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optimisation: better indexing/looping in vq_index()

--- a/libcelt/quant_pitch.c

+++ b/libcelt/quant_pitch.c

@@ -54,24 +54,24 @@

 #define Q1515ONE MULT16_16(Q15ONE,Q15ONE)

 /** Taken from Speex.Finds the index of the entry in a codebook that best matches the input*/

-int vq_index(celt_pgain_t *in, const celt_uint16_t *codebook, int len, int entries)

+int vq_index(const celt_pgain_t *in, const celt_uint16_t *codebook, int len, int entries)

 {

    int i,j;

    int ind = 0;

-   celt_word32_t min_dist=0;

+   celt_word32_t min_dist=VERY_LARGE32;

    int best_index=0;

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

    {

       celt_word32_t dist=0;

-      for (j=0;j<len>>1;j++)

-      {

-         celt_pgain_t tmp1 = SHR16(SUB16(in[2*j],PGAIN_EVEN(codebook, ind)),1);

-         celt_pgain_t tmp2 = SHR16(SUB16(in[2*j+1],PGAIN_ODD(codebook, ind)),1);

+      const celt_pgain_t *inp = in;

+      j=0; do {

+         celt_pgain_t tmp1 = SHR16(SUB16(*inp++,PGAIN_EVEN(codebook, ind)),1);

+         celt_pgain_t tmp2 = SHR16(SUB16(*inp++,PGAIN_ODD(codebook, ind)),1);

          ind++;

          dist = MAC16_16(dist, tmp1, tmp1);

          dist = MAC16_16(dist, tmp2, tmp2);

-      }

-      if (i==0 || dist<min_dist)

+      } while (++j<len>>1);

+      if (dist<min_dist)

       {

          min_dist=dist;

          best_index=i;