1 /*****************************************************************************
2 * fixed32tos16.c : converter from fixed32 to signed 16 bits integer
3 *****************************************************************************
4 * Copyright (C) 2002 VideoLAN
5 * $Id: fixed32tos16.c,v 1.4 2002/08/19 21:31:11 massiot Exp $
7 * Authors: Jean-Paul Saman <jpsaman@wxs.nl>
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License as published by
11 * the Free Software Foundation; either version 2 of the License, or
12 * (at your option) any later version.
14 * This program is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 * GNU General Public License for more details.
19 * You should have received a copy of the GNU General Public License
20 * along with this program; if not, write to the Free Software
21 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
22 *****************************************************************************/
24 /*****************************************************************************
26 *****************************************************************************/
28 #include <stdlib.h> /* malloc(), free() */
32 #include "audio_output.h"
33 #include "aout_internal.h"
35 /*****************************************************************************
37 *****************************************************************************/
38 static int Create ( vlc_object_t * );
40 static void DoWork ( aout_instance_t *, aout_filter_t *, aout_buffer_t *,
43 /*****************************************************************************
45 *****************************************************************************/
47 set_description( _("aout filter for fixed32->s16 conversion") );
48 set_capability( "audio filter", 10 );
49 set_callbacks( Create, NULL );
52 /*****************************************************************************
53 * Create: allocate trivial mixer
54 *****************************************************************************
55 * This function allocates and initializes a Crop vout method.
56 *****************************************************************************/
57 static int Create( vlc_object_t *p_this )
59 aout_filter_t * p_filter = (aout_filter_t *)p_this;
61 if ( p_filter->input.i_format != AOUT_FMT_FIXED32
62 || p_filter->output.i_format != AOUT_FMT_S16_NE )
67 if ( !AOUT_FMTS_SIMILAR( &p_filter->input, &p_filter->output ) )
72 p_filter->pf_do_work = DoWork;
73 p_filter->b_in_place = 1;
78 /*****************************************************************************
79 * support routines borrowed from mpg321 (file: mad.c), which is distributed
82 * mpg321 was written by Joe Drew <drew@debian.org>, and based upon 'plaympeg'
83 * from the smpeg sources, which was written by various people from Loki Software
84 * (http://www.lokigames.com).
86 * It also incorporates some source from mad, written by Robert Leslie
87 *****************************************************************************/
89 /* The following two routines and data structure are from the ever-brilliant
93 #define VLC_F_FRACBITS 28
95 # if VLC_F_FRACBITS == 28
96 # define VLC_F(x) ((vlc_fixed_t) (x##L))
99 # define VLC_F_ONE VLC_F(0x10000000)
101 struct audio_dither {
102 vlc_fixed_t error[3];
106 /********************************************************************
108 * DESCRIPTION: 32-bit pseudo-random number generator
109 ********************************************************************/
110 static inline unsigned long prng(unsigned long state)
112 return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL;
115 /********************************************************************
116 * NAME: mpg321_s24_to_s16_pcm()
117 * DESCRIPTION: generic linear sample quantize and dither routine
118 ********************************************************************/
119 static inline s16 mpg321_s24_to_s16_pcm(unsigned int bits, vlc_fixed_t sample,
120 struct audio_dither *dither)
122 unsigned int scalebits;
123 vlc_fixed_t output, mask, random;
131 sample += dither->error[0] - dither->error[1] + dither->error[2];
133 dither->error[2] = dither->error[1];
134 dither->error[1] = dither->error[0] / 2;
137 output = sample + (1L << (VLC_F_FRACBITS + 1 - bits - 1));
139 scalebits = VLC_F_FRACBITS + 1 - bits;
140 mask = (1L << scalebits) - 1;
143 random = prng(dither->random);
144 output += (random & mask) - (dither->random & mask);
146 dither->random = random;
155 else if (output < MIN) {
166 dither->error[0] = sample - output;
169 return output >> scalebits;
172 /*****************************************************************************
173 * s24_to_s16_pcm: Scale a 24 bit pcm sample to a 16 bit pcm sample.
174 *****************************************************************************/
175 static inline s16 s24_to_s16_pcm(vlc_fixed_t sample)
178 sample += (1L << (VLC_F_FRACBITS - 16));
181 if (sample >= VLC_F_ONE)
182 sample = VLC_F_ONE - 1;
183 else if (sample < -VLC_F_ONE)
187 return (sample >> (VLC_F_FRACBITS + 1 - 16));
190 /*****************************************************************************
191 * DoWork: convert a buffer
192 *****************************************************************************/
193 static void DoWork( aout_instance_t * p_aout, aout_filter_t * p_filter,
194 aout_buffer_t * p_in_buf, aout_buffer_t * p_out_buf )
197 vlc_fixed_t * p_in = (vlc_fixed_t *)p_in_buf->p_buffer;
198 s16 * p_out = (s16 *)p_out_buf->p_buffer;
200 // static struct audio_dither dither;
202 for ( i = p_in_buf->i_nb_samples * p_filter->input.i_channels ; i-- ; )
204 /* Accurate scaling */
205 // p_out = mpg321_s24_to_s16_pcm(16, *p_in++, &dither);
207 sample = s24_to_s16_pcm(*p_in++);
209 #ifndef WORDS_BIGENDIAN
210 *p_out++ = (s16) (sample >> 0);
211 *p_out++ = (s16) (sample >> 8);
213 *p_out++ = (s16) (sample >> 8);
214 *p_out++ = (s16) (sample >> 0);
218 p_out_buf->i_nb_samples = p_in_buf->i_nb_samples;