/src/opus/silk/stereo_LR_to_MS.c

Source
/***********************************************************************
Copyright (c) 2006-2011, Skype Limited. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
- Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
- Neither the name of Internet Society, IETF or IETF Trust, nor the
names of specific contributors, may be used to endorse or promote
products derived from this software without specific prior written
permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
***********************************************************************/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "main.h"
#include "stack_alloc.h"

/* Convert Left/Right stereo signal to adaptive Mid/Side representation */
void silk_stereo_LR_to_MS(
    stereo_enc_state            *state,                         /* I/O  State                                       */
    opus_int16                  x1[],                           /* I/O  Left input signal, becomes mid signal       */
    opus_int16                  x2[],                           /* I/O  Right input signal, becomes side signal     */
    opus_int8                   ix[ 2 ][ 3 ],                   /* O    Quantization indices                        */
    opus_int8                   *mid_only_flag,                 /* O    Flag: only mid signal coded                 */
    opus_int32                  mid_side_rates_bps[],           /* O    Bitrates for mid and side signals           */
    opus_int32                  total_rate_bps,                 /* I    Total bitrate                               */
    opus_int                    prev_speech_act_Q8,             /* I    Speech activity level in previous frame     */
    opus_int                    toMono,                         /* I    Last frame before a stereo->mono transition */
    opus_int                    fs_kHz,                         /* I    Sample rate (kHz)                           */
    opus_int                    frame_length                    /* I    Number of samples                           */
)
{
    opus_int   n, is10msFrame, denom_Q16, delta0_Q13, delta1_Q13;
    opus_int32 sum, diff, smooth_coef_Q16, pred_Q13[ 2 ], pred0_Q13, pred1_Q13;
    opus_int32 LP_ratio_Q14, HP_ratio_Q14, frac_Q16, frac_3_Q16, min_mid_rate_bps, width_Q14, w_Q24, deltaw_Q24;
    VARDECL( opus_int16, side );
    VARDECL( opus_int16, LP_mid );
    VARDECL( opus_int16, HP_mid );
    VARDECL( opus_int16, LP_side );
    VARDECL( opus_int16, HP_side );
    opus_int16 *mid = &x1[ -2 ];
    SAVE_STACK;

    ALLOC( side, frame_length + 2, opus_int16 );
    /* Convert to basic mid/side signals */
    for( n = 0; n < frame_length + 2; n++ ) {
        sum  = x1[ n - 2 ] + (opus_int32)x2[ n - 2 ];
        diff = x1[ n - 2 ] - (opus_int32)x2[ n - 2 ];
        mid[  n ] = (opus_int16)silk_RSHIFT_ROUND( sum, 1 );
        side[ n ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( diff, 1 ) );
    }

    /* Buffering */
    silk_memcpy( mid,  state->sMid,  2 * sizeof( opus_int16 ) );
    silk_memcpy( side, state->sSide, 2 * sizeof( opus_int16 ) );
    silk_memcpy( state->sMid,  &mid[  frame_length ], 2 * sizeof( opus_int16 ) );
    silk_memcpy( state->sSide, &side[ frame_length ], 2 * sizeof( opus_int16 ) );

    /* LP and HP filter mid signal */
    ALLOC( LP_mid, frame_length, opus_int16 );
    ALLOC( HP_mid, frame_length, opus_int16 );
    for( n = 0; n < frame_length; n++ ) {
        sum = silk_RSHIFT_ROUND( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 2 );
        LP_mid[ n ] = sum;
        HP_mid[ n ] = mid[ n + 1 ] - sum;
    }

    /* LP and HP filter side signal */
    ALLOC( LP_side, frame_length, opus_int16 );
    ALLOC( HP_side, frame_length, opus_int16 );
    for( n = 0; n < frame_length; n++ ) {
        sum = silk_RSHIFT_ROUND( silk_ADD_LSHIFT32( side[ n ] + (opus_int32)side[ n + 2 ], side[ n + 1 ], 1 ), 2 );
        LP_side[ n ] = sum;
        HP_side[ n ] = side[ n + 1 ] - sum;
    }

    /* Find energies and predictors */
    is10msFrame = frame_length == 10 * fs_kHz;
    smooth_coef_Q16 = is10msFrame ?
        SILK_FIX_CONST( STEREO_RATIO_SMOOTH_COEF / 2, 16 ) :
        SILK_FIX_CONST( STEREO_RATIO_SMOOTH_COEF,     16 );
    smooth_coef_Q16 = silk_SMULWB( silk_SMULBB( prev_speech_act_Q8, prev_speech_act_Q8 ), smooth_coef_Q16 );

    pred_Q13[ 0 ] = silk_stereo_find_predictor( &LP_ratio_Q14, LP_mid, LP_side, &state->mid_side_amp_Q0[ 0 ], frame_length, smooth_coef_Q16 );
    pred_Q13[ 1 ] = silk_stereo_find_predictor( &HP_ratio_Q14, HP_mid, HP_side, &state->mid_side_amp_Q0[ 2 ], frame_length, smooth_coef_Q16 );
    /* Ratio of the norms of residual and mid signals */
    frac_Q16 = silk_SMLABB( HP_ratio_Q14, LP_ratio_Q14, 3 );
    frac_Q16 = silk_min( frac_Q16, SILK_FIX_CONST( 1, 16 ) );

    /* Determine bitrate distribution between mid and side, and possibly reduce stereo width */
    total_rate_bps -= is10msFrame ? 1200 : 600;      /* Subtract approximate bitrate for coding stereo parameters */
    if( total_rate_bps < 1 ) {
        total_rate_bps = 1;
    }
    min_mid_rate_bps = silk_SMLABB( 2000, fs_kHz, 600 );
    silk_assert( min_mid_rate_bps < 32767 );
    /* Default bitrate distribution: 8 parts for Mid and (5+3*frac) parts for Side. so: mid_rate = ( 8 / ( 13 + 3 * frac ) ) * total_ rate */
    frac_3_Q16 = silk_MUL( 3, frac_Q16 );
    mid_side_rates_bps[ 0 ] = silk_DIV32_varQ( total_rate_bps, SILK_FIX_CONST( 8 + 5, 16 ) + frac_3_Q16, 16+3 );
    /* If Mid bitrate below minimum, reduce stereo width */
    if( mid_side_rates_bps[ 0 ] < min_mid_rate_bps ) {
        mid_side_rates_bps[ 0 ] = min_mid_rate_bps;
        mid_side_rates_bps[ 1 ] = total_rate_bps - mid_side_rates_bps[ 0 ];
        /* width = 4 * ( 2 * side_rate - min_rate ) / ( ( 1 + 3 * frac ) * min_rate ) */
        width_Q14 = silk_DIV32_varQ( silk_LSHIFT( mid_side_rates_bps[ 1 ], 1 ) - min_mid_rate_bps,
            silk_SMULWB( SILK_FIX_CONST( 1, 16 ) + frac_3_Q16, min_mid_rate_bps ), 14+2 );
        width_Q14 = silk_LIMIT( width_Q14, 0, SILK_FIX_CONST( 1, 14 ) );
    } else {
        mid_side_rates_bps[ 1 ] = total_rate_bps - mid_side_rates_bps[ 0 ];
        width_Q14 = SILK_FIX_CONST( 1, 14 );
    }

    /* Smoother */
    state->smth_width_Q14 = (opus_int16)silk_SMLAWB( state->smth_width_Q14, width_Q14 - state->smth_width_Q14, smooth_coef_Q16 );

    /* At very low bitrates or for inputs that are nearly amplitude panned, switch to panned-mono coding */
    *mid_only_flag = 0;
    if( toMono ) {
        /* Last frame before stereo->mono transition; collapse stereo width */
        width_Q14 = 0;
        pred_Q13[ 0 ] = 0;
        pred_Q13[ 1 ] = 0;
        silk_stereo_quant_pred( pred_Q13, ix );
    } else if( state->width_prev_Q14 == 0 &&
        ( 8 * total_rate_bps < 13 * min_mid_rate_bps || silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.05, 14 ) ) )
    {
        /* Code as panned-mono; previous frame already had zero width */
        /* Scale down and quantize predictors */
        pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
        pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
        silk_stereo_quant_pred( pred_Q13, ix );
        /* Collapse stereo width */
        width_Q14 = 0;
        pred_Q13[ 0 ] = 0;
        pred_Q13[ 1 ] = 0;
        mid_side_rates_bps[ 0 ] = total_rate_bps;
        mid_side_rates_bps[ 1 ] = 0;
        *mid_only_flag = 1;
    } else if( state->width_prev_Q14 != 0 &&
        ( 8 * total_rate_bps < 11 * min_mid_rate_bps || silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.02, 14 ) ) )
    {
        /* Transition to zero-width stereo */
        /* Scale down and quantize predictors */
        pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
        pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
        silk_stereo_quant_pred( pred_Q13, ix );
        /* Collapse stereo width */
        width_Q14 = 0;
        pred_Q13[ 0 ] = 0;
        pred_Q13[ 1 ] = 0;
    } else if( state->smth_width_Q14 > SILK_FIX_CONST( 0.95, 14 ) ) {
        /* Full-width stereo coding */
        silk_stereo_quant_pred( pred_Q13, ix );
        width_Q14 = SILK_FIX_CONST( 1, 14 );
    } else {
        /* Reduced-width stereo coding; scale down and quantize predictors */
        pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
        pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
        silk_stereo_quant_pred( pred_Q13, ix );
        width_Q14 = state->smth_width_Q14;
    }

    /* Make sure to keep on encoding until the tapered output has been transmitted */
    if( *mid_only_flag == 1 ) {
        state->silent_side_len += frame_length - STEREO_INTERP_LEN_MS * fs_kHz;
        if( state->silent_side_len < LA_SHAPE_MS * fs_kHz ) {
            *mid_only_flag = 0;
        } else {
            /* Limit to avoid wrapping around */
            state->silent_side_len = 10000;
        }
    } else {
        state->silent_side_len = 0;
    }

    if( *mid_only_flag == 0 && mid_side_rates_bps[ 1 ] < 1 ) {
        mid_side_rates_bps[ 1 ] = 1;
        mid_side_rates_bps[ 0 ] = silk_max_int( 1, total_rate_bps - mid_side_rates_bps[ 1 ]);
    }

    /* Interpolate predictors and subtract prediction from side channel */
    pred0_Q13  = -state->pred_prev_Q13[ 0 ];
    pred1_Q13  = -state->pred_prev_Q13[ 1 ];
    w_Q24      =  silk_LSHIFT( state->width_prev_Q14, 10 );
    denom_Q16  = silk_DIV32_16( (opus_int32)1 << 16, STEREO_INTERP_LEN_MS * fs_kHz );
    delta0_Q13 = -silk_RSHIFT_ROUND( silk_SMULBB( pred_Q13[ 0 ] - state->pred_prev_Q13[ 0 ], denom_Q16 ), 16 );
    delta1_Q13 = -silk_RSHIFT_ROUND( silk_SMULBB( pred_Q13[ 1 ] - state->pred_prev_Q13[ 1 ], denom_Q16 ), 16 );
    deltaw_Q24 =  silk_LSHIFT( silk_SMULWB( width_Q14 - state->width_prev_Q14, denom_Q16 ), 10 );
    for( n = 0; n < STEREO_INTERP_LEN_MS * fs_kHz; n++ ) {
        pred0_Q13 += delta0_Q13;
        pred1_Q13 += delta1_Q13;
        w_Q24   += deltaw_Q24;
        sum = silk_LSHIFT( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 9 );    /* Q11 */
        sum = silk_SMLAWB( silk_SMULWB( w_Q24, side[ n + 1 ] ), sum, pred0_Q13 );               /* Q8  */
        sum = silk_SMLAWB( sum, silk_LSHIFT( (opus_int32)mid[ n + 1 ], 11 ), pred1_Q13 );       /* Q8  */
        x2[ n - 1 ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( sum, 8 ) );
    }

    pred0_Q13 = -pred_Q13[ 0 ];
    pred1_Q13 = -pred_Q13[ 1 ];
    w_Q24     =  silk_LSHIFT( width_Q14, 10 );
    for( n = STEREO_INTERP_LEN_MS * fs_kHz; n < frame_length; n++ ) {
        sum = silk_LSHIFT( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 9 );    /* Q11 */
        sum = silk_SMLAWB( silk_SMULWB( w_Q24, side[ n + 1 ] ), sum, pred0_Q13 );               /* Q8  */
        sum = silk_SMLAWB( sum, silk_LSHIFT( (opus_int32)mid[ n + 1 ], 11 ), pred1_Q13 );       /* Q8  */
        x2[ n - 1 ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( sum, 8 ) );
    }
    state->pred_prev_Q13[ 0 ] = (opus_int16)pred_Q13[ 0 ];
    state->pred_prev_Q13[ 1 ] = (opus_int16)pred_Q13[ 1 ];
    state->width_prev_Q14     = (opus_int16)width_Q14;
    RESTORE_STACK;
}

Coverage Report

Created: 2025-11-11 07:47

Line	Count	Source
1		/***********************************************************************
2		Copyright (c) 2006-2011, Skype Limited. All rights reserved.
3		Redistribution and use in source and binary forms, with or without
4		modification, are permitted provided that the following conditions
5		are met:
6		- Redistributions of source code must retain the above copyright notice,
7		this list of conditions and the following disclaimer.
8		- Redistributions in binary form must reproduce the above copyright
9		notice, this list of conditions and the following disclaimer in the
10		documentation and/or other materials provided with the distribution.
11		- Neither the name of Internet Society, IETF or IETF Trust, nor the
12		names of specific contributors, may be used to endorse or promote
13		products derived from this software without specific prior written
14		permission.
15		THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
16		AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17		IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18		ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
19		LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
20		CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
21		SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
22		INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
23		CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
24		ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
25		POSSIBILITY OF SUCH DAMAGE.
26		***********************************************************************/
27
28		#ifdef HAVE_CONFIG_H
29		#include "config.h"
30		#endif
31
32		#include "main.h"
33		#include "stack_alloc.h"
34
35		/* Convert Left/Right stereo signal to adaptive Mid/Side representation */
36		void silk_stereo_LR_to_MS(
37		stereo_enc_state state, / I/O State */
38		opus_int16 x1[], /* I/O Left input signal, becomes mid signal */
39		opus_int16 x2[], /* I/O Right input signal, becomes side signal */
40		opus_int8 ix[ 2 ][ 3 ], /* O Quantization indices */
41		opus_int8 mid_only_flag, / O Flag: only mid signal coded */
42		opus_int32 mid_side_rates_bps[], /* O Bitrates for mid and side signals */
43		opus_int32 total_rate_bps, /* I Total bitrate */
44		opus_int prev_speech_act_Q8, /* I Speech activity level in previous frame */
45		opus_int toMono, /* I Last frame before a stereo->mono transition */
46		opus_int fs_kHz, /* I Sample rate (kHz) */
47		opus_int frame_length /* I Number of samples */
48		)
49	13.0M	{
50	13.0M	opus_int n, is10msFrame, denom_Q16, delta0_Q13, delta1_Q13;
51	13.0M	opus_int32 sum, diff, smooth_coef_Q16, pred_Q13[ 2 ], pred0_Q13, pred1_Q13;
52	13.0M	opus_int32 LP_ratio_Q14, HP_ratio_Q14, frac_Q16, frac_3_Q16, min_mid_rate_bps, width_Q14, w_Q24, deltaw_Q24;
53	13.0M	VARDECL( opus_int16, side );
54	13.0M	VARDECL( opus_int16, LP_mid );
55	13.0M	VARDECL( opus_int16, HP_mid );
56	13.0M	VARDECL( opus_int16, LP_side );
57	13.0M	VARDECL( opus_int16, HP_side );
58	13.0M	opus_int16 *mid = &x1[ -2 ];
59	13.0M	SAVE_STACK;
60
61	13.0M	ALLOC( side, frame_length + 2, opus_int16 );
62		/* Convert to basic mid/side signals */
63	2.28G	for( n = 0; n < frame_length + 2; n++ ) {
64	2.27G	sum = x1[ n - 2 ] + (opus_int32)x2[ n - 2 ];
65	2.27G	diff = x1[ n - 2 ] - (opus_int32)x2[ n - 2 ];
66	2.27G	mid[ n ] = (opus_int16)silk_RSHIFT_ROUND( sum, 1 );
67	2.27G	side[ n ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( diff, 1 ) );
68	2.27G	}
69
70		/* Buffering */
71	13.0M	silk_memcpy( mid, state->sMid, 2 * sizeof( opus_int16 ) );
72	13.0M	silk_memcpy( side, state->sSide, 2 * sizeof( opus_int16 ) );
73	13.0M	silk_memcpy( state->sMid, &mid[ frame_length ], 2 * sizeof( opus_int16 ) );
74	13.0M	silk_memcpy( state->sSide, &side[ frame_length ], 2 * sizeof( opus_int16 ) );
75
76		/* LP and HP filter mid signal */
77	13.0M	ALLOC( LP_mid, frame_length, opus_int16 );
78	13.0M	ALLOC( HP_mid, frame_length, opus_int16 );
79	2.25G	for( n = 0; n < frame_length; n++ ) {
80	2.24G	sum = silk_RSHIFT_ROUND( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 2 );
81	2.24G	LP_mid[ n ] = sum;
82	2.24G	HP_mid[ n ] = mid[ n + 1 ] - sum;
83	2.24G	}
84
85		/* LP and HP filter side signal */
86	13.0M	ALLOC( LP_side, frame_length, opus_int16 );
87	13.0M	ALLOC( HP_side, frame_length, opus_int16 );
88	2.25G	for( n = 0; n < frame_length; n++ ) {
89	2.24G	sum = silk_RSHIFT_ROUND( silk_ADD_LSHIFT32( side[ n ] + (opus_int32)side[ n + 2 ], side[ n + 1 ], 1 ), 2 );
90	2.24G	LP_side[ n ] = sum;
91	2.24G	HP_side[ n ] = side[ n + 1 ] - sum;
92	2.24G	}
93
94		/* Find energies and predictors */
95	13.0M	is10msFrame = frame_length == 10 * fs_kHz;
96	13.0M	smooth_coef_Q16 = is10msFrame ?
97	5.44M	SILK_FIX_CONST( STEREO_RATIO_SMOOTH_COEF / 2, 16 ) :
98	13.0M	SILK_FIX_CONST( STEREO_RATIO_SMOOTH_COEF, 16 );
99	13.0M	smooth_coef_Q16 = silk_SMULWB( silk_SMULBB( prev_speech_act_Q8, prev_speech_act_Q8 ), smooth_coef_Q16 );
100
101	13.0M	pred_Q13[ 0 ] = silk_stereo_find_predictor( &LP_ratio_Q14, LP_mid, LP_side, &state->mid_side_amp_Q0[ 0 ], frame_length, smooth_coef_Q16 );
102	13.0M	pred_Q13[ 1 ] = silk_stereo_find_predictor( &HP_ratio_Q14, HP_mid, HP_side, &state->mid_side_amp_Q0[ 2 ], frame_length, smooth_coef_Q16 );
103		/* Ratio of the norms of residual and mid signals */
104	13.0M	frac_Q16 = silk_SMLABB( HP_ratio_Q14, LP_ratio_Q14, 3 );
105	13.0M	frac_Q16 = silk_min( frac_Q16, SILK_FIX_CONST( 1, 16 ) );
106
107		/* Determine bitrate distribution between mid and side, and possibly reduce stereo width */
108	13.0M	total_rate_bps -= is10msFrame ? 1200 : 600; /* Subtract approximate bitrate for coding stereo parameters */
109	13.0M	if( total_rate_bps < 1 ) {
110	0	total_rate_bps = 1;
111	0	}
112	13.0M	min_mid_rate_bps = silk_SMLABB( 2000, fs_kHz, 600 );
113	13.0M	silk_assert( min_mid_rate_bps < 32767 );
114		/* Default bitrate distribution: 8 parts for Mid and (5+3frac) parts for Side. so: mid_rate = ( 8 / ( 13 + 3 frac ) ) * total_ rate */
115	13.0M	frac_3_Q16 = silk_MUL( 3, frac_Q16 );
116	13.0M	mid_side_rates_bps[ 0 ] = silk_DIV32_varQ( total_rate_bps, SILK_FIX_CONST( 8 + 5, 16 ) + frac_3_Q16, 16+3 );
117		/* If Mid bitrate below minimum, reduce stereo width */
118	13.0M	if( mid_side_rates_bps[ 0 ] < min_mid_rate_bps ) {
119	94.0k	mid_side_rates_bps[ 0 ] = min_mid_rate_bps;
120	94.0k	mid_side_rates_bps[ 1 ] = total_rate_bps - mid_side_rates_bps[ 0 ];
121		/* width = 4 * ( 2 * side_rate - min_rate ) / ( ( 1 + 3 * frac ) * min_rate ) */
122	94.0k	width_Q14 = silk_DIV32_varQ( silk_LSHIFT( mid_side_rates_bps[ 1 ], 1 ) - min_mid_rate_bps,
123	94.0k	silk_SMULWB( SILK_FIX_CONST( 1, 16 ) + frac_3_Q16, min_mid_rate_bps ), 14+2 );
124	94.0k	width_Q14 = silk_LIMIT( width_Q14, 0, SILK_FIX_CONST( 1, 14 ) );
125	13.0M	} else {
126	13.0M	mid_side_rates_bps[ 1 ] = total_rate_bps - mid_side_rates_bps[ 0 ];
127	13.0M	width_Q14 = SILK_FIX_CONST( 1, 14 );
128	13.0M	}
129
130		/* Smoother */
131	13.0M	state->smth_width_Q14 = (opus_int16)silk_SMLAWB( state->smth_width_Q14, width_Q14 - state->smth_width_Q14, smooth_coef_Q16 );
132
133		/* At very low bitrates or for inputs that are nearly amplitude panned, switch to panned-mono coding */
134	13.0M	*mid_only_flag = 0;
135	13.0M	if( toMono ) {
136		/* Last frame before stereo->mono transition; collapse stereo width */
137	0	width_Q14 = 0;
138	0	pred_Q13[ 0 ] = 0;
139	0	pred_Q13[ 1 ] = 0;
140	0	silk_stereo_quant_pred( pred_Q13, ix );
141	13.0M	} else if( state->width_prev_Q14 == 0 &&
142	2.96M	( 8 * total_rate_bps < 13 * min_mid_rate_bps \|\| silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.05, 14 ) ) )
143	2.90M	{
144		/* Code as panned-mono; previous frame already had zero width */
145		/* Scale down and quantize predictors */
146	2.90M	pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
147	2.90M	pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
148	2.90M	silk_stereo_quant_pred( pred_Q13, ix );
149		/* Collapse stereo width */
150	2.90M	width_Q14 = 0;
151	2.90M	pred_Q13[ 0 ] = 0;
152	2.90M	pred_Q13[ 1 ] = 0;
153	2.90M	mid_side_rates_bps[ 0 ] = total_rate_bps;
154	2.90M	mid_side_rates_bps[ 1 ] = 0;
155	2.90M	*mid_only_flag = 1;
156	10.1M	} else if( state->width_prev_Q14 != 0 &&
157	10.1M	( 8 * total_rate_bps < 11 * min_mid_rate_bps \|\| silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.02, 14 ) ) )
158	10.7k	{
159		/* Transition to zero-width stereo */
160		/* Scale down and quantize predictors */
161	10.7k	pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
162	10.7k	pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
163	10.7k	silk_stereo_quant_pred( pred_Q13, ix );
164		/* Collapse stereo width */
165	10.7k	width_Q14 = 0;
166	10.7k	pred_Q13[ 0 ] = 0;
167	10.7k	pred_Q13[ 1 ] = 0;
168	10.1M	} else if( state->smth_width_Q14 > SILK_FIX_CONST( 0.95, 14 ) ) {
169		/* Full-width stereo coding */
170	9.21M	silk_stereo_quant_pred( pred_Q13, ix );
171	9.21M	width_Q14 = SILK_FIX_CONST( 1, 14 );
172	9.21M	} else {
173		/* Reduced-width stereo coding; scale down and quantize predictors */
174	964k	pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
175	964k	pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
176	964k	silk_stereo_quant_pred( pred_Q13, ix );
177	964k	width_Q14 = state->smth_width_Q14;
178	964k	}
179
180		/* Make sure to keep on encoding until the tapered output has been transmitted */
181	13.0M	if( *mid_only_flag == 1 ) {
182	2.90M	state->silent_side_len += frame_length - STEREO_INTERP_LEN_MS * fs_kHz;
183	2.90M	if( state->silent_side_len < LA_SHAPE_MS * fs_kHz ) {
184	3.98k	*mid_only_flag = 0;
185	2.90M	} else {
186		/* Limit to avoid wrapping around */
187	2.90M	state->silent_side_len = 10000;
188	2.90M	}
189	10.1M	} else {
190	10.1M	state->silent_side_len = 0;
191	10.1M	}
192
193	13.0M	if( *mid_only_flag == 0 && mid_side_rates_bps[ 1 ] < 1 ) {
194	9.69k	mid_side_rates_bps[ 1 ] = 1;
195	9.69k	mid_side_rates_bps[ 0 ] = silk_max_int( 1, total_rate_bps - mid_side_rates_bps[ 1 ]);
196	9.69k	}
197
198		/* Interpolate predictors and subtract prediction from side channel */
199	13.0M	pred0_Q13 = -state->pred_prev_Q13[ 0 ];
200	13.0M	pred1_Q13 = -state->pred_prev_Q13[ 1 ];
201	13.0M	w_Q24 = silk_LSHIFT( state->width_prev_Q14, 10 );
202	13.0M	denom_Q16 = silk_DIV32_16( (opus_int32)1 << 16, STEREO_INTERP_LEN_MS * fs_kHz );
203	13.0M	delta0_Q13 = -silk_RSHIFT_ROUND( silk_SMULBB( pred_Q13[ 0 ] - state->pred_prev_Q13[ 0 ], denom_Q16 ), 16 );
204	13.0M	delta1_Q13 = -silk_RSHIFT_ROUND( silk_SMULBB( pred_Q13[ 1 ] - state->pred_prev_Q13[ 1 ], denom_Q16 ), 16 );
205	13.0M	deltaw_Q24 = silk_LSHIFT( silk_SMULWB( width_Q14 - state->width_prev_Q14, denom_Q16 ), 10 );
206	1.13G	for( n = 0; n < STEREO_INTERP_LEN_MS * fs_kHz; n++ ) {
207	1.12G	pred0_Q13 += delta0_Q13;
208	1.12G	pred1_Q13 += delta1_Q13;
209	1.12G	w_Q24 += deltaw_Q24;
210	1.12G	sum = silk_LSHIFT( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 9 ); /* Q11 */
211	1.12G	sum = silk_SMLAWB( silk_SMULWB( w_Q24, side[ n + 1 ] ), sum, pred0_Q13 ); /* Q8 */
212	1.12G	sum = silk_SMLAWB( sum, silk_LSHIFT( (opus_int32)mid[ n + 1 ], 11 ), pred1_Q13 ); /* Q8 */
213	1.12G	x2[ n - 1 ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( sum, 8 ) );
214	1.12G	}
215
216	13.0M	pred0_Q13 = -pred_Q13[ 0 ];
217	13.0M	pred1_Q13 = -pred_Q13[ 1 ];
218	13.0M	w_Q24 = silk_LSHIFT( width_Q14, 10 );
219	1.13G	for( n = STEREO_INTERP_LEN_MS * fs_kHz; n < frame_length; n++ ) {
220	1.12G	sum = silk_LSHIFT( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 9 ); /* Q11 */
221	1.12G	sum = silk_SMLAWB( silk_SMULWB( w_Q24, side[ n + 1 ] ), sum, pred0_Q13 ); /* Q8 */
222	1.12G	sum = silk_SMLAWB( sum, silk_LSHIFT( (opus_int32)mid[ n + 1 ], 11 ), pred1_Q13 ); /* Q8 */
223	1.12G	x2[ n - 1 ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( sum, 8 ) );
224	1.12G	}
225	13.0M	state->pred_prev_Q13[ 0 ] = (opus_int16)pred_Q13[ 0 ];
226	13.0M	state->pred_prev_Q13[ 1 ] = (opus_int16)pred_Q13[ 1 ];
227	13.0M	state->width_prev_Q14 = (opus_int16)width_Q14;
228	13.0M	RESTORE_STACK;
229	13.0M	}