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    1 /*
    2  * AAC encoder utilities
    3  * Copyright (C) 2015 Rostislav Pehlivanov
    4  *
    5  * This file is part of FFmpeg.
    6  *
    7  * FFmpeg is free software; you can redistribute it and/or
    8  * modify it under the terms of the GNU Lesser General Public
    9  * License as published by the Free Software Foundation; either
   10  * version 2.1 of the License, or (at your option) any later version.
   11  *
   12  * FFmpeg is distributed in the hope that it will be useful,
   13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   15  * Lesser General Public License for more details.
   16  *
   17  * You should have received a copy of the GNU Lesser General Public
   18  * License along with FFmpeg; if not, write to the Free Software
   19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   20  */
   21 
   22 /**
   23  * @file
   24  * AAC encoder utilities
   25  * @author Rostislav Pehlivanov ( atomnuker gmail com )
   26  */
   27 
   28 #ifndef AVCODEC_AACENC_UTILS_H
   29 #define AVCODEC_AACENC_UTILS_H
   30 
   31 #include "libavutil/ffmath.h"
   32 #include "aac.h"
   33 #include "aacenctab.h"
   34 #include "aactab.h"
   35 
   36 #define ROUND_STANDARD 0.4054f
   37 #define ROUND_TO_ZERO 0.1054f
   38 #define C_QUANT 0.4054f
   39 
   40 static inline void abs_pow34_v(float *out, const float *in, const int size)
   41 {
   42     int i;
   43     for (i = 0; i < size; i++) {
   44         float a = fabsf(in[i]);
   45         out[i] = sqrtf(a * sqrtf(a));
   46     }
   47 }
   48 
   49 static inline float pos_pow34(float a)
   50 {
   51     return sqrtf(a * sqrtf(a));
   52 }
   53 
   54 /**
   55  * Quantize one coefficient.
   56  * @return absolute value of the quantized coefficient
   57  * @see 3GPP TS26.403 5.6.2 "Scalefactor determination"
   58  */
   59 static inline int quant(float coef, const float Q, const float rounding)
   60 {
   61     float a = coef * Q;
   62     return sqrtf(a * sqrtf(a)) + rounding;
   63 }
   64 
   65 static inline void quantize_bands(int *out, const float *in, const float *scaled,
   66                                   int size, int is_signed, int maxval, const float Q34,
   67                                   const float rounding)
   68 {
   69     int i;
   70     for (i = 0; i < size; i++) {
   71         float qc = scaled[i] * Q34;
   72         int tmp = (int)FFMIN(qc + rounding, (float)maxval);
   73         if (is_signed && in[i] < 0.0f) {
   74             tmp = -tmp;
   75         }
   76         out[i] = tmp;
   77     }
   78 }
   79 
   80 static inline float find_max_val(int group_len, int swb_size, const float *scaled)
   81 {
   82     float maxval = 0.0f;
   83     int w2, i;
   84     for (w2 = 0; w2 < group_len; w2++) {
   85         for (i = 0; i < swb_size; i++) {
   86             maxval = FFMAX(maxval, scaled[w2*128+i]);
   87         }
   88     }
   89     return maxval;
   90 }
   91 
   92 static inline int find_min_book(float maxval, int sf)
   93 {
   94     float Q34 = ff_aac_pow34sf_tab[POW_SF2_ZERO - sf + SCALE_ONE_POS - SCALE_DIV_512];
   95     int qmaxval, cb;
   96     qmaxval = maxval * Q34 + C_QUANT;
   97     if (qmaxval >= (FF_ARRAY_ELEMS(aac_maxval_cb)))
   98         cb = 11;
   99     else
  100         cb = aac_maxval_cb[qmaxval];
  101     return cb;
  102 }
  103 
  104 static inline float find_form_factor(int group_len, int swb_size, float thresh,
  105                                      const float *scaled, float nzslope) {
  106     const float iswb_size = 1.0f / swb_size;
  107     const float iswb_sizem1 = 1.0f / (swb_size - 1);
  108     const float ethresh = thresh;
  109     float form = 0.0f, weight = 0.0f;
  110     int w2, i;
  111     for (w2 = 0; w2 < group_len; w2++) {
  112         float e = 0.0f, e2 = 0.0f, var = 0.0f, maxval = 0.0f;
  113         float nzl = 0;
  114         for (i = 0; i < swb_size; i++) {
  115             float s = fabsf(scaled[w2*128+i]);
  116             maxval = FFMAX(maxval, s);
  117             e += s;
  118             e2 += s *= s;
  119             /* We really don't want a hard non-zero-line count, since
  120              * even below-threshold lines do add up towards band spectral power.
  121              * So, fall steeply towards zero, but smoothly
  122              */
  123             if (s >= ethresh) {
  124                 nzl += 1.0f;
  125             } else {
  126                 if (nzslope == 2.f)
  127                     nzl += (s / ethresh) * (s / ethresh);
  128                 else
  129                     nzl += ff_fast_powf(s / ethresh, nzslope);
  130             }
  131         }
  132         if (e2 > thresh) {
  133             float frm;
  134             e *= iswb_size;
  135 
  136             /** compute variance */
  137             for (i = 0; i < swb_size; i++) {
  138                 float d = fabsf(scaled[w2*128+i]) - e;
  139                 var += d*d;
  140             }
  141             var = sqrtf(var * iswb_sizem1);
  142 
  143             e2 *= iswb_size;
  144             frm = e / FFMIN(e+4*var,maxval);
  145             form += e2 * sqrtf(frm) / FFMAX(0.5f,nzl);
  146             weight += e2;
  147         }
  148     }
  149     if (weight > 0) {
  150         return form / weight;
  151     } else {
  152         return 1.0f;
  153     }
  154 }
  155 
  156 /** Return the minimum scalefactor where the quantized coef does not clip. */
  157 static inline uint8_t coef2minsf(float coef)
  158 {
  159     return av_clip_uint8(log2f(coef)*4 - 69 + SCALE_ONE_POS - SCALE_DIV_512);
  160 }
  161 
  162 /** Return the maximum scalefactor where the quantized coef is not zero. */
  163 static inline uint8_t coef2maxsf(float coef)
  164 {
  165     return av_clip_uint8(log2f(coef)*4 +  6 + SCALE_ONE_POS - SCALE_DIV_512);
  166 }
  167 
  168 /*
  169  * Returns the closest possible index to an array of float values, given a value.
  170  */
  171 static inline int quant_array_idx(const float val, const float *arr, const int num)
  172 {
  173     int i, index = 0;
  174     float quant_min_err = INFINITY;
  175     for (i = 0; i < num; i++) {
  176         float error = (val - arr[i])*(val - arr[i]);
  177         if (error < quant_min_err) {
  178             quant_min_err = error;
  179             index = i;
  180         }
  181     }
  182     return index;
  183 }
  184 
  185 /**
  186  * approximates exp10f(-3.0f*(0.5f + 0.5f * cosf(FFMIN(b,15.5f) / 15.5f)))
  187  */
  188 static av_always_inline float bval2bmax(float b)
  189 {
  190     return 0.001f + 0.0035f * (b*b*b) / (15.5f*15.5f*15.5f);
  191 }
  192 
  193 /*
  194  * Compute a nextband map to be used with SF delta constraint utilities.
  195  * The nextband array should contain 128 elements, and positions that don't
  196  * map to valid, nonzero bands of the form w*16+g (with w being the initial
  197  * window of the window group, only) are left indetermined.
  198  */
  199 static inline void ff_init_nextband_map(const SingleChannelElement *sce, uint8_t *nextband)
  200 {
  201     unsigned char prevband = 0;
  202     int w, g;
  203     /** Just a safe default */
  204     for (g = 0; g < 128; g++)
  205         nextband[g] = g;
  206 
  207     /** Now really navigate the nonzero band chain */
  208     for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
  209         for (g = 0; g < sce->ics.num_swb; g++) {
  210             if (!sce->zeroes[w*16+g] && sce->band_type[w*16+g] < RESERVED_BT)
  211                 prevband = nextband[prevband] = w*16+g;
  212         }
  213     }
  214     nextband[prevband] = prevband; /* terminate */
  215 }
  216 
  217 /*
  218  * Updates nextband to reflect a removed band (equivalent to
  219  * calling ff_init_nextband_map after marking a band as zero)
  220  */
  221 static inline void ff_nextband_remove(uint8_t *nextband, int prevband, int band)
  222 {
  223     nextband[prevband] = nextband[band];
  224 }
  225 
  226 /*
  227  * Checks whether the specified band could be removed without inducing
  228  * scalefactor delta that violates SF delta encoding constraints.
  229  * prev_sf has to be the scalefactor of the previous nonzero, nonspecial
  230  * band, in encoding order, or negative if there was no such band.
  231  */
  232 static inline int ff_sfdelta_can_remove_band(const SingleChannelElement *sce,
  233     const uint8_t *nextband, int prev_sf, int band)
  234 {
  235     return prev_sf >= 0
  236         && sce->sf_idx[nextband[band]] >= (prev_sf - SCALE_MAX_DIFF)
  237         && sce->sf_idx[nextband[band]] <= (prev_sf + SCALE_MAX_DIFF);
  238 }
  239 
  240 /*
  241  * Checks whether the specified band's scalefactor could be replaced
  242  * with another one without violating SF delta encoding constraints.
  243  * prev_sf has to be the scalefactor of the previous nonzero, nonsepcial
  244  * band, in encoding order, or negative if there was no such band.
  245  */
  246 static inline int ff_sfdelta_can_replace(const SingleChannelElement *sce,
  247     const uint8_t *nextband, int prev_sf, int new_sf, int band)
  248 {
  249     return new_sf >= (prev_sf - SCALE_MAX_DIFF)
  250         && new_sf <= (prev_sf + SCALE_MAX_DIFF)
  251         && sce->sf_idx[nextband[band]] >= (new_sf - SCALE_MAX_DIFF)
  252         && sce->sf_idx[nextband[band]] <= (new_sf + SCALE_MAX_DIFF);
  253 }
  254 
  255 /**
  256  * linear congruential pseudorandom number generator
  257  *
  258  * @param   previous_val    pointer to the current state of the generator
  259  *
  260  * @return  Returns a 32-bit pseudorandom integer
  261  */
  262 static av_always_inline int lcg_random(unsigned previous_val)
  263 {
  264     union { unsigned u; int s; } v = { previous_val * 1664525u + 1013904223 };
  265     return v.s;
  266 }
  267 
  268 #define ERROR_IF(cond, ...) \
  269     if (cond) { \
  270         av_log(avctx, AV_LOG_ERROR, __VA_ARGS__); \
  271         return AVERROR(EINVAL); \
  272     }
  273 
  274 #define WARN_IF(cond, ...) \
  275     if (cond) { \
  276         av_log(avctx, AV_LOG_WARNING, __VA_ARGS__); \
  277     }
  278 
  279 #endif /* AVCODEC_AACENC_UTILS_H */