opus: slight speedup of deemphasis

Hoist load of coefficients out of the loop.

Speeds up decoding of a 64kbps test file by 0.6MHz on h300 (cf)
0.2MHz on c200 (pp) and 0.1MHz on fuzev1 (amsv1)

Signed-off-by: Nils Wallménius <nils@rockbox.org>

Change-Id: I4be0059fc2a77748575f5fc9378f7f348d64f1c4

1 files changed, 8 insertions, 3 deletions

diff --git a/lib/rbcodec/codecs/libopus/celt/celt.c b/lib/rbcodec/codecs/libopus/celt/celt.c
index a4e5131a04..4a09cc9905 100644
--- a/lib/rbcodec/codecs/libopus/celt/celt.c
+++ b/lib/rbcodec/codecs/libopus/celt/celt.c
@@ -466,16 +466,21 @@ static void deemphasis(celt_sig *in[], opus_val16 *pcm, int N, int C, /* int dow
       int j;
       celt_sig * OPUS_RESTRICT x;
       opus_val16  * OPUS_RESTRICT y;
+      opus_val16 coef0 = coef[0];
+#ifdef CUSTOM_MODES
+      opus_val16 coef1 = coef[1];
+      opus_val16 coef3 = coef[3];
+#endif
       celt_sig m = mem[c];
       x =in[c];
       y = pcm+c;
       for (j=0;j<N;j++)
       {
          celt_sig tmp = *x + m;
-         m = MULT16_32_Q15(coef[0], tmp);
+         m = MULT16_32_Q15(coef0, tmp);
 #ifdef CUSTOM_MODES
-         m -= MULT16_32_Q15(coef[1], *x);
-         tmp = SHL32(MULT16_32_Q15(coef[3], tmp), 2);
+         m -= MULT16_32_Q15(coef1, *x);
+         tmp = SHL32(MULT16_32_Q15(coef3, tmp), 2);
 #endif
          x++;
          /* Technically the store could be moved outside of the if because