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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;
}
