/*
  * AAC encoder psychoacoustic model
  * Copyright (C) 2008 Konstantin Shishkov
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**

  * @file libavcodec/aacpsy.c

  * AAC encoder psychoacoustic model
  */
 
 #include "avcodec.h"
 #include "aacpsy.h"
 #include "aactab.h"
 
 /***********************************
  *              TODOs:
  * General:
  * better audio preprocessing (add DC highpass filter?)
  * more psy models
  * maybe improve coefficient quantization function in some way
  *
  * 3GPP-based psy model:
  * thresholds linearization after their modifications for attaining given bitrate
  * try other bitrate controlling mechanism (maybe use ratecontrol.c?)
  * control quality for quality-based output
  **********************************/
 
 /**
  * Quantize one coefficient.
  * @return absolute value of the quantized coefficient
  * @see 3GPP TS26.403 5.6.2 "Scalefactor determination"
  */
 static av_always_inline int quant(float coef, const float Q)
 {
     return av_clip((int)(pow(fabsf(coef) * Q, 0.75) + 0.4054), 0, 8191);
 }
 
 static inline float get_approximate_quant_error(float *c, int size, int scale_idx)
 {
     int i;
     int q;
     float coef, unquant, sum = 0.0f;
     const float Q  = ff_aac_pow2sf_tab[200 - scale_idx + SCALE_ONE_POS - SCALE_DIV_512];
     const float IQ = ff_aac_pow2sf_tab[200 + scale_idx - SCALE_ONE_POS + SCALE_DIV_512];
     for(i = 0; i < size; i++){
         coef = fabs(c[i]);
         q = quant(c[i], Q);
         unquant = (q * cbrt(q)) * IQ;
         sum += (coef - unquant) * (coef - unquant);
     }
     return sum;
 }
 
 /**
  * constants for 3GPP AAC psychoacoustic model
  * @{
  */
 #define PSY_3GPP_SPREAD_LOW  1.5f // spreading factor for ascending threshold spreading  (15 dB/Bark)
 #define PSY_3GPP_SPREAD_HI   3.0f // spreading factor for descending threshold spreading (30 dB/Bark)
 /**
  * @}
  */
 
 /**
  * information for single band used by 3GPP TS26.403-inspired psychoacoustic model
  */
 typedef struct Psy3gppBand{
     float energy;    ///< band energy
     float ffac;      ///< form factor
 }Psy3gppBand;
 
 /**
  * psychoacoustic model frame type-dependent coefficients
  */
 typedef struct Psy3gppCoeffs{
     float ath       [64]; ///< absolute threshold of hearing per bands
     float barks     [64]; ///< Bark value for each spectral band in long frame
     float spread_low[64]; ///< spreading factor for low-to-high threshold spreading in long frame
     float spread_hi [64]; ///< spreading factor for high-to-low threshold spreading in long frame
 }Psy3gppCoeffs;
 
 /**
  * Calculate Bark value for given line.
  */
 static inline float calc_bark(float f)
 {
     return 13.3f * atanf(0.00076f * f) + 3.5f * atanf((f / 7500.0f) * (f / 7500.0f));
 }