1/* 2 * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11/****************************************************************** 12 13 iLBC Speech Coder ANSI-C Source Code 14 15 WebRtcIlbcfix_GainQuant.c 16 17******************************************************************/ 18 19#include "defines.h" 20#include "constants.h" 21 22/*----------------------------------------------------------------* 23 * quantizer for the gain in the gain-shape coding of residual 24 *---------------------------------------------------------------*/ 25 26int16_t WebRtcIlbcfix_GainQuant( /* (o) quantized gain value */ 27 int16_t gain, /* (i) gain value Q14 */ 28 int16_t maxIn, /* (i) maximum of gain value Q14 */ 29 int16_t stage, /* (i) The stage of the search */ 30 int16_t *index /* (o) quantization index */ 31 ) { 32 33 int16_t scale, cblen; 34 int32_t gainW32, measure1, measure2; 35 const int16_t *cbPtr, *cb; 36 int loc, noMoves, noChecks, i; 37 38 /* ensure a lower bound (0.1) on the scaling factor */ 39 40 scale = WEBRTC_SPL_MAX(1638, maxIn); 41 42 /* select the quantization table and calculate 43 the length of the table and the number of 44 steps in the binary search that are needed */ 45 cb = WebRtcIlbcfix_kGain[stage]; 46 cblen = 32>>stage; 47 noChecks = 4-stage; 48 49 /* Multiply the gain with 2^14 to make the comparison 50 easier and with higher precision */ 51 gainW32 = gain << 14; 52 53 /* Do a binary search, starting in the middle of the CB 54 loc - defines the current position in the table 55 noMoves - defines the number of steps to move in the CB in order 56 to get next CB location 57 */ 58 59 loc = cblen>>1; 60 noMoves = loc; 61 cbPtr = cb + loc; /* Centre of CB */ 62 63 for (i=noChecks;i>0;i--) { 64 noMoves>>=1; 65 measure1 = scale * *cbPtr; 66 67 /* Move up if gain is larger, otherwise move down in table */ 68 measure1 = measure1 - gainW32; 69 70 if (0>measure1) { 71 cbPtr+=noMoves; 72 loc+=noMoves; 73 } else { 74 cbPtr-=noMoves; 75 loc-=noMoves; 76 } 77 } 78 79 /* Check which value is the closest one: loc-1, loc or loc+1 */ 80 81 measure1 = scale * *cbPtr; 82 if (gainW32>measure1) { 83 /* Check against value above loc */ 84 measure2 = scale * cbPtr[1]; 85 if ((measure2-gainW32)<(gainW32-measure1)) { 86 loc+=1; 87 } 88 } else { 89 /* Check against value below loc */ 90 measure2 = scale * cbPtr[-1]; 91 if ((gainW32-measure2)<=(measure1-gainW32)) { 92 loc-=1; 93 } 94 } 95 96 /* Guard against getting outside the table. The calculation above can give a location 97 which is one above the maximum value (in very rare cases) */ 98 loc=WEBRTC_SPL_MIN(loc, (cblen-1)); 99 *index=loc; 100 101 /* Calculate and return the quantized gain value (in Q14) */ 102 return (int16_t)((scale * cb[loc] + 8192) >> 14); 103} 104