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