ref: 310af750eb5726b4143a43208f2bc03677c6f5db
dir: /silk/SKP_Silk_stereo_LR_to_MS.c/
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#include "SKP_Silk_main.h"
/* Convert Left/Right stereo signal to adaptive Mid/Side representation */
void SKP_Silk_stereo_LR_to_MS(
stereo_state *state, /* I/O State */
SKP_int16 x1[], /* I/O Left input signal, becomes mid signal */
SKP_int16 x2[], /* I/O Right input signal, becomes side signal */
SKP_int *predictorIx, /* O Index for predictor filter */
SKP_int fs_kHz, /* I Samples rate (kHz) */
SKP_int frame_length /* I Number of samples */
)
{
SKP_int n, scale, scale1, scale2;
SKP_int32 sum, diff, nrg1, nrg2, corr, predictor_Q16, pred_Q16, delta_Q16;
/* Convert to basic mid/side signals */
for( n = 0; n < frame_length; n++ ) {
sum = x1[ n ] + (SKP_int32)x2[ n ];
diff = x1[ n ] - (SKP_int32)x2[ n ];
x1[ n ] = (SKP_int16)SKP_RSHIFT32( sum + 1, 1 );
x2[ n ] = (SKP_int16)SKP_RSHIFT32( diff, 1 );
}
/* Find predictor */
SKP_Silk_sum_sqr_shift( &nrg1, &scale1, x1, frame_length );
SKP_Silk_sum_sqr_shift( &nrg2, &scale2, x2, frame_length );
if( scale1 > scale2 ) {
scale = scale1;
} else {
scale = scale2;
nrg1 = SKP_RSHIFT32( nrg1, scale2 - scale1 );
}
corr = SKP_Silk_inner_prod_aligned_scale( x1, x2, scale, frame_length );
predictor_Q16 = SKP_DIV32_varQ( corr, nrg1 + 1, 16 );
/* Hysteresis */
if( predictor_Q16 > state->predictor_prev_Q16 ) {
predictor_Q16 -= SKP_FIX_CONST( STEREO_QUANT_HYSTERESIS / STEREO_QUANT_STEPS, 16 );
} else {
predictor_Q16 += SKP_FIX_CONST( STEREO_QUANT_HYSTERESIS / STEREO_QUANT_STEPS, 16 );
}
/* Quantize */
*predictorIx = SKP_RSHIFT_ROUND( SKP_MUL( predictor_Q16 + 65536, STEREO_QUANT_STEPS - 1 ), 17 );
*predictorIx = SKP_LIMIT( *predictorIx, 0, STEREO_QUANT_STEPS - 1 );
predictor_Q16 = SKP_SMLABB( -65536, *predictorIx, ( 1 << 17 ) / ( STEREO_QUANT_STEPS - 1 ) );
/* Subtract prediction from side channel */
if( predictor_Q16 != state->predictor_prev_Q16 ) {
/* Interpolate predictor */
pred_Q16 = -state->predictor_prev_Q16;
delta_Q16 = -SKP_DIV32_16( predictor_Q16 - state->predictor_prev_Q16, STEREO_INTERPOL_LENGTH_MS * fs_kHz );
for( n = 0; n < STEREO_INTERPOL_LENGTH_MS * fs_kHz; n++ ) {
pred_Q16 += delta_Q16;
x2[ n ] = (SKP_int16)SKP_SAT16( SKP_SMLAWB( x2[ n ], pred_Q16, x1[ n ] ) );
}
} else {
n = 0;
}
pred_Q16 = -predictor_Q16;
for( ; n < frame_length; n++ ) {
x2[ n ] = (SKP_int16)SKP_SAT16( SKP_SMLAWB( x2[ n ], pred_Q16, x1[ n ] ) );
}
state->predictor_prev_Q16 = predictor_Q16;
}