Chris@69: /***********************************************************************
Chris@69: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
Chris@69: Redistribution and use in source and binary forms, with or without
Chris@69: modification, are permitted provided that the following conditions
Chris@69: are met:
Chris@69: - Redistributions of source code must retain the above copyright notice,
Chris@69: this list of conditions and the following disclaimer.
Chris@69: - Redistributions in binary form must reproduce the above copyright
Chris@69: notice, this list of conditions and the following disclaimer in the
Chris@69: documentation and/or other materials provided with the distribution.
Chris@69: - Neither the name of Internet Society, IETF or IETF Trust, nor the
Chris@69: names of specific contributors, may be used to endorse or promote
Chris@69: products derived from this software without specific prior written
Chris@69: permission.
Chris@69: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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Chris@69: POSSIBILITY OF SUCH DAMAGE.
Chris@69: ***********************************************************************/
Chris@69: 
Chris@69: #ifdef HAVE_CONFIG_H
Chris@69: #include "config.h"
Chris@69: #endif
Chris@69: 
Chris@69: #include "SigProc_FIX.h"
Chris@69: 
Chris@69: /* Faster than schur64(), but much less accurate.                       */
Chris@69: /* uses SMLAWB(), requiring armv5E and higher.                          */
Chris@69: opus_int32 silk_schur(                              /* O    Returns residual energy                                     */
Chris@69:     opus_int16                  *rc_Q15,            /* O    reflection coefficients [order] Q15                         */
Chris@69:     const opus_int32            *c,                 /* I    correlations [order+1]                                      */
Chris@69:     const opus_int32            order               /* I    prediction order                                            */
Chris@69: )
Chris@69: {
Chris@69:     opus_int        k, n, lz;
Chris@69:     opus_int32    C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
Chris@69:     opus_int32    Ctmp1, Ctmp2, rc_tmp_Q15;
Chris@69: 
Chris@69:     celt_assert( order >= 0 && order <= SILK_MAX_ORDER_LPC );
Chris@69: 
Chris@69:     /* Get number of leading zeros */
Chris@69:     lz = silk_CLZ32( c[ 0 ] );
Chris@69: 
Chris@69:     /* Copy correlations and adjust level to Q30 */
Chris@69:     k = 0;
Chris@69:     if( lz < 2 ) {
Chris@69:         /* lz must be 1, so shift one to the right */
Chris@69:         do {
Chris@69:             C[ k ][ 0 ] = C[ k ][ 1 ] = silk_RSHIFT( c[ k ], 1 );
Chris@69:         } while( ++k <= order );
Chris@69:     } else if( lz > 2 ) {
Chris@69:         /* Shift to the left */
Chris@69:         lz -= 2;
Chris@69:         do {
Chris@69:             C[ k ][ 0 ] = C[ k ][ 1 ] = silk_LSHIFT( c[ k ], lz );
Chris@69:         } while( ++k <= order );
Chris@69:     } else {
Chris@69:         /* No need to shift */
Chris@69:         do {
Chris@69:             C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
Chris@69:         } while( ++k <= order );
Chris@69:     }
Chris@69: 
Chris@69:     for( k = 0; k < order; k++ ) {
Chris@69:         /* Check that we won't be getting an unstable rc, otherwise stop here. */
Chris@69:         if (silk_abs_int32(C[ k + 1 ][ 0 ]) >= C[ 0 ][ 1 ]) {
Chris@69:            if ( C[ k + 1 ][ 0 ] > 0 ) {
Chris@69:               rc_Q15[ k ] = -SILK_FIX_CONST( .99f, 15 );
Chris@69:            } else {
Chris@69:               rc_Q15[ k ] = SILK_FIX_CONST( .99f, 15 );
Chris@69:            }
Chris@69:            k++;
Chris@69:            break;
Chris@69:         }
Chris@69: 
Chris@69:         /* Get reflection coefficient */
Chris@69:         rc_tmp_Q15 = -silk_DIV32_16( C[ k + 1 ][ 0 ], silk_max_32( silk_RSHIFT( C[ 0 ][ 1 ], 15 ), 1 ) );
Chris@69: 
Chris@69:         /* Clip (shouldn't happen for properly conditioned inputs) */
Chris@69:         rc_tmp_Q15 = silk_SAT16( rc_tmp_Q15 );
Chris@69: 
Chris@69:         /* Store */
Chris@69:         rc_Q15[ k ] = (opus_int16)rc_tmp_Q15;
Chris@69: 
Chris@69:         /* Update correlations */
Chris@69:         for( n = 0; n < order - k; n++ ) {
Chris@69:             Ctmp1 = C[ n + k + 1 ][ 0 ];
Chris@69:             Ctmp2 = C[ n ][ 1 ];
Chris@69:             C[ n + k + 1 ][ 0 ] = silk_SMLAWB( Ctmp1, silk_LSHIFT( Ctmp2, 1 ), rc_tmp_Q15 );
Chris@69:             C[ n ][ 1 ]         = silk_SMLAWB( Ctmp2, silk_LSHIFT( Ctmp1, 1 ), rc_tmp_Q15 );
Chris@69:         }
Chris@69:     }
Chris@69: 
Chris@69:     for(; k < order; k++ ) {
Chris@69:        rc_Q15[ k ] = 0;
Chris@69:     }
Chris@69: 
Chris@69:     /* return residual energy */
Chris@69:     return silk_max_32( 1, C[ 0 ][ 1 ] );
Chris@69: }