/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: 2025-10-10 07:38

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	133k	{
50	133k	opus_int n, is10msFrame, denom_Q16, delta0_Q13, delta1_Q13;
51	133k	opus_int32 sum, diff, smooth_coef_Q16, pred_Q13[ 2 ], pred0_Q13, pred1_Q13;
52	133k	opus_int32 LP_ratio_Q14, HP_ratio_Q14, frac_Q16, frac_3_Q16, min_mid_rate_bps, width_Q14, w_Q24, deltaw_Q24;
53	133k	VARDECL( opus_int16, side );
54	133k	VARDECL( opus_int16, LP_mid );
55	133k	VARDECL( opus_int16, HP_mid );
56	133k	VARDECL( opus_int16, LP_side );
57	133k	VARDECL( opus_int16, HP_side );
58	133k	opus_int16 *mid = &x1[ -2 ];
59	133k	SAVE_STACK;
60
61	133k	ALLOC( side, frame_length + 2, opus_int16 );
62		/* Convert to basic mid/side signals */
63	24.3M	for( n = 0; n < frame_length + 2; n++ ) {
64	24.1M	sum = x1[ n - 2 ] + (opus_int32)x2[ n - 2 ];
65	24.1M	diff = x1[ n - 2 ] - (opus_int32)x2[ n - 2 ];
66	24.1M	mid[ n ] = (opus_int16)silk_RSHIFT_ROUND( sum, 1 );
67	24.1M	side[ n ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( diff, 1 ) );
68	24.1M	}
69
70		/* Buffering */
71	133k	silk_memcpy( mid, state->sMid, 2 * sizeof( opus_int16 ) );
72	133k	silk_memcpy( side, state->sSide, 2 * sizeof( opus_int16 ) );
73	133k	silk_memcpy( state->sMid, &mid[ frame_length ], 2 * sizeof( opus_int16 ) );
74	133k	silk_memcpy( state->sSide, &side[ frame_length ], 2 * sizeof( opus_int16 ) );
75
76		/* LP and HP filter mid signal */
77	133k	ALLOC( LP_mid, frame_length, opus_int16 );
78	133k	ALLOC( HP_mid, frame_length, opus_int16 );
79	24.0M	for( n = 0; n < frame_length; n++ ) {
80	23.9M	sum = silk_RSHIFT_ROUND( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 2 );
81	23.9M	LP_mid[ n ] = sum;
82	23.9M	HP_mid[ n ] = mid[ n + 1 ] - sum;
83	23.9M	}
84
85		/* LP and HP filter side signal */
86	133k	ALLOC( LP_side, frame_length, opus_int16 );
87	133k	ALLOC( HP_side, frame_length, opus_int16 );
88	24.0M	for( n = 0; n < frame_length; n++ ) {
89	23.9M	sum = silk_RSHIFT_ROUND( silk_ADD_LSHIFT32( side[ n ] + (opus_int32)side[ n + 2 ], side[ n + 1 ], 1 ), 2 );
90	23.9M	LP_side[ n ] = sum;
91	23.9M	HP_side[ n ] = side[ n + 1 ] - sum;
92	23.9M	}
93
94		/* Find energies and predictors */
95	133k	is10msFrame = frame_length == 10 * fs_kHz;
96	133k	smooth_coef_Q16 = is10msFrame ?
97	22.5k	SILK_FIX_CONST( STEREO_RATIO_SMOOTH_COEF / 2, 16 ) :
98	133k	SILK_FIX_CONST( STEREO_RATIO_SMOOTH_COEF, 16 );
99	133k	smooth_coef_Q16 = silk_SMULWB( silk_SMULBB( prev_speech_act_Q8, prev_speech_act_Q8 ), smooth_coef_Q16 );
100
101	133k	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	133k	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	133k	frac_Q16 = silk_SMLABB( HP_ratio_Q14, LP_ratio_Q14, 3 );
105	133k	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	133k	total_rate_bps -= is10msFrame ? 1200 : 600; /* Subtract approximate bitrate for coding stereo parameters */
109	133k	if( total_rate_bps < 1 ) {
110	0	total_rate_bps = 1;
111	0	}
112	133k	min_mid_rate_bps = silk_SMLABB( 2000, fs_kHz, 600 );
113	133k	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	133k	frac_3_Q16 = silk_MUL( 3, frac_Q16 );
116	133k	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	133k	if( mid_side_rates_bps[ 0 ] < min_mid_rate_bps ) {
119	10.1k	mid_side_rates_bps[ 0 ] = min_mid_rate_bps;
120	10.1k	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	10.1k	width_Q14 = silk_DIV32_varQ( silk_LSHIFT( mid_side_rates_bps[ 1 ], 1 ) - min_mid_rate_bps,
123	10.1k	silk_SMULWB( SILK_FIX_CONST( 1, 16 ) + frac_3_Q16, min_mid_rate_bps ), 14+2 );
124	10.1k	width_Q14 = silk_LIMIT( width_Q14, 0, SILK_FIX_CONST( 1, 14 ) );
125	123k	} else {
126	123k	mid_side_rates_bps[ 1 ] = total_rate_bps - mid_side_rates_bps[ 0 ];
127	123k	width_Q14 = SILK_FIX_CONST( 1, 14 );
128	123k	}
129
130		/* Smoother */
131	133k	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	133k	*mid_only_flag = 0;
135	133k	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	133k	} else if( state->width_prev_Q14 == 0 &&
142	68.6k	( 8 * total_rate_bps < 13 * min_mid_rate_bps \|\| silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.05, 14 ) ) )
143	14.6k	{
144		/* Code as panned-mono; previous frame already had zero width */
145		/* Scale down and quantize predictors */
146	14.6k	pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
147	14.6k	pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
148	14.6k	silk_stereo_quant_pred( pred_Q13, ix );
149		/* Collapse stereo width */
150	14.6k	width_Q14 = 0;
151	14.6k	pred_Q13[ 0 ] = 0;
152	14.6k	pred_Q13[ 1 ] = 0;
153	14.6k	mid_side_rates_bps[ 0 ] = total_rate_bps;
154	14.6k	mid_side_rates_bps[ 1 ] = 0;
155	14.6k	*mid_only_flag = 1;
156	119k	} else if( state->width_prev_Q14 != 0 &&
157	65.0k	( 8 * total_rate_bps < 11 * min_mid_rate_bps \|\| silk_SMULWB( frac_Q16, state->smth_width_Q14 ) < SILK_FIX_CONST( 0.02, 14 ) ) )
158	3.05k	{
159		/* Transition to zero-width stereo */
160		/* Scale down and quantize predictors */
161	3.05k	pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
162	3.05k	pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
163	3.05k	silk_stereo_quant_pred( pred_Q13, ix );
164		/* Collapse stereo width */
165	3.05k	width_Q14 = 0;
166	3.05k	pred_Q13[ 0 ] = 0;
167	3.05k	pred_Q13[ 1 ] = 0;
168	116k	} else if( state->smth_width_Q14 > SILK_FIX_CONST( 0.95, 14 ) ) {
169		/* Full-width stereo coding */
170	116k	silk_stereo_quant_pred( pred_Q13, ix );
171	116k	width_Q14 = SILK_FIX_CONST( 1, 14 );
172	116k	} else {
173		/* Reduced-width stereo coding; scale down and quantize predictors */
174	0	pred_Q13[ 0 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 0 ] ), 14 );
175	0	pred_Q13[ 1 ] = silk_RSHIFT( silk_SMULBB( state->smth_width_Q14, pred_Q13[ 1 ] ), 14 );
176	0	silk_stereo_quant_pred( pred_Q13, ix );
177	0	width_Q14 = state->smth_width_Q14;
178	0	}
179
180		/* Make sure to keep on encoding until the tapered output has been transmitted */
181	133k	if( *mid_only_flag == 1 ) {
182	14.6k	state->silent_side_len += frame_length - STEREO_INTERP_LEN_MS * fs_kHz;
183	14.6k	if( state->silent_side_len < LA_SHAPE_MS * fs_kHz ) {
184	1.30k	*mid_only_flag = 0;
185	13.2k	} else {
186		/* Limit to avoid wrapping around */
187	13.2k	state->silent_side_len = 10000;
188	13.2k	}
189	119k	} else {
190	119k	state->silent_side_len = 0;
191	119k	}
192
193	133k	if( *mid_only_flag == 0 && mid_side_rates_bps[ 1 ] < 1 ) {
194	2.28k	mid_side_rates_bps[ 1 ] = 1;
195	2.28k	mid_side_rates_bps[ 0 ] = silk_max_int( 1, total_rate_bps - mid_side_rates_bps[ 1 ]);
196	2.28k	}
197
198		/* Interpolate predictors and subtract prediction from side channel */
199	133k	pred0_Q13 = -state->pred_prev_Q13[ 0 ];
200	133k	pred1_Q13 = -state->pred_prev_Q13[ 1 ];
201	133k	w_Q24 = silk_LSHIFT( state->width_prev_Q14, 10 );
202	133k	denom_Q16 = silk_DIV32_16( (opus_int32)1 << 16, STEREO_INTERP_LEN_MS * fs_kHz );
203	133k	delta0_Q13 = -silk_RSHIFT_ROUND( silk_SMULBB( pred_Q13[ 0 ] - state->pred_prev_Q13[ 0 ], denom_Q16 ), 16 );
204	133k	delta1_Q13 = -silk_RSHIFT_ROUND( silk_SMULBB( pred_Q13[ 1 ] - state->pred_prev_Q13[ 1 ], denom_Q16 ), 16 );
205	133k	deltaw_Q24 = silk_LSHIFT( silk_SMULWB( width_Q14 - state->width_prev_Q14, denom_Q16 ), 10 );
206	10.5M	for( n = 0; n < STEREO_INTERP_LEN_MS * fs_kHz; n++ ) {
207	10.4M	pred0_Q13 += delta0_Q13;
208	10.4M	pred1_Q13 += delta1_Q13;
209	10.4M	w_Q24 += deltaw_Q24;
210	10.4M	sum = silk_LSHIFT( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 9 ); /* Q11 */
211	10.4M	sum = silk_SMLAWB( silk_SMULWB( w_Q24, side[ n + 1 ] ), sum, pred0_Q13 ); /* Q8 */
212	10.4M	sum = silk_SMLAWB( sum, silk_LSHIFT( (opus_int32)mid[ n + 1 ], 11 ), pred1_Q13 ); /* Q8 */
213	10.4M	x2[ n - 1 ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( sum, 8 ) );
214	10.4M	}
215
216	133k	pred0_Q13 = -pred_Q13[ 0 ];
217	133k	pred1_Q13 = -pred_Q13[ 1 ];
218	133k	w_Q24 = silk_LSHIFT( width_Q14, 10 );
219	13.6M	for( n = STEREO_INTERP_LEN_MS * fs_kHz; n < frame_length; n++ ) {
220	13.4M	sum = silk_LSHIFT( silk_ADD_LSHIFT32( mid[ n ] + (opus_int32)mid[ n + 2 ], mid[ n + 1 ], 1 ), 9 ); /* Q11 */
221	13.4M	sum = silk_SMLAWB( silk_SMULWB( w_Q24, side[ n + 1 ] ), sum, pred0_Q13 ); /* Q8 */
222	13.4M	sum = silk_SMLAWB( sum, silk_LSHIFT( (opus_int32)mid[ n + 1 ], 11 ), pred1_Q13 ); /* Q8 */
223	13.4M	x2[ n - 1 ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( sum, 8 ) );
224	13.4M	}
225	133k	state->pred_prev_Q13[ 0 ] = (opus_int16)pred_Q13[ 0 ];
226	133k	state->pred_prev_Q13[ 1 ] = (opus_int16)pred_Q13[ 1 ];
227	133k	state->width_prev_Q14 = (opus_int16)width_Q14;
228	133k	RESTORE_STACK;
229	133k	}