opus/silk/fixed/burg_modified_FIX.c

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

#include "SigProc_FIX.h"
#include "define.h"
#include "tuning_parameters.h"
#include "pitch.h"

/* This code implements the method from https://www.opus-codec.org/docs/vos_fastburg.pdf */

#define QA                          25
#define N_BITS_HEAD_ROOM            2
#define MIN_RSHIFTS                 -16
#define MAX_RSHIFTS                 (32 - QA)

/* Compute reflection coefficients from input signal */
void silk_burg_modified_c(
    opus_int32                  *res_nrg,           /* O    Residual energy                                             */
    opus_int                    *res_nrg_Q,         /* O    Residual energy Q value                                     */
    opus_int32                  A_Q16[],            /* O    Prediction coefficients (length order)                      */
    const opus_int16            x[],                /* I    Input signal, length: nb_subfr * ( D + subfr_length )       */
    const opus_int32            minInvGain_Q30,     /* I    Inverse of max prediction gain                              */
    const opus_int              subfr_length,       /* I    Input signal subframe length (incl. D preceding samples)    */
    const opus_int              nb_subfr,           /* I    Number of subframes stacked in x                            */
    const opus_int              D,                  /* I    Order                                                       */
    int                         arch                /* I    Run-time architecture                                       */
)
{
    opus_int         k, n, s, lz, rshifts, rshifts_extra, reached_max_gain;
    opus_int32       C0, num, nrg, rc_Q31, invGain_Q30, Atmp_QA, Atmp1, tmp1, tmp2, x1, x2;
    const opus_int16 *x_ptr;
    opus_int32       Af_QA[ SILK_MAX_ORDER_LPC ];
    opus_int32       g[ SILK_MAX_ORDER_LPC + 1 ];
    opus_int32       c[ SILK_MAX_ORDER_LPC + 1 ];

    /* Compute autocorrelations, added over subframes */
    silk_sum_sqr_shift( &C0, &rshifts, x, nb_subfr * subfr_length );
    if( rshifts > MAX_RSHIFTS ) {
        C0 = silk_LSHIFT32( C0, rshifts - MAX_RSHIFTS );
        silk_assert( C0 > 0 );
        rshifts = MAX_RSHIFTS;
    } else {
        lz = silk_CLZ32( C0 ) - 1;
        rshifts_extra = N_BITS_HEAD_ROOM - lz;
        if( rshifts_extra > 0 ) {
            rshifts_extra = silk_min( rshifts_extra, MAX_RSHIFTS - rshifts );
            C0 = silk_RSHIFT32( C0, rshifts_extra );
        } else {
            rshifts_extra = silk_max( rshifts_extra, MIN_RSHIFTS - rshifts );
            C0 = silk_LSHIFT32( C0, -rshifts_extra );
        }
        rshifts += rshifts_extra;
    }
    silk_memset( c, 0, (D+1) * sizeof( opus_int32 ) );
    if( rshifts > 0 ) {
        for( s = 0; s < nb_subfr; s++ ) {
            x_ptr = x + s * subfr_length;
            for( n = 1; n < D + 1; n++ ) {
                c[ n ] += (opus_int32)silk_RSHIFT64(
                    silk_inner_prod16_aligned_64( x_ptr, x_ptr + n, subfr_length - n, arch ), rshifts );
            }
        }
    } else {
        for( s = 0; s < nb_subfr; s++ ) {
            int i;
		    opus_int32 xcorr[ SILK_MAX_ORDER_LPC ];
            opus_int32 d;
            x_ptr = x + s * subfr_length;
            celt_pitch_xcorr(x_ptr, x_ptr + 1, xcorr, subfr_length - D, D, arch );
            for( n = 1; n < D + 1; n++ ) {
               for ( i = n + subfr_length - D, d = 0; i < subfr_length; i++ )
                  d = MAC16_16( d, x_ptr[ i ], x_ptr[ i - n ] );
               xcorr[ n - 1 ] += d;
            }
            for( n = 1; n < D + 1; n++ ) {
                c[ n ] += silk_LSHIFT32( xcorr[ n - 1 ], -rshifts );
            }
        }
    }

	/* Multiply all correlations by 2 */
	rshifts++;

    /* Initialize */
	c[ 0 ] = C0 + silk_SMMUL( SILK_FIX_CONST( FIND_LPC_COND_FAC, 32 ), C0 ) + 1;                        /* Q(-rshifts) */
	g[ 0 ] = c[ 0 ];																					/* Q(-rshifts) */
	tmp1 = 0;
    if( rshifts > -N_BITS_HEAD_ROOM ) {
		for( s = 0; s < nb_subfr; s++ ) {
			x_ptr = x + s * subfr_length;
			x1 = x_ptr[ 0 ];
			x2 = x_ptr[ subfr_length - 1 ];
			tmp1 = silk_SMLAWB( tmp1, silk_LSHIFT32( x1, 16 - rshifts ), x1 );							/* Q(-rshifts) */
			tmp1 = silk_SMLAWB( tmp1, silk_LSHIFT32( x2, 16 - rshifts ), x2 );							/* Q(-rshifts) */
		}
	} else {
		for( s = 0; s < nb_subfr; s++ ) {
			x_ptr = x + s * subfr_length;
			x1 = x_ptr[ 0 ];
			x2 = x_ptr[ subfr_length - 1 ];
			tmp1 = silk_MLA( tmp1, silk_LSHIFT32( x1, -rshifts ), x1 );									/* Q(-rshifts) */
			tmp1 = silk_MLA( tmp1, silk_LSHIFT32( x2, -rshifts ), x2 );									/* Q(-rshifts) */
		}
	}
	g[ 0 ] -= tmp1;
	g[ 1 ] = c[ 1 ];
	silk_assert( g[ 1 ] < g[ 0 ] && g[ 1 ] > -g[ 0 ] );
    rc_Q31 = -silk_DIV32_varQ( g[ 1 ], g[ 0 ], 31 );
	Af_QA[ 0 ] = silk_RSHIFT32( rc_Q31, 31 - QA );														/* QA */
    invGain_Q30 = SILK_FIX_CONST( 1, 30 ) - silk_SMMUL( rc_Q31, rc_Q31 );
    reached_max_gain = 0;
    for( n = 1; n < D; n++ ) {
        for( k = 0; k < (n >> 1) + 1; k++ ) {
            tmp1 = g[ k ];
            tmp2 = g[ n - k ];
            g[ k ]     = silk_ADD_LSHIFT32( tmp1, silk_SMMUL( tmp2, rc_Q31 ), 1 );						/* Q(-rshifts) */
            g[ n - k ] = silk_ADD_LSHIFT32( tmp2, silk_SMMUL( tmp1, rc_Q31 ), 1 );						/* Q(-rshifts) */
        }
        if( rshifts > -N_BITS_HEAD_ROOM ) {
            for( s = 0; s < nb_subfr; s++ ) {
                x_ptr = x + s * subfr_length;
                x1  = -silk_LSHIFT32( (opus_int32)x_ptr[ n ],                    16 - rshifts );        /* Q(16-rshifts) */
                x2  = -silk_LSHIFT32( (opus_int32)x_ptr[ subfr_length - n - 1 ], 16 - rshifts );        /* Q(16-rshifts) */
                tmp1 = silk_LSHIFT32( (opus_int32)x_ptr[ n ],                    QA - 16 );             /* Q(QA-16) */
                tmp2 = silk_LSHIFT32( (opus_int32)x_ptr[ subfr_length - n - 1 ], QA - 16 );             /* Q(QA-16) */
                for( k = 0; k < n; k++ ) {
                    c[ k + 1 ] = silk_SMLAWB( silk_SMLAWB( c[ k + 1 ], x1, x_ptr[ n - k - 1 ] ),		/* Q( -rshifts ) */
														               x2, x_ptr[ subfr_length - n + k ] );
                    Atmp_QA = Af_QA[ k ];
                    tmp1 = silk_SMLAWB( tmp1, Atmp_QA, x_ptr[ n - k - 1 ]            );                 /* Q(QA-16) */
                    tmp2 = silk_SMLAWB( tmp2, Atmp_QA, x_ptr[ subfr_length - n + k ] );                 /* Q(QA-16) */
                }
				tmp1 = silk_LSHIFT32( -tmp1, 32 - QA - rshifts );                                       /* Q(16-rshifts) */
                tmp2 = silk_LSHIFT32( -tmp2, 32 - QA - rshifts );                                       /* Q(16-rshifts) */
                for( k = 0; k <= n; k++ ) {
                    g[ k ] = silk_SMLAWB( silk_SMLAWB( g[ k ], tmp1, x_ptr[ n - k ] ),					/* Q( -rshift ) */
                                                               tmp2, x_ptr[ subfr_length - n + k - 1 ] );
                }
            }
        } else {
            for( s = 0; s < nb_subfr; s++ ) {
                x_ptr = x + s * subfr_length;
				x1  = -silk_LSHIFT32( (opus_int32)x_ptr[ n ],                    -rshifts );            /* Q( -rshifts ) */
                x2  = -silk_LSHIFT32( (opus_int32)x_ptr[ subfr_length - n - 1 ], -rshifts );            /* Q( -rshifts ) */
                tmp1 = silk_LSHIFT32( (opus_int32)x_ptr[ n ],                    17 );                  /* Q17 */
                tmp2 = silk_LSHIFT32( (opus_int32)x_ptr[ subfr_length - n - 1 ], 17 );                  /* Q17 */
                for( k = 0; k < n; k++ ) {
                    c[ k + 1 ] = silk_MLA( silk_MLA( c[ k + 1 ], x1, x_ptr[ n - k - 1 ] ),				/* Q( -rshifts ) */
																 x2, x_ptr[ subfr_length - n + k ] );
                    Atmp1 = silk_RSHIFT_ROUND( Af_QA[ k ], QA - 17 );                                   /* Q17 */
                    tmp1 = silk_MLA( tmp1, x_ptr[ n - k - 1 ],            Atmp1 );                      /* Q17 */
                    tmp2 = silk_MLA( tmp2, x_ptr[ subfr_length - n + k ], Atmp1 );                      /* Q17 */
                }
                tmp1 = -tmp1;                                                                           /* Q17 */
                tmp2 = -tmp2;                                                                           /* Q17 */
                for( k = 0; k <= n; k++ ) {
                    g[ k ] = silk_SMLAWW( silk_SMLAWW( g[ k ],											/* Q( -rshift ) */
								tmp1, silk_LSHIFT32( (opus_int32)x_ptr[ n - k ], -rshifts - 1 ) ),
								tmp2, silk_LSHIFT32( (opus_int32)x_ptr[ subfr_length - n + k - 1 ], -rshifts - 1 ) );
                }
            }
        }

        /* Calculate nominator and denominator for the next order reflection (parcor) coefficient */
        tmp1 = c[ n + 1 ];																				/* Q( -rshifts ) */
        num  = 0;                                                                                       /* Q( -rshifts ) */
        nrg  = g[ 0 ];																					/* Q( -rshifts ) */
        for( k = 0; k < n; k++ ) {
            Atmp_QA = Af_QA[ k ];
            lz = silk_CLZ32( silk_abs( Atmp_QA ) ) - 1;
            lz = silk_min( 32 - QA, lz );
            Atmp1 = silk_LSHIFT32( Atmp_QA, lz );                                                       /* Q( QA + lz ) */
            tmp1 = silk_ADD_LSHIFT32( tmp1, silk_SMMUL( c[ n - k ], Atmp1 ), 32 - QA - lz );			/* Q( -rshifts ) */
            num  = silk_ADD_LSHIFT32( num,  silk_SMMUL( g[ n - k ], Atmp1 ), 32 - QA - lz );			/* Q( -rshifts ) */
            nrg  = silk_ADD_LSHIFT32( nrg,  silk_SMMUL( g[ k + 1 ], Atmp1 ), 32 - QA - lz );			/* Q( -rshifts ) */
        }
        g[ n + 1 ] = tmp1;																				/* Q( -rshifts ) */
        num = silk_ADD32( num, tmp1 );                                                                  /* Q( -rshifts ) */
        silk_assert( nrg > 0 );

        /* Calculate the next order reflection (parcor) coefficient */
        if( silk_abs( num ) < nrg ) {
            rc_Q31 = -silk_DIV32_varQ( num, nrg, 31 );
        } else {
            rc_Q31 = ( num > 0 ) ? silk_int32_MIN : silk_int32_MAX;
        }

        /* Update inverse prediction gain */
		tmp1 = SILK_FIX_CONST( 1, 30 ) - silk_SMMUL( rc_Q31, rc_Q31 );
        tmp1 = silk_LSHIFT( silk_SMMUL( invGain_Q30, tmp1 ), 2 );
        if( tmp1 <= minInvGain_Q30 ) {
            /* Max prediction gain exceeded; set reflection coefficient such that max prediction gain is exactly hit */
            tmp2 = SILK_FIX_CONST( 1, 30 ) - silk_DIV32_varQ( minInvGain_Q30, invGain_Q30, 30 );        /* Q30 */
            rc_Q31 = silk_SQRT_APPROX( tmp2 );															/* Q15 */
            if( rc_Q31 > 0 ) {
                /* Newton-Raphson iteration */
                rc_Q31 = silk_RSHIFT32( rc_Q31 + silk_DIV32( tmp2, rc_Q31 ), 1 );                       /* Q15 */
                rc_Q31 = silk_LSHIFT32( rc_Q31, 16 );                                                   /* Q31 */
                if( num < 0 ) {
                    /* Ensure adjusted reflection coefficients has the original sign */
                    rc_Q31 = -rc_Q31;
                }
            }
            invGain_Q30 = minInvGain_Q30;
            reached_max_gain = 1;
        } else {
            invGain_Q30 = tmp1;
        }

        /* Update the AR coefficients */
        for( k = 0; k < (n + 1) >> 1; k++ ) {
            tmp1 = Af_QA[ k ];																			/* QA */
            tmp2 = Af_QA[ n - k - 1 ];																	/* QA */
            Af_QA[ k ]         = silk_ADD_LSHIFT32( tmp1, silk_SMMUL( tmp2, rc_Q31 ), 1 );				/* QA */
            Af_QA[ n - k - 1 ] = silk_ADD_LSHIFT32( tmp2, silk_SMMUL( tmp1, rc_Q31 ), 1 );				/* QA */
        }
        Af_QA[ n ] = silk_RSHIFT32( rc_Q31, 31 - QA );													/* QA */

        if( reached_max_gain ) {
            /* Reached max prediction gain; set remaining coefficients to zero and exit loop */
            for( k = n + 1; k < D; k++ ) {
                Af_QA[ k ] = 0;
            }
            break;
        }
    }

	for( k = 0; k < D; k++ ) {
		/* Scale coefficients */
		A_Q16[ k ] = -silk_RSHIFT_ROUND( Af_QA[ k ], QA - 16 );
	}

    /* Subtract energy of preceding samples from C0 */
    rshifts--;  /* divide c0 by two */
    if( rshifts > 0 ) {
        for( s = 0; s < nb_subfr; s++ ) {
            x_ptr = x + s * subfr_length;
            C0 -= (opus_int32)silk_RSHIFT64( silk_inner_prod16_aligned_64( x_ptr, x_ptr, D, arch ), rshifts );
        }
    } else {
        for( s = 0; s < nb_subfr; s++ ) {
            x_ptr = x + s * subfr_length;
            C0 -= silk_LSHIFT32( silk_inner_prod_aligned( x_ptr, x_ptr, D, arch), -rshifts);
        }
    }
    /* Approximate residual energy */
    *res_nrg = silk_LSHIFT( silk_SMMUL( invGain_Q30, C0 ), 2 );
    *res_nrg_Q = -rshifts;
}