1/******************************************************************************
2 *
3 *  Copyright (C) 2014 The Android Open Source Project
4 *  Copyright 2003 - 2004 Open Interface North America, Inc. All rights
5 *                        reserved.
6 *
7 *  Licensed under the Apache License, Version 2.0 (the "License");
8 *  you may not use this file except in compliance with the License.
9 *  You may obtain a copy of the License at:
10 *
11 *  http://www.apache.org/licenses/LICENSE-2.0
12 *
13 *  Unless required by applicable law or agreed to in writing, software
14 *  distributed under the License is distributed on an "AS IS" BASIS,
15 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 *  See the License for the specific language governing permissions and
17 *  limitations under the License.
18 *
19 ******************************************************************************/
20
21/*******************************************************************************
22  $Revision: #1 $
23 ******************************************************************************/
24
25/**
26@file
27
28The functions in this file relate to the allocation of available bits to
29subbands within the SBC/eSBC frame, along with support functions for computing
30frame length and bitrate.
31
32@ingroup codec_internal
33*/
34
35/**
36@addtogroup codec_internal
37@{
38*/
39
40#include <oi_codec_sbc_private.h>
41#include "oi_utils.h"
42
43uint32_t OI_SBC_MaxBitpool(OI_CODEC_SBC_FRAME_INFO* frame) {
44  switch (frame->mode) {
45    case SBC_MONO:
46    case SBC_DUAL_CHANNEL:
47      return 16 * frame->nrof_subbands;
48    case SBC_STEREO:
49    case SBC_JOINT_STEREO:
50      return 32 * frame->nrof_subbands;
51  }
52
53  ERROR(("Invalid frame mode %d", frame->mode));
54  OI_ASSERT(false);
55  return 0; /* Should never be reached */
56}
57
58PRIVATE uint16_t internal_CalculateFramelen(OI_CODEC_SBC_FRAME_INFO* frame) {
59  uint16_t nbits = frame->nrof_blocks * frame->bitpool;
60  uint16_t nrof_subbands = frame->nrof_subbands;
61  uint16_t result = nbits;
62
63  if (frame->mode == SBC_JOINT_STEREO) {
64    result += nrof_subbands + (8 * nrof_subbands);
65  } else {
66    if (frame->mode == SBC_DUAL_CHANNEL) {
67      result += nbits;
68    }
69    if (frame->mode == SBC_MONO) {
70      result += 4 * nrof_subbands;
71    } else {
72      result += 8 * nrof_subbands;
73    }
74  }
75  return SBC_HEADER_LEN + (result + 7) / 8;
76}
77
78PRIVATE uint32_t internal_CalculateBitrate(OI_CODEC_SBC_FRAME_INFO* frame) {
79  OI_UINT blocksbands;
80  blocksbands = frame->nrof_subbands * frame->nrof_blocks;
81
82  return DIVIDE(8 * internal_CalculateFramelen(frame) * frame->frequency,
83                blocksbands);
84}
85
86INLINE uint16_t OI_SBC_CalculateFrameAndHeaderlen(
87    OI_CODEC_SBC_FRAME_INFO* frame, OI_UINT* headerLen_) {
88  OI_UINT headerLen =
89      SBC_HEADER_LEN + frame->nrof_subbands * frame->nrof_channels / 2;
90
91  if (frame->mode == SBC_JOINT_STEREO) {
92    headerLen++;
93  }
94
95  *headerLen_ = headerLen;
96  return internal_CalculateFramelen(frame);
97}
98
99#define MIN(x, y) ((x) < (y) ? (x) : (y))
100
101/*
102 * Computes the bit need for each sample and as also returns a counts of bit
103 * needs that are greater than one. This count is used in the first phase of bit
104 * allocation.
105 *
106 * We also compute a preferred bitpool value that this is the minimum bitpool
107 * needed to guarantee lossless representation of the audio data. The preferred
108 * bitpool may be larger than the bits actually required but the only input we
109 * have are the scale factors. For example, it takes 2 bits to represent values
110 * in the range -1 .. +1 but the scale factor is 0. To guarantee lossless
111 * representation we add 2 to each scale factor and sum them to come up with the
112 * preferred bitpool. This is not ideal because 0 requires 0 bits but we
113 * currently have no way of knowing this.
114 *
115 * @param bitneed       Array to return bitneeds for each subband
116 *
117 * @param ch            Channel 0 or 1
118 *
119 * @param preferredBitpool  Returns the number of reserved bits
120 *
121 * @return              The SBC bit need
122 *
123 */
124OI_UINT computeBitneed(OI_CODEC_SBC_COMMON_CONTEXT* common, uint8_t* bitneeds,
125                       OI_UINT ch, OI_UINT* preferredBitpool) {
126  static const int8_t offset4[4][4] = {
127      {-1, 0, 0, 0}, {-2, 0, 0, 1}, {-2, 0, 0, 1}, {-2, 0, 0, 1}};
128
129  static const int8_t offset8[4][8] = {{-2, 0, 0, 0, 0, 0, 0, 1},
130                                       {-3, 0, 0, 0, 0, 0, 1, 2},
131                                       {-4, 0, 0, 0, 0, 0, 1, 2},
132                                       {-4, 0, 0, 0, 0, 0, 1, 2}};
133
134  const OI_UINT nrof_subbands = common->frameInfo.nrof_subbands;
135  OI_UINT sb;
136  int8_t* scale_factor = &common->scale_factor[ch ? nrof_subbands : 0];
137  OI_UINT bitcount = 0;
138  uint8_t maxBits = 0;
139  uint8_t prefBits = 0;
140
141  if (common->frameInfo.alloc == SBC_SNR) {
142    for (sb = 0; sb < nrof_subbands; sb++) {
143      OI_INT bits = scale_factor[sb];
144      if (bits > maxBits) {
145        maxBits = bits;
146      }
147      bitneeds[sb] = bits;
148      if (bitneeds[sb] > 1) {
149        bitcount += bits;
150      }
151      prefBits += 2 + bits;
152    }
153  } else {
154    const int8_t* offset;
155    if (nrof_subbands == 4) {
156      offset = offset4[common->frameInfo.freqIndex];
157    } else {
158      offset = offset8[common->frameInfo.freqIndex];
159    }
160    for (sb = 0; sb < nrof_subbands; sb++) {
161      OI_INT bits = scale_factor[sb];
162      if (bits > maxBits) {
163        maxBits = bits;
164      }
165      prefBits += 2 + bits;
166      if (bits) {
167        bits -= offset[sb];
168        if (bits > 0) {
169          bits /= 2;
170        }
171        bits += 5;
172      }
173      bitneeds[sb] = bits;
174      if (bitneeds[sb] > 1) {
175        bitcount += bits;
176      }
177    }
178  }
179  common->maxBitneed = OI_MAX(maxBits, common->maxBitneed);
180  *preferredBitpool += prefBits;
181  return bitcount;
182}
183
184/*
185 * Explanation of the adjustToFitBitpool inner loop.
186 *
187 * The inner loop computes the effect of adjusting the bit allocation up or
188 * down. Allocations must be 0 or in the range 2..16. This is accomplished by
189 * the following code:
190 *
191 *           for (s = bands - 1; s >= 0; --s) {
192 *              OI_INT bits = bitadjust + bitneeds[s];
193 *              bits = bits < 2 ? 0 : bits;
194 *              bits = bits > 16 ? 16 : bits;
195 *              count += bits;
196 *          }
197 *
198 * This loop can be optimized to perform 4 operations at a time as follows:
199 *
200 * Adjustment is computed as a 7 bit signed value and added to the bitneed.
201 *
202 * Negative allocations are zeroed by masking. (n & 0x40) >> 6 puts the
203 * sign bit into bit 0, adding this to 0x7F give us a mask of 0x80
204 * for -ve values and 0x7F for +ve values.
205 *
206 * n &= 0x7F + (n & 0x40) >> 6)
207 *
208 * Allocations greater than 16 are truncated to 16. Adjusted allocations are in
209 * the range 0..31 so we know that bit 4 indicates values >= 16. We use this bit
210 * to create a mask that zeroes bits 0 .. 3 if bit 4 is set.
211 *
212 * n &= (15 + (n >> 4))
213 *
214 * Allocations of 1 are disallowed. Add and shift creates a mask that
215 * eliminates the illegal value
216 *
217 * n &= ((n + 14) >> 4) | 0x1E
218 *
219 * These operations can be performed in 8 bits without overflowing so we can
220 * operate on 4 values at once.
221 */
222
223/*
224 * Encoder/Decoder
225 *
226 * Computes adjustment +/- of bitneeds to fill bitpool and returns overall
227 * adjustment and excess bits.
228 *
229 * @param bitpool   The bitpool we have to work within
230 *
231 * @param bitneeds  An array of bit needs (more acturately allocation
232 *                  prioritities) for each subband across all blocks in the SBC
233 *                  frame
234 *
235 * @param subbands  The number of subbands over which the adkustment is
236 *                  calculated. For mono and dual mode this is 4 or 8, for
237 *                  stereo or joint stereo this is 8 or 16.
238 *
239 * @param bitcount  A starting point for the adjustment
240 *
241 * @param excess    Returns the excess bits after the adjustment
242 *
243 * @return   The adjustment.
244 */
245OI_INT adjustToFitBitpool(const OI_UINT bitpool, uint32_t* bitneeds,
246                          const OI_UINT subbands, OI_UINT bitcount,
247                          OI_UINT* excess) {
248  OI_INT maxBitadjust = 0;
249  OI_INT bitadjust = (bitcount > bitpool) ? -8 : 8;
250  OI_INT chop = 8;
251
252  /*
253   * This is essentially a binary search for the optimal adjustment value.
254   */
255  while ((bitcount != bitpool) && chop) {
256    uint32_t total = 0;
257    OI_UINT count;
258    uint32_t adjust4;
259    OI_INT i;
260
261    adjust4 = bitadjust & 0x7F;
262    adjust4 |= (adjust4 << 8);
263    adjust4 |= (adjust4 << 16);
264
265    for (i = (subbands / 4 - 1); i >= 0; --i) {
266      uint32_t mask;
267      uint32_t n = bitneeds[i] + adjust4;
268      mask = 0x7F7F7F7F + ((n & 0x40404040) >> 6);
269      n &= mask;
270      mask = 0x0F0F0F0F + ((n & 0x10101010) >> 4);
271      n &= mask;
272      mask = (((n + 0x0E0E0E0E) >> 4) | 0x1E1E1E1E);
273      n &= mask;
274      total += n;
275    }
276
277    count = (total & 0xFFFF) + (total >> 16);
278    count = (count & 0xFF) + (count >> 8);
279
280    chop >>= 1;
281    if (count > bitpool) {
282      bitadjust -= chop;
283    } else {
284      maxBitadjust = bitadjust;
285      bitcount = count;
286      bitadjust += chop;
287    }
288  }
289
290  *excess = bitpool - bitcount;
291
292  return maxBitadjust;
293}
294
295/*
296 * The bit allocator trys to avoid single bit allocations except as a last
297 * resort. So in the case where a bitneed of 1 was passed over during the
298 * adsjustment phase 2 bits are now allocated.
299 */
300INLINE OI_INT allocAdjustedBits(uint8_t* dest, OI_INT bits, OI_INT excess) {
301  if (bits < 16) {
302    if (bits > 1) {
303      if (excess) {
304        ++bits;
305        --excess;
306      }
307    } else if ((bits == 1) && (excess > 1)) {
308      bits = 2;
309      excess -= 2;
310    } else {
311      bits = 0;
312    }
313  } else {
314    bits = 16;
315  }
316  *dest = (uint8_t)bits;
317  return excess;
318}
319
320/*
321 * Excess bits not allocated by allocaAdjustedBits are allocated round-robin.
322 */
323INLINE OI_INT allocExcessBits(uint8_t* dest, OI_INT excess) {
324  if (*dest < 16) {
325    *dest += 1;
326    return excess - 1;
327  } else {
328    return excess;
329  }
330}
331
332void oneChannelBitAllocation(OI_CODEC_SBC_COMMON_CONTEXT* common,
333                             BITNEED_UNION1* bitneeds, OI_UINT ch,
334                             OI_UINT bitcount) {
335  const uint8_t nrof_subbands = common->frameInfo.nrof_subbands;
336  OI_UINT excess;
337  OI_UINT sb;
338  OI_INT bitadjust;
339  uint8_t RESTRICT* allocBits;
340
341  {
342    OI_UINT ex;
343    bitadjust = adjustToFitBitpool(common->frameInfo.bitpool, bitneeds->uint32,
344                                   nrof_subbands, bitcount, &ex);
345    /* We want the compiler to put excess into a register */
346    excess = ex;
347  }
348
349  /*
350   * Allocate adjusted bits
351   */
352  allocBits = &common->bits.uint8[ch ? nrof_subbands : 0];
353
354  sb = 0;
355  while (sb < nrof_subbands) {
356    excess = allocAdjustedBits(&allocBits[sb], bitneeds->uint8[sb] + bitadjust,
357                               excess);
358    ++sb;
359  }
360  sb = 0;
361  while (excess) {
362    excess = allocExcessBits(&allocBits[sb], excess);
363    ++sb;
364  }
365}
366
367void monoBitAllocation(OI_CODEC_SBC_COMMON_CONTEXT* common) {
368  BITNEED_UNION1 bitneeds;
369  OI_UINT bitcount;
370  OI_UINT bitpoolPreference = 0;
371
372  bitcount = computeBitneed(common, bitneeds.uint8, 0, &bitpoolPreference);
373
374  oneChannelBitAllocation(common, &bitneeds, 0, bitcount);
375}
376
377/**
378@}
379*/
380