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float32.c：源码内容
							/*****************************************************************************
 * float32.c : precise float32 audio mixer implementation
 *****************************************************************************
 * Copyright (C) 2002 VideoLAN
 * $Id: float32.c 6961 2004-03-05 17:34:23Z sam $
 *
 * Authors: Christophe Massiot <massiot@via.ecp.fr>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
 *****************************************************************************/
/*****************************************************************************
 * Preamble
 *****************************************************************************/
#include <stdlib.h>                                      /* malloc(), free() */
#include <string.h>
#include <vlc/vlc.h>
#include "audio_output.h"
#include "aout_internal.h"
/*****************************************************************************
 * Local prototypes
 *****************************************************************************/
static int  Create    ( vlc_object_t * );
static void DoWork    ( aout_instance_t *, aout_buffer_t * );
/*****************************************************************************
 * Module descriptor
 *****************************************************************************/
vlc_module_begin();
    set_description( _("Float32 audio mixer") );
    set_capability( "audio mixer", 10 );
    set_callbacks( Create, NULL );
vlc_module_end();
/*****************************************************************************
 * Create: allocate mixer
 *****************************************************************************/
static int Create( vlc_object_t *p_this )
{
    aout_instance_t * p_aout = (aout_instance_t *)p_this;
    if ( p_aout->mixer.mixer.i_format != VLC_FOURCC('f','l','3','2') )
    {
        return -1;
    }
    if ( p_aout->i_nb_inputs == 1 && p_aout->mixer.f_multiplier == 1.0 )
    {
        /* Tell the trivial mixer to go for it. */
        return -1;
    }
    p_aout->mixer.pf_do_work = DoWork;
    return 0;
}
/*****************************************************************************
 * ScaleWords: prepare input words for averaging
 *****************************************************************************/
static void ScaleWords( float * p_out, const float * p_in, size_t i_nb_words,
                        int i_nb_inputs, float f_multiplier )
{
    int i;
    f_multiplier /= i_nb_inputs;
    for ( i = i_nb_words; i--; )
    {
        *p_out++ = *p_in++ * f_multiplier;
    }
}
/*****************************************************************************
 * MeanWords: average input words
 *****************************************************************************/
static void MeanWords( float * p_out, const float * p_in, size_t i_nb_words,
                       int i_nb_inputs, float f_multiplier )
{
    int i;
    f_multiplier /= i_nb_inputs;
    for ( i = i_nb_words; i--; )
    {
        *p_out++ += *p_in++ * f_multiplier;
    }
}
/*****************************************************************************
 * DoWork: mix a new output buffer
 *****************************************************************************
 * Terminology : in this function a word designates a single float32, eg.
 * a stereo sample is consituted of two words.
 *****************************************************************************/
static void DoWork( aout_instance_t * p_aout, aout_buffer_t * p_buffer )
{
    int i_nb_inputs = p_aout->i_nb_inputs;
    float f_multiplier = p_aout->mixer.f_multiplier;
    int i_input;
    int i_nb_channels = aout_FormatNbChannels( &p_aout->mixer.mixer );
    for ( i_input = 0; i_input < i_nb_inputs; i_input++ )
    {
        int i_nb_words = p_buffer->i_nb_samples * i_nb_channels;
        aout_input_t * p_input = p_aout->pp_inputs[i_input];
        float * p_out = (float *)p_buffer->p_buffer;
        float * p_in = (float *)p_input->p_first_byte_to_mix;
        if ( p_input->b_error ) continue;
        for ( ; ; )
        {
            ptrdiff_t i_available_words = (
                 (float *)p_input->fifo.p_first->p_buffer - p_in)
                                   + p_input->fifo.p_first->i_nb_samples
                                   * i_nb_channels;
            if ( i_available_words < i_nb_words )
            {
                aout_buffer_t * p_old_buffer;
                if ( i_available_words > 0 )
                {
                    if ( !i_input )
                    {
                        ScaleWords( p_out, p_in, i_available_words,
                                    i_nb_inputs, f_multiplier );
                    }
                    else
                    {
                        MeanWords( p_out, p_in, i_available_words,
                                   i_nb_inputs, f_multiplier );
                    }
                }
                i_nb_words -= i_available_words;
                p_out += i_available_words;
                /* Next buffer */
                p_old_buffer = aout_FifoPop( p_aout, &p_input->fifo );
                aout_BufferFree( p_old_buffer );
                if ( p_input->fifo.p_first == NULL )
                {
                    msg_Err( p_aout, "internal amix error" );
                    return;
                }
                p_in = (float *)p_input->fifo.p_first->p_buffer;
            }
            else
            {
                if ( i_nb_words > 0 )
                {
                    if ( !i_input )
                    {
                        ScaleWords( p_out, p_in, i_nb_words, i_nb_inputs,
                                    f_multiplier );
                    }
                    else
                    {
                        MeanWords( p_out, p_in, i_nb_words, i_nb_inputs,
                                   f_multiplier );
                    }
                }
                p_input->p_first_byte_to_mix = (void *)(p_in
                                            + i_nb_words);
                break;
            }
        }
    }
}

						