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fixed-point: simplification of the gain in mix_pitch_and_residual()

--- a/libcelt/bands.c

+++ b/libcelt/bands.c

@@ -196,7 +196,7 @@

 void renormalise_bands(const CELTMode *m, celt_norm_t *X)

 {

-   VARDECL(celt_ener_t *tmpE);

+   VARDECL(celt_ener_t, tmpE);

    SAVE_STACK;

    ALLOC(tmpE, m->nbEBands*m->nbChannels, celt_ener_t);

    compute_band_energies(m, X, tmpE);

--- a/libcelt/vq.c

+++ b/libcelt/vq.c

@@ -85,10 +85,14 @@

       Ryy = MAC16_16(Ryy, y[i],y[i]);

    /* g = (sqrt(Ryp^2 + Ryy - Rpp*Ryy)-Ryp)/Ryy */

-   g = DIV32(SHL32(celt_sqrt(MULT16_16(ROUND(Ryp,14),ROUND(Ryp,14)) + Ryy - MULT16_16(ROUND(Ryy,14),ROUND(Rpp,14))) - ROUND(Ryp,14),14),ROUND(Ryy,14));

+   g = MULT16_32_Q15(

+            celt_sqrt(MULT16_16(ROUND(Ryp,14),ROUND(Ryp,14)) + Ryy -

+                      MULT16_16(ROUND(Ryy,14),ROUND(Rpp,14)))

+            - ROUND(Ryp,14),

+       celt_rcp(SHR32(Ryy,9)));

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

-      X[i] = P[i] + MULT16_32_Q14(y[i], g);

+      X[i] = P[i] + ROUND(MULT16_16(y[i], g),11);

    RESTORE_STACK;

 }