ref: 0335534fe6a01ed747992c341118c998a4b10b9d
dir: /silk/stereo_find_predictor.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "main.h"
/* Find least-squares prediction gain for one signal based on another and quantize it */
opus_int32 silk_stereo_find_predictor( /* O Returns predictor in Q13 */
opus_int32 *ratio_Q14, /* O Ratio of residual and mid energies */
const opus_int16 x[], /* I Basis signal */
const opus_int16 y[], /* I Target signal */
opus_int32 mid_res_amp_Q0[], /* I/O Smoothed mid, residual norms */
opus_int length, /* I Number of samples */
opus_int smooth_coef_Q16 /* I Smoothing coefficient */
)
{
opus_int scale, scale1, scale2;
opus_int32 nrgx, nrgy, corr, pred_Q13, pred2_Q10;
/* Find predictor */
silk_sum_sqr_shift( &nrgx, &scale1, x, length );
silk_sum_sqr_shift( &nrgy, &scale2, y, length );
scale = silk_max_int( scale1, scale2 );
scale = scale + ( scale & 1 ); /* make even */
nrgy = silk_RSHIFT32( nrgy, scale - scale2 );
nrgx = silk_RSHIFT32( nrgx, scale - scale1 );
nrgx = silk_max_int( nrgx, 1 );
corr = silk_inner_prod_aligned_scale( x, y, scale, length );
pred_Q13 = silk_DIV32_varQ( corr, nrgx, 13 );
pred_Q13 = silk_LIMIT( pred_Q13, -(1 << 14), 1 << 14 );
pred2_Q10 = silk_SMULWB( pred_Q13, pred_Q13 );
/* Faster update for signals with large prediction parameters */
smooth_coef_Q16 = (opus_int)silk_max_int( smooth_coef_Q16, silk_abs( pred2_Q10 ) );
/* Smoothed mid and residual norms */
silk_assert( smooth_coef_Q16 < 32768 );
scale = silk_RSHIFT( scale, 1 );
mid_res_amp_Q0[ 0 ] = silk_SMLAWB( mid_res_amp_Q0[ 0 ], silk_LSHIFT( silk_SQRT_APPROX( nrgx ), scale ) - mid_res_amp_Q0[ 0 ],
smooth_coef_Q16 );
/* Residual energy = nrgy - 2 * pred * corr + pred^2 * nrgx */
nrgy = silk_SUB_LSHIFT32( nrgy, silk_SMULWB( corr, pred_Q13 ), 3 + 1 );
nrgy = silk_ADD_LSHIFT32( nrgy, silk_SMULWB( nrgx, pred2_Q10 ), 6 );
mid_res_amp_Q0[ 1 ] = silk_SMLAWB( mid_res_amp_Q0[ 1 ], silk_LSHIFT( silk_SQRT_APPROX( nrgy ), scale ) - mid_res_amp_Q0[ 1 ],
smooth_coef_Q16 );
/* Ratio of smoothed residual and mid norms */
*ratio_Q14 = silk_DIV32_varQ( mid_res_amp_Q0[ 1 ], silk_max( mid_res_amp_Q0[ 0 ], 1 ), 14 );
*ratio_Q14 = silk_LIMIT( *ratio_Q14, 0, 32767 );
return pred_Q13;
}