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Unrolled version of the comb filter for ARM (eliminates MOVs)

--- a/celt/celt.c

+++ b/celt/celt.c

@@ -97,7 +97,7 @@

    x3 = SHL32(x[-T-1], 1);

    x2 = SHL32(x[-T], 1);

    x1 = SHL32(x[-T+1], 1);

-   for (i=0;i<N;i++)

+   for (i=0;i<N-4;i+=5)

    {

       opus_val32 t;

       x0=SHL32(x[i-T+2],1);

@@ -105,12 +105,42 @@

       t = MAC16_32_Q16(t, g11, ADD32(x1,x3));

       t = MAC16_32_Q16(t, g12, ADD32(x0,x4));

       y[i] = t;

+      x4=SHL32(x[i-T+3],1);

+      t = MAC16_32_Q16(x[i+1], g10, x1);

+      t = MAC16_32_Q16(t, g11, ADD32(x0,x2));

+      t = MAC16_32_Q16(t, g12, ADD32(x4,x3));

+      y[i+1] = t;

+      x3=SHL32(x[i-T+4],1);

+      t = MAC16_32_Q16(x[i+2], g10, x0);

+      t = MAC16_32_Q16(t, g11, ADD32(x4,x1));

+      t = MAC16_32_Q16(t, g12, ADD32(x3,x2));

+      y[i+2] = t;

+      x2=SHL32(x[i-T+5],1);

+      t = MAC16_32_Q16(x[i+3], g10, x4);

+      t = MAC16_32_Q16(t, g11, ADD32(x3,x0));

+      t = MAC16_32_Q16(t, g12, ADD32(x2,x1));

+      y[i+3] = t;

+      x1=SHL32(x[i-T+6],1);

+      t = MAC16_32_Q16(x[i+4], g10, x3);

+      t = MAC16_32_Q16(t, g11, ADD32(x2,x4));

+      t = MAC16_32_Q16(t, g12, ADD32(x1,x0));

+      y[i+4] = t;

+   }

+#ifdef CUSTOM_MODES

+   for (;i<N;i++)

+   {

+      opus_val32 t;

+      x0=SHL32(x[i-T+2],1);

+      t = MAC16_32_Q16(x[i], g10, x2);

+      t = MAC16_32_Q16(t, g11, ADD32(x1,x3));

+      t = MAC16_32_Q16(t, g12, ADD32(x0,x4));

+      y[i] = t;

       x4=x3;

       x3=x2;

       x2=x1;

       x1=x0;

    }

-

+#endif

 }

 #else

 static void comb_filter_const(opus_val32 *y, opus_val32 *x, int T, int N,