text: /*
   * The simplest AC-3 encoder
   * Copyright (c) 2000 Fabrice Bellard
   * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
   * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
   *
   * 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
   * fixed-point AC-3 encoder.
   */
  
  #define FFT_FLOAT 0
  #define AC3ENC_FLOAT 0
  #include "internal.h"
  #include "audiodsp.h"
  #include "ac3enc.h"
  #include "eac3enc.h"
  
  #define AC3ENC_TYPE AC3ENC_TYPE_AC3_FIXED
  #include "ac3enc_opts_template.c"
  
  static const AVClass ac3enc_class = {
      .class_name = "Fixed-Point AC-3 Encoder",
      .item_name  = av_default_item_name,
      .option     = ac3_options,
      .version    = LIBAVUTIL_VERSION_INT,
  };
  
  /*
   * Normalize the input samples to use the maximum available precision.
   * This assumes signed 16-bit input samples.
   */
  static int normalize_samples(AC3EncodeContext *s)
  {
      int v = s->ac3dsp.ac3_max_msb_abs_int16(s->windowed_samples, AC3_WINDOW_SIZE);
      v = 14 - av_log2(v);
      if (v > 0)
          s->ac3dsp.ac3_lshift_int16(s->windowed_samples, AC3_WINDOW_SIZE, v);
      /* +6 to right-shift from 31-bit to 25-bit */
      return v + 6;
  }
  
  
  /*
   * Scale MDCT coefficients to 25-bit signed fixed-point.
   */
  static void scale_coefficients(AC3EncodeContext *s)
  {
      int blk, ch;
  
      for (blk = 0; blk < s->num_blocks; blk++) {
          AC3Block *block = &s->blocks[blk];
          for (ch = 1; ch <= s->channels; ch++) {
              s->ac3dsp.ac3_rshift_int32(block->mdct_coef[ch], AC3_MAX_COEFS,
                                         block->coeff_shift[ch]);
          }
      }
  }
  
  static void sum_square_butterfly(AC3EncodeContext *s, int64_t sum[4],
                                   const int32_t *coef0, const int32_t *coef1,
                                   int len)
  {
      s->ac3dsp.sum_square_butterfly_int32(sum, coef0, coef1, len);
  }
  
  /*
   * Clip MDCT coefficients to allowable range.
   */
  static void clip_coefficients(AudioDSPContext *adsp, int32_t *coef,
                                unsigned int len)
  {
      adsp->vector_clip_int32(coef, coef, COEF_MIN, COEF_MAX, len);
  }
  
  
  /*
   * Calculate a single coupling coordinate.
   */
  static CoefType calc_cpl_coord(CoefSumType energy_ch, CoefSumType energy_cpl)
  {
      if (energy_cpl <= COEF_MAX) {
          return 1048576;
      } else {
          uint64_t coord   = energy_ch / (energy_cpl >> 24);
          uint32_t coord32 = FFMIN(coord, 1073741824);
          coord32          = ff_sqrt(coord32) << 9;
          return FFMIN(coord32, COEF_MAX);
      }
  }
  
  
  #include "ac3enc_template.c"
  
  
  /**
   * Finalize MDCT and free allocated memory.
   *
   * @param s  AC-3 encoder private context
   */
  static av_cold void ac3_fixed_mdct_end(AC3EncodeContext *s)
  {
      ff_mdct_end(&s->mdct);
  }
  
  
  /**
   * Initialize MDCT tables.
   *
   * @param s  AC-3 encoder private context
   * @return   0 on success, negative error code on failure
   */
  static av_cold int ac3_fixed_mdct_init(AC3EncodeContext *s)
  {
      int ret = ff_mdct_init(&s->mdct, 9, 0, -1.0);
      s->mdct_window = ff_ac3_window;
      return ret;
  }
  
  
  static av_cold int ac3_fixed_encode_init(AVCodecContext *avctx)
  {
      AC3EncodeContext *s = avctx->priv_data;
      s->fixed_point = 1;
      s->mdct_end                = ac3_fixed_mdct_end;
      s->mdct_init               = ac3_fixed_mdct_init;
      s->allocate_sample_buffers = allocate_sample_buffers;
      return ff_ac3_encode_init(avctx);
  }
  
  
  AVCodec ff_ac3_fixed_encoder = {
      .name            = "ac3_fixed",
      .long_name       = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
      .type            = AVMEDIA_TYPE_AUDIO,
      .id              = AV_CODEC_ID_AC3,
      .priv_data_size  = sizeof(AC3EncodeContext),
      .init            = ac3_fixed_encode_init,
      .encode2         = ff_ac3_fixed_encode_frame,
      .close           = ff_ac3_encode_close,
      .sample_fmts     = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_S16P,
                                                        AV_SAMPLE_FMT_NONE },
      .priv_class      = &ac3enc_class,
      .caps_internal   = FF_CODEC_CAP_INIT_THREADSAFE | FF_CODEC_CAP_INIT_CLEANUP,
      .supported_samplerates = ff_ac3_sample_rate_tab,
      .channel_layouts = ff_ac3_channel_layouts,
      .defaults        = ac3_defaults,
  };
  