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controlling rounding

--- a/celt/bands.c

+++ b/celt/bands.c

@@ -658,6 +658,7 @@

    const celt_ener *bandE;

    opus_uint32 seed;

    int arch;

+   int theta_round;

 };

 struct split_ctx {

@@ -715,8 +716,14 @@

    if (qn!=1)

    {

       if (encode)

-         itheta = (itheta*(opus_int32)qn+8192)>>14;

-

+      {

+         if (!stereo || ctx->theta_round == 0)

+            itheta = (itheta*(opus_int32)qn+8192)>>14;

+         else if (ctx->theta_round < 0)

+            itheta = (itheta*(opus_int32)qn)>>14;

+         else

+            itheta = (itheta*(opus_int32)qn+16383)>>14;

+      }

       /* Entropy coding of the angle. We use a uniform pdf for the

          time split, a step for stereo, and a triangular one for the rest. */

       if (stereo && N>2)

@@ -1482,6 +1489,7 @@

       } else {

          if (Y!=NULL)

          {

+            ctx.theta_round = 0;

             x_cm = quant_band_stereo(&ctx, X, Y, N, b, B,

                   effective_lowband != -1 ? norm+effective_lowband : NULL, LM,

                   last?NULL:norm+M*eBands[i]-norm_offset, lowband_scratch, x_cm|y_cm);