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
28 The functions in this file relate to the allocation of available bits to
29 subbands within the SBC/eSBC frame, along with support functions for computing
30 frame 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
OI_SBC_MaxBitpool(OI_CODEC_SBC_FRAME_INFO * frame)43 uint32_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
internal_CalculateFramelen(OI_CODEC_SBC_FRAME_INFO * frame)58 PRIVATE 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
internal_CalculateBitrate(OI_CODEC_SBC_FRAME_INFO * frame)78 PRIVATE 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
OI_SBC_CalculateFrameAndHeaderlen(OI_CODEC_SBC_FRAME_INFO * frame,OI_UINT * headerLen_)86 INLINE 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 */
computeBitneed(OI_CODEC_SBC_COMMON_CONTEXT * common,uint8_t * bitneeds,OI_UINT ch,OI_UINT * preferredBitpool)124 OI_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 */
adjustToFitBitpool(const OI_UINT bitpool,uint32_t * bitneeds,const OI_UINT subbands,OI_UINT bitcount,OI_UINT * excess)245 OI_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 */
allocAdjustedBits(uint8_t * dest,OI_INT bits,OI_INT excess)300 INLINE 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 */
allocExcessBits(uint8_t * dest,OI_INT excess)323 INLINE 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
oneChannelBitAllocation(OI_CODEC_SBC_COMMON_CONTEXT * common,BITNEED_UNION1 * bitneeds,OI_UINT ch,OI_UINT bitcount)332 void 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
monoBitAllocation(OI_CODEC_SBC_COMMON_CONTEXT * common)367 void 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