fixed-point: slight (but free) accuracy improvement in compute_band_energies()

Also moves the VSHR32() condition outside the loop just in case some compilers
don't optimize that properly.

3 files changed, 24 insertions, 19 deletions

diff --git a/celt/bands.c b/celt/bands.c
index 73346445..ee230912 100644
--- a/celt/bands.c
+++ b/celt/bands.c
@@ -92,11 +92,11 @@ static int bitexact_log2tan(int isin,int icos)
 
 #ifdef FIXED_POINT
 /* Compute the amplitude (sqrt energy) in each of the bands */
-void compute_band_energies(const CELTMode *m, const celt_sig *X, celt_ener *bandE, int end, int C, int M)
+void compute_band_energies(const CELTMode *m, const celt_sig *X, celt_ener *bandE, int end, int C, int LM)
 {
    int i, c, N;
    const opus_int16 *eBands = m->eBands;
-   N = M*m->shortMdctSize;
+   N = m->shortMdctSize<<LM;
    c=0; do {
       for (i=0;i<end;i++)
       {
@@ -104,18 +104,23 @@ void compute_band_energies(const CELTMode *m, const celt_sig *X, celt_ener *band
          opus_val32 maxval=0;
          opus_val32 sum = 0;
 
-         j=M*eBands[i]; do {
-            maxval = MAX32(maxval, X[j+c*N]);
-            maxval = MAX32(maxval, -X[j+c*N]);
-         } while (++j<M*eBands[i+1]);
-
+         maxval = celt_maxabs32(&X[c*N+(eBands[i]<<LM)], (eBands[i+1]-eBands[i])<<LM);
          if (maxval > 0)
          {
-            int shift = celt_ilog2(maxval)-10;
-            j=M*eBands[i]; do {
-               sum = MAC16_16(sum, EXTRACT16(VSHR32(X[j+c*N],shift)),
-                                   EXTRACT16(VSHR32(X[j+c*N],shift)));
-            } while (++j<M*eBands[i+1]);
+            int shift = celt_ilog2(maxval) - 14 + (((m->logN[i]>>BITRES)+LM+1)>>1);
+            j=eBands[i]<<LM;
+            if (shift>0)
+            {
+               do {
+                  sum = MAC16_16(sum, EXTRACT16(SHR32(X[j+c*N],shift)),
+                        EXTRACT16(SHR32(X[j+c*N],shift)));
+               } while (++j<eBands[i+1]<<LM);
+            } else {
+               do {
+                  sum = MAC16_16(sum, EXTRACT16(SHL32(X[j+c*N],-shift)),
+                        EXTRACT16(SHL32(X[j+c*N],-shift)));
+               } while (++j<eBands[i+1]<<LM);
+            }
             /* We're adding one here to ensure the normalized band isn't larger than unity norm */
             bandE[i+c*m->nbEBands] = EPSILON+VSHR32(EXTEND32(celt_sqrt(sum)),-shift);
          } else {
@@ -150,16 +155,16 @@ void normalise_bands(const CELTMode *m, const celt_sig * OPUS_RESTRICT freq, cel
 
 #else /* FIXED_POINT */
 /* Compute the amplitude (sqrt energy) in each of the bands */
-void compute_band_energies(const CELTMode *m, const celt_sig *X, celt_ener *bandE, int end, int C, int M)
+void compute_band_energies(const CELTMode *m, const celt_sig *X, celt_ener *bandE, int end, int C, int LM)
 {
    int i, c, N;
    const opus_int16 *eBands = m->eBands;
-   N = M*m->shortMdctSize;
+   N = m->shortMdctSize<<LM;
    c=0; do {
       for (i=0;i<end;i++)
       {
          opus_val32 sum;
-         sum = 1e-27f + celt_inner_prod(&X[c*N+M*eBands[i]], &X[c*N+M*eBands[i]], M*(eBands[i+1]-eBands[i]));
+         sum = 1e-27f + celt_inner_prod(&X[c*N+(eBands[i]<<LM)], &X[c*N+(eBands[i]<<LM)], (eBands[i+1]-eBands[i])<<LM);
          bandE[i+c*m->nbEBands] = celt_sqrt(sum);
          /*printf ("%f ", bandE[i+c*m->nbEBands]);*/
       }
diff --git a/celt/bands.h b/celt/bands.h
index 053ac8a1..e6ad9c52 100644
--- a/celt/bands.h
+++ b/celt/bands.h
@@ -41,7 +41,7 @@
  * @param X Spectrum
  * @param bandE Square root of the energy for each band (returned)
  */
-void compute_band_energies(const CELTMode *m, const celt_sig *X, celt_ener *bandE, int end, int C, int M);
+void compute_band_energies(const CELTMode *m, const celt_sig *X, celt_ener *bandE, int end, int C, int LM);
 
 /*void compute_noise_energies(const CELTMode *m, const celt_sig *X, const opus_val16 *tonality, celt_ener *bandE);*/
 
diff --git a/celt/celt_encoder.c b/celt/celt_encoder.c
index 1ac00581..8a1c7483 100644
--- a/celt/celt_encoder.c
+++ b/celt/celt_encoder.c
@@ -1519,7 +1519,7 @@ int celt_encode_with_ec(CELTEncoder * OPUS_RESTRICT st, const opus_val16 * pcm,
    if (secondMdct)
    {
       compute_mdcts(mode, 0, in, freq, C, CC, LM, st->upsample);
-      compute_band_energies(mode, freq, bandE, effEnd, C, M);
+      compute_band_energies(mode, freq, bandE, effEnd, C, LM);
       amp2Log2(mode, effEnd, end, bandE, bandLogE2, C);
       for (i=0;i<C*nbEBands;i++)
          bandLogE2[i] += HALF16(SHL16(LM, DB_SHIFT));
@@ -1528,7 +1528,7 @@ int celt_encode_with_ec(CELTEncoder * OPUS_RESTRICT st, const opus_val16 * pcm,
    compute_mdcts(mode, shortBlocks, in, freq, C, CC, LM, st->upsample);
    if (CC==2&&C==1)
       tf_chan = 0;
-   compute_band_energies(mode, freq, bandE, effEnd, C, M);
+   compute_band_energies(mode, freq, bandE, effEnd, C, LM);
 
    if (st->lfe)
    {
@@ -1651,7 +1651,7 @@ int celt_encode_with_ec(CELTEncoder * OPUS_RESTRICT st, const opus_val16 * pcm,
          isTransient = 1;
          shortBlocks = M;
          compute_mdcts(mode, shortBlocks, in, freq, C, CC, LM, st->upsample);
-         compute_band_energies(mode, freq, bandE, effEnd, C, M);
+         compute_band_energies(mode, freq, bandE, effEnd, C, LM);
          amp2Log2(mode, effEnd, end, bandE, bandLogE, C);
          /* Compensate for the scaling of short vs long mdcts */
          for (i=0;i<C*nbEBands;i++)