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quant.c

/********************************************************************
 *                                                                  *
 * THIS FILE IS PART OF THE OggTheora SOFTWARE CODEC SOURCE CODE.   *
 * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
 * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
 * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
 *                                                                  *
 * THE Theora SOURCE CODE IS COPYRIGHT (C) 2002-2007                *
 * by the Xiph.Org Foundation http://www.xiph.org/                  *
 *                                                                  *
 ********************************************************************

  function:
    last mod: $Id: quant.c 13884 2007-09-22 08:38:10Z giles $

 ********************************************************************/

#include <stdlib.h>
#include <string.h>
#include <ogg/ogg.h>
#include "quant.h"



unsigned OC_DC_QUANT_MIN[2]={4<<2,8<<2};
unsigned OC_AC_QUANT_MIN[2]={2<<2,4<<2};



/*Initializes the dequantization tables from a set of quantizer info.
  Currently the dequantizer (and elsewhere enquantizer) tables are expected to
   be initialized as pointing to the storage reserved for them in the
   oc_theora_state (resp. oc_enc_ctx) structure.
  If some tables are duplicates of others, the pointers will be adjusted to
   point to a single copy of the tables, but the storage for them will not be
   freed.
  If you're concerned about the memory footprint, the obvious thing to do is
   to move the storage out of its fixed place in the structures and allocate
   it on demand.
  However, a much, much better option is to only store the quantization
   matrices being used for the current frame, and to recalculate these as the
   qi values change between frames (this is what VP3 did).*/
void oc_dequant_tables_init(oc_quant_table *_dequant[2][3],
 int _pp_dc_scale[64],const th_quant_info *_qinfo){
  int          qti;
  int          pli;
  for(qti=0;qti<2;qti++)for(pli=0;pli<3;pli++){
    int qi;
    int qri;
    /*These simple checks help us improve cache coherency later.*/
    if(pli>0&&memcmp(_qinfo->qi_ranges[qti]+pli-1,
     _qinfo->qi_ranges[qti]+pli,sizeof(_qinfo->qi_ranges[qti][pli]))==0){
      _dequant[qti][pli]=_dequant[qti][pli-1];
      continue;
    }
    if(qti>0&&memcmp(_qinfo->qi_ranges[qti-1]+pli,
     _qinfo->qi_ranges[qti]+pli,sizeof(_qinfo->qi_ranges[qti][pli]))==0){
      _dequant[qti][pli]=_dequant[qti-1][pli];
      continue;
    }
    for(qi=qri=0;qri<=_qinfo->qi_ranges[qti][pli].nranges;qri++){
      th_quant_base base;
      ogg_uint32_t      q;
      int               qi_start;
      int               qi_end;
      int               ci;
      memcpy(base,_qinfo->qi_ranges[qti][pli].base_matrices[qri],
       sizeof(base));
      qi_start=qi;
      if(qri==_qinfo->qi_ranges[qti][pli].nranges)qi_end=qi+1;
      else qi_end=qi+_qinfo->qi_ranges[qti][pli].sizes[qri];
      for(;;){
        ogg_uint32_t qfac;
        /*In the original VP3.2 code, the rounding offset and the size of the
           dead zone around 0 were controlled by a "sharpness" parameter.
          The size of our dead zone is now controlled by the per-coefficient
           quality thresholds returned by our HVS module.
          We round down from a more accurate value when the quality of the
           reconstruction does not fall below our threshold and it saves bits.
          Hence, all of that VP3.2 code is gone from here, and the remaining
           floating point code has been implemented as equivalent integer code
           with exact precision.*/
        /*Scale DC the coefficient from the proper table.*/
        qfac=(ogg_uint32_t)_qinfo->dc_scale[qi]*base[0];
        if(_pp_dc_scale!=NULL)_pp_dc_scale[qi]=(int)(qfac/160);
        q=(qfac/100)<<2;
        q=OC_CLAMPI(OC_DC_QUANT_MIN[qti],q,OC_QUANT_MAX);
        _dequant[qti][pli][qi][0]=(ogg_uint16_t)q;
        /*Now scale AC coefficients from the proper table.*/
        for(ci=1;ci<64;ci++){
          q=((ogg_uint32_t)_qinfo->ac_scale[qi]*base[ci]/100)<<2;
          q=OC_CLAMPI(OC_AC_QUANT_MIN[qti],q,OC_QUANT_MAX);
          _dequant[qti][pli][qi][ci]=(ogg_uint16_t)q;
        }
        if(++qi>=qi_end)break;
        /*Interpolate the next base matrix.*/
        for(ci=0;ci<64;ci++){
          base[ci]=(unsigned char)(
           (2*((qi_end-qi)*_qinfo->qi_ranges[qti][pli].base_matrices[qri][ci]+
           (qi-qi_start)*_qinfo->qi_ranges[qti][pli].base_matrices[qri+1][ci])
           +_qinfo->qi_ranges[qti][pli].sizes[qri])/
           (2*_qinfo->qi_ranges[qti][pli].sizes[qri]));
        }
      }
    }
  }
}

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