen_ = headerLen;
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return internal_CalculateFramelen(frame);
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}
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#define MIN(x, y) ((x) < (y) ? (x) : (y))
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/*
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* Computes the bit need for each sample and as also returns a counts of bit
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* needs that are greater than one. This count is used in the first phase of bit
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* allocation.
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*
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* We also compute a preferred bitpool value that this is the minimum bitpool
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* needed to guarantee lossless representation of the audio data. The preferred
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* bitpool may be larger than the bits actually required but the only input we
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* have are the scale factors. For example, it takes 2 bits to represent values
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* in the range -1 .. +1 but the scale factor is 0. To guarantee lossless
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* representation we add 2 to each scale factor and sum them to come up with the
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* preferred bitpool. This is not ideal because 0 requires 0 bits but we
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* currently have no way of knowing this.
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*
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* @param bitneed Array to return bitneeds for each subband
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*
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* @param ch Channel 0 or 1
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*
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* @param preferredBitpool Returns the number of reserved bits
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*
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* @return The SBC bit need
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*
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*/
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OI_UINT computeBitneed(OI_CODEC_SBC_COMMON_CONTEXT* common, uint8_t* bitneeds,
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OI_UINT ch, OI_UINT* preferredBitpool) {
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static const int8_t offset4[4][4] = {
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{-1, 0, 0, 0}, {-2, 0, 0, 1}, {-2, 0, 0, 1}, {-2, 0, 0, 1}};
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static const int8_t offset8[4][8] = {{-2, 0, 0, 0, 0, 0, 0, 1},
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{-3, 0, 0, 0, 0, 0, 1, 2},
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{-4, 0, 0, 0, 0, 0, 1, 2},
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{-4, 0, 0, 0, 0, 0, 1, 2}};
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const OI_UINT nrof_subbands = common->frameInfo.nrof_subbands;
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OI_UINT sb;
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int8_t* scale_factor = &common->scale_factor[ch ? nrof_subbands : 0];
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OI_UINT bitcount = 0;
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uint8_t maxBits = 0;
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uint8_t prefBits = 0;
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if (common->frameInfo.alloc == SBC_SNR) {
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for (sb = 0; sb < nrof_subbands; sb++) {
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OI_INT bits = scale_factor[sb];
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if (bits > maxBits) {
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maxBits = bits;
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}
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bitneeds[sb] = bits;
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if (bitneeds[sb] > 1) {
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bitcount += bits;
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}
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prefBits += 2 + bits;
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}
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} else {
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const int8_t* offset;
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if (nrof_subbands == 4) {
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offset = offset4[common->frameInfo.freqIndex];
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} else {
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offset = offset8[common->frameInfo.freqIndex];
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}
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for (sb = 0; sb < nrof_subbands; sb++) {
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OI_INT bits = scale_factor[sb];
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if (bits > maxBits) {
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maxBits = bits;
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}
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prefBits += 2 + bits;
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if (bits) {
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bits -= offset[sb];
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if (bits > 0) {
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bits /= 2;
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}
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bits += 5;
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}
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bitneeds[sb] = bits;
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if (bitneeds[sb] > 1) {
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bitcount += bits;
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}
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}
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}
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common->maxBitneed = OI_MAX(maxBits, common->maxBitneed);
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*preferredBitpool += prefBits;
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return bitcount;
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}
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/*
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* Explanation of the adjustToFitBitpool inner loop.
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*
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* The inner loop computes the effect of adjusting the bit allocation up or
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* down. Allocations must be 0 or in the range 2..16. This is accomplished by
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* the following code:
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*
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* for (s = bands - 1; s >= 0; --s) {
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* OI_INT bits = bitadjust + bitneeds[s];
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* bits = bits < 2 ? 0 : bits;
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* bits = bits > 16 ? 16 : bits;
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* count += bits;
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* }
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*
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* This loop can be optimized to perform 4 operations at a time as follows:
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*
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* Adjustment is computed as a 7 bit signed value and added to the bitneed.
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*
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* Negative allocations are zeroed by masking. (n & 0x40) >> 6 puts the
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* sign bit into bit 0, adding this to 0x7F give us a mask of 0x80
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* for -ve values and 0x7F for +ve values.
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*
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* n &= 0x7F + (n & 0x40) >> 6)
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*
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* Allocations greater than 16 are truncated to 16. Adjusted allocations are in
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* the range 0..31 so we know that bit 4 indicates values >= 16. We use this bit
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* to create a mask that zeroes bits 0 .. 3 if bit 4 is set.
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*
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* n &= (15 + (n >> 4))
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*
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* Allocations of 1 are disallowed. Add and shift creates a mask that
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* eliminates the illegal value
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*
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* n &= ((n + 14) >> 4) | 0x1E
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*
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* These operations can be performed in 8 bits without overflowing so we can
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* operate on 4 values at once.
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*/
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/*
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* Encoder/Decoder
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*
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* Computes adjustment +/- of bitneeds to fill bitpool and returns overall
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* adjustment and excess bits.
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*
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* @param bitpool The bitpool we have to work within
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*
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* @param bitneeds An array of bit needs (more acturately allocation
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* prioritities) for each subband across all blocks in the SBC
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* frame
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*
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* @param subbands The number of subbands over which the adkustment is
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* calculated. For mono and dual mode this is 4 or 8, for
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* stereo or joint stereo this is 8 or 16.
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*
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* @param bitcount A starting point for the adjustment
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*
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* @param excess Returns the excess bits after the adjustment
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*
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* @return The adjustment.
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*/
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OI_INT adjustToFitBitpool(const OI_UINT bitpool, uint32_t* bitneeds,
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const OI_UINT subbands, OI_UINT bitcount,
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OI_UINT* excess) {
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OI_INT maxBitadjust = 0;
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OI_INT bitadjust = (bitcount > bitpool) ? -8 : 8;
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OI_INT chop = 8;
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/*
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* This is essentially a binary search for the optimal adjustment value.
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*/
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while ((bitcount != bitpool) && chop) {
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uint32_t total = 0;
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OI_UINT count;
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uint32_t adjust4;
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OI_INT i;
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adjust4 = bitadjust & 0x7F;
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adjust4 |= (adjust4 << 8);
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adjust4 |= (adjust4 << 16);
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for (i = (subbands / 4 - 1); i >= 0; --i) {
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uint32_t mask;
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uint32_t n = bitneeds[i] + adjust4;
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mask = 0x7F7F7F7F + ((n & 0x40404040) >> 6);
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n &= mask;
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mask = 0x0F0F0F0F + ((n & 0x10101010) >> 4);
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n &= mask;
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mask = (((n + 0x0E0E0E0E) >> 4) | 0x1E1E1E1E);
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n &= mask;
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total += n;
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}
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count = (total & 0xFFFF) + (total >> 16);
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count = (count & 0xFF) + (count >> 8);
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chop >>= 1;
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if (count > bitpool) {
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bitadjust -= chop;
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} else {
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maxBitadjust = bitadjust;
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bitcount = count;
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bitadjust += chop;
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}
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}
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*excess = bitpool - bitcount;
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return maxBitadjust;
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}
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/*
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* The bit allocator trys to avoid single bit allocations except as a last
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* resort. So in the case where a bitneed of 1 was passed over during the
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* adsjustment phase 2 bits are now allocated.
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*/
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INLINE OI_INT allocAdjustedBits(uint8_t* dest, OI_INT bits, OI_INT excess) {
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if (bits < 16) {
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if (bits > 1) {
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if (excess) {
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++bits;
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--excess;
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}
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} else if ((bits == 1) && (excess > 1)) {
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bits = 2;
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excess -= 2;
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} else {
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bits = 0;
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}
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} else {
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bits = 16;
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}
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*dest = (uint8_t)bits;
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return excess;
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}
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/*
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* Excess bits not allocated by allocaAdjustedBits are allocated round-robin.
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*/
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INLINE OI_INT allocExcessBits(uint8_t* dest, OI_INT excess) {
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if (*dest < 16) {
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*dest += 1;
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return excess - 1;
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} else {
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return excess;
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}
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}
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void oneChannelBitAllocation(OI_CODEC_SBC_COMMON_CONTEXT* common,
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BITNEED_UNION1* bitneeds, OI_UINT ch,
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OI_UINT bitcount) {
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const uint8_t nrof_subbands = common->frameInfo.nrof_subbands;
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OI_UINT excess;
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OI_UINT sb;
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OI_INT bitadjust;
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uint8_t RESTRICT* allocBits;
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{
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OI_UINT ex;
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bitadjust = adjustToFitBitpool(common->frameInfo.bitpool, bitneeds->uint32,
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nrof_subbands, bitcount, &ex);
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/* We want the compiler to put excess into a register */
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excess = ex;
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}
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/*
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* Allocate adjusted bits
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*/
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allocBits = &common->bits.uint8[ch ? nrof_subbands : 0];
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sb = 0;
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while (sb < nrof_subbands) {
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excess = allocAdjustedBits(&allocBits[sb], bitneeds->uint8[sb] + bitadjust,
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excess);
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++sb;
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}
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sb = 0;
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while (excess) {
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excess = allocExcessBits(&allocBits[sb], excess);
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++sb;
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}
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}
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void monoBitAllocation(OI_CODEC_SBC_COMMON_CONTEXT* common) {
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BITNEED_UNION1 bitneeds;
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OI_UINT bitcount;
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OI_UINT bitpoolPreference = 0;
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bitcount = computeBitneed(common, bitneeds.uint8, 0, &bitpoolPreference);
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oneChannelBitAllocation(common, &bitneeds, 0, bitcount);
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}
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/**
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@}
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*/
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