libAACdec/src/ldfiltbank.cpp

   1
   2 /* -----------------------------------------------------------------------------------------------------------
   3 Software License for The Fraunhofer FDK AAC Codec Library for Android
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   5 © Copyright  1995 - 2013 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
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   8  1.    INTRODUCTION
   9 The Fraunhofer FDK AAC Codec Library for Android ("FDK AAC Codec") is software that implements
  10 the MPEG Advanced Audio Coding ("AAC") encoding and decoding scheme for digital audio.
  11 This FDK AAC Codec software is intended to be used on a wide variety of Android devices.
  12
  13 AAC's HE-AAC and HE-AAC v2 versions are regarded as today's most efficient general perceptual
  14 audio codecs. AAC-ELD is considered the best-performing full-bandwidth communications codec by
  15 independent studies and is widely deployed. AAC has been standardized by ISO and IEC as part
  16 of the MPEG specifications.
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  73 5.    CONTACT INFORMATION
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  75 Fraunhofer Institute for Integrated Circuits IIS
  76 Attention: Audio and Multimedia Departments - FDK AAC LL
  77 Am Wolfsmantel 33
  78 91058 Erlangen, Germany
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  82 ----------------------------------------------------------------------------------------------------------- */
  83
  84 /***************************************************************************\
  85 *
  86  *   filename: ldfiltbank.c
  87  *   project : MPEG-4 Audio Decoder
  88  *   contents/description: low delay filterbank
  89  *
  90 \***************************************************************************/
  91
  92 #include "ldfiltbank.h"
  93
  94
  95 #include "aac_rom.h"
  96 #include "dct.h"
  97 #include "FDK_tools_rom.h"
  98 #include "mdct.h"
  99
 100 #define LDFB_HEADROOM 2
 101
 102 static void multE2_DinvF_fdk(INT_PCM *output, FIXP_DBL* x, const FIXP_WTB* fb, FIXP_DBL* z, const int N, const int  stride)
 103 {
 104   int i, scale;
 105
 106   /*  scale for FIXP_DBL -> INT_PCM conversion. */
 107   scale = (DFRACT_BITS - SAMPLE_BITS) - LDFB_HEADROOM;
 108
 109   for(i=0;i<N/4;i++)
 110   {
 111     FIXP_DBL z0, z2, tmp;
 112
 113     z2 = x[N/2+i];
 114     z0 = z2 + ( fMultDiv2(z[N/2+i], fb[2*N + i]) >> (-WTS2-1) );
 115
 116     z[N/2+i] = x[N/2-1-i] + ( fMultDiv2(z[N + i], fb[2*N + N/2 + i]) >> (-WTS2-1) );
 117
 118     tmp = ( fMultDiv2(z[N/2+i], fb[N+N/2-1-i]) + fMultDiv2(z[i], fb[N+N/2+i]) ) ;
 119
 120 #if (SAMPLE_BITS <= 16)
 121     FDK_ASSERT( (-WTS1-1 + scale) >= 0);
 122     output[(N*3/4-1-i)*stride] = (INT_PCM)SATURATE_RIGHT_SHIFT(tmp, -WTS1-1 + scale, SAMPLE_BITS);
 123 #else
 124     FDK_ASSERT( (WTS1+1 - scale) >= 0);
 125     output[(N*3/4-1-i)*stride] = (INT_PCM)SATURATE_LEFT_SHIFT(tmp, WTS1+1 - scale, SAMPLE_BITS);
 126 #endif
 127
 128     z[i] = z0;
 129     z[N + i] = z2;
 130   }
 131
 132   for(i=N/4;i<N/2;i++)
 133   {
 134     FIXP_DBL z0, z2, tmp0, tmp1;
 135
 136     z2 = x[N/2+i];
 137     z0 = z2 + ( fMultDiv2(z[N/2+i], fb[2*N + i]) >> (-WTS2-1) );
 138
 139     z[N/2+i] = x[N/2-1-i] + ( fMultDiv2(z[N + i], fb[2*N + N/2 + i]) >> (-WTS2-1) );
 140
 141     tmp0 = ( fMultDiv2(z[N/2+i], fb[N/2-1-i])   + fMultDiv2(z[i], fb[N/2+i])   ) ;
 142     tmp1 = ( fMultDiv2(z[N/2+i], fb[N+N/2-1-i]) + fMultDiv2(z[i], fb[N+N/2+i]) ) ;
 143
 144 #if (SAMPLE_BITS <= 16)
 145     FDK_ASSERT( (-WTS0-1 + scale) >= 0);
 146     output[(i-N/4)*stride]     = (INT_PCM)SATURATE_RIGHT_SHIFT(tmp0, -WTS0-1 + scale, SAMPLE_BITS);
 147     output[(N*3/4-1-i)*stride] = (INT_PCM)SATURATE_RIGHT_SHIFT(tmp1, -WTS1-1 + scale, SAMPLE_BITS);
 148 #else
 149     FDK_ASSERT( (WTS0+1 - scale) >= 0);
 150     output[(i-N/4)*stride]     = (INT_PCM)SATURATE_LEFT_SHIFT(tmp0, WTS0+1 - scale, SAMPLE_BITS);
 151     output[(N*3/4-1-i)*stride] = (INT_PCM)SATURATE_LEFT_SHIFT(tmp1, WTS1+1 - scale, SAMPLE_BITS);
 152 #endif
 153     z[i] = z0;
 154     z[N + i] = z2;
 155   }
 156
 157   /* Exchange quarter parts of x to bring them in the "right" order */
 158   for(i=0;i<N/4;i++)
 159   {
 160     FIXP_DBL tmp0 = fMultDiv2(z[i], fb[N/2+i]);
 161
 162 #if (SAMPLE_BITS <= 16)
 163     FDK_ASSERT( (-WTS0-1 + scale) >= 0);
 164     output[(N*3/4 + i)*stride] = (INT_PCM)SATURATE_RIGHT_SHIFT(tmp0, -WTS0-1 + scale, SAMPLE_BITS);
 165 #else
 166     FDK_ASSERT( (WTS0+1 - scale) >= 0);
 167     output[(N*3/4 + i)*stride] = (INT_PCM)SATURATE_LEFT_SHIFT(tmp0, WTS0+1 - scale, SAMPLE_BITS);
 168 #endif
 169   }
 170 }
 171
 172 int InvMdctTransformLowDelay_fdk (FIXP_DBL *mdctData, const int mdctData_e, INT_PCM *output, FIXP_DBL *fs_buffer, const int stride, const int N) {
 173
 174   const FIXP_WTB *coef;
 175   FIXP_DBL gain = (FIXP_DBL)0;
 176   int scale = mdctData_e + MDCT_OUT_HEADROOM - LDFB_HEADROOM; /* The LDFB_HEADROOM is compensated inside multE2_DinvF_fdk() below */
 177
 178   /* Select LD window slope */
 179   if (N == 512)
 180     coef = (FIXP_WTB*)LowDelaySynthesis512;
 181   else
 182     coef = (FIXP_WTB*)LowDelaySynthesis480;
 183
 184   /*
 185      Apply exponent and 1/N factor.
 186      Note: "scale" is off by one because for LD_MDCT the window length is twice
 187      the window length of a regular MDCT. This is corrected inside multE2_DinvF_fdk().
 188      Refer to ISO/IEC 14496-3:2009 page 277, chapter 4.6.20.2 "Low Delay Window".
 189    */
 190   imdct_gain(&gain, &scale, N);
 191
 192   dct_IV(mdctData, N, &scale);
 193
 194   if (gain != (FIXP_DBL)0) {
 195     scaleValuesWithFactor(mdctData, gain, N, scale);
 196   } else {
 197     scaleValues(mdctData, N, scale);
 198   }
 199
 200   /* Since all exponent and factors have been applied, current exponent is zero. */
 201   multE2_DinvF_fdk(output, mdctData, coef, fs_buffer, N, stride);
 202
 203   return (1);
 204 }
 205
 206
 207
 208