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Caching log2_frac(N, BITRES) in the more data to save some CPU

--- a/libcelt/dump_modes.c

+++ b/libcelt/dump_modes.c

@@ -121,6 +121,14 @@

       fprintf(file, "#endif\n");

       fprintf(file, "\n");

+      fprintf(file, "#ifndef DEF_LOGN%d_%d\n", mode->Fs, mode->mdctSize);

+      fprintf(file, "#define DEF_LOGN%d_%d\n", mode->Fs, mode->mdctSize);

+      fprintf (file, "static const celt_int16 logN%d_%d[%d] = {\n", mode->Fs, mode->mdctSize, mode->nbEBands);

+      for (j=0;j<mode->nbEBands;j++)

+         fprintf (file, "%d, ", mode->logN[j]);

+      fprintf (file, "};\n");

+      fprintf(file, "#endif\n");

+      fprintf(file, "\n");

       fprintf(file, "static const CELTMode mode%d_%d_%d = {\n", mode->Fs, mode->mdctSize, mode->overlap);

       fprintf(file, "0x%x,\t/* marker */\n", 0xa110ca7e);

@@ -141,6 +149,7 @@

       fprintf(file, "{%d, 0, 0},\t/* shortMdct */\n", 2*mode->mdctSize);

       fprintf(file, "window%d,\t/* shortWindow */\n", mode->overlap);

       fprintf(file, "0,\t/* prob */\n");

+      fprintf(file, "logN%d_%d,\t/* logN */\n", mode->Fs, mode->mdctSize);

       fprintf(file, "0x%x,\t/* marker */\n", 0xa110ca7e);

       fprintf(file, "};\n");

    }

--- a/libcelt/modes.c

+++ b/libcelt/modes.c

@@ -273,6 +273,7 @@

    int res;

    CELTMode *mode=NULL;

    celt_word16 *window;

+   celt_int16 *logN;

    ALLOC_STACK;

 #if !defined(VAR_ARRAYS) && !defined(USE_ALLOCA)

    if (global_stack==NULL)

@@ -367,6 +368,13 @@

    if (mode->bits==NULL)

       goto failure;

+   logN = (celt_int16*)celt_alloc(mode->nbEBands*sizeof(celt_int16));

+   if (logN==NULL)

+      goto failure;

+

+   for (i=0;i<mode->nbEBands;i++)

+      logN[i] = log2_frac(mode->eBands[i+1]-mode->eBands[i], BITRES);

+   mode->logN = logN;

 #endif /* !STATIC_MODES */

    clt_mdct_init(&mode->mdct, 2*mode->mdctSize);

--- a/libcelt/modes.h

+++ b/libcelt/modes.h

@@ -106,6 +106,7 @@

    const celt_word16 *shortWindow;

    int *prob;

+   const celt_int16 *logN;

    celt_uint32 marker_end;

 };

--- a/libcelt/rate.c

+++ b/libcelt/rate.c

@@ -148,7 +148,7 @@

       N=m->eBands[j+1]-m->eBands[j]; 

       /* Compensate for the extra DoF in stereo */

       d=(C*N+ ((C==2 && N>2) ? 1 : 0))<<BITRES; 

-      offset = FINE_OFFSET - log2_frac(N, BITRES);

+      offset = FINE_OFFSET - m->logN[j];

       /* Offset for the number of fine bits compared to their "fair share" of total/N */

       offset = bits[j]-offset*N*C;

       /* Compensate for the prediction gain in stereo */