michael@0: /***********************************************************************
michael@0: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
michael@0: Redistribution and use in source and binary forms, with or without
michael@0: modification, are permitted provided that the following conditions
michael@0: are met:
michael@0: - Redistributions of source code must retain the above copyright notice,
michael@0: this list of conditions and the following disclaimer.
michael@0: - Redistributions in binary form must reproduce the above copyright
michael@0: notice, this list of conditions and the following disclaimer in the
michael@0: documentation and/or other materials provided with the distribution.
michael@0: - Neither the name of Internet Society, IETF or IETF Trust, nor the
michael@0: names of specific contributors, may be used to endorse or promote
michael@0: products derived from this software without specific prior written
michael@0: permission.
michael@0: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
michael@0: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
michael@0: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
michael@0: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
michael@0: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
michael@0: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
michael@0: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
michael@0: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
michael@0: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
michael@0: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
michael@0: POSSIBILITY OF SUCH DAMAGE.
michael@0: ***********************************************************************/
michael@0: 
michael@0: #ifdef HAVE_CONFIG_H
michael@0: #include "config.h"
michael@0: #endif
michael@0: 
michael@0: #include "SigProc_FIX.h"
michael@0: 
michael@0: /* Slower than schur(), but more accurate.                              */
michael@0: /* Uses SMULL(), available on armv4                                     */
michael@0: opus_int32 silk_schur64(                            /* O    returns residual energy                                     */
michael@0:     opus_int32                  rc_Q16[],           /* O    Reflection coefficients [order] Q16                         */
michael@0:     const opus_int32            c[],                /* I    Correlations [order+1]                                      */
michael@0:     opus_int32                  order               /* I    Prediction order                                            */
michael@0: )
michael@0: {
michael@0:     opus_int   k, n;
michael@0:     opus_int32 C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
michael@0:     opus_int32 Ctmp1_Q30, Ctmp2_Q30, rc_tmp_Q31;
michael@0: 
michael@0:     silk_assert( order==6||order==8||order==10||order==12||order==14||order==16 );
michael@0: 
michael@0:     /* Check for invalid input */
michael@0:     if( c[ 0 ] <= 0 ) {
michael@0:         silk_memset( rc_Q16, 0, order * sizeof( opus_int32 ) );
michael@0:         return 0;
michael@0:     }
michael@0: 
michael@0:     for( k = 0; k < order + 1; k++ ) {
michael@0:         C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
michael@0:     }
michael@0: 
michael@0:     for( k = 0; k < order; k++ ) {
michael@0:         /* Check that we won't be getting an unstable rc, otherwise stop here. */
michael@0:         if (silk_abs_int32(C[ k + 1 ][ 0 ]) >= C[ 0 ][ 1 ]) {
michael@0:            if ( C[ k + 1 ][ 0 ] > 0 ) {
michael@0:               rc_Q16[ k ] = -SILK_FIX_CONST( .99f, 16 );
michael@0:            } else {
michael@0:               rc_Q16[ k ] = SILK_FIX_CONST( .99f, 16 );
michael@0:            }
michael@0:            k++;
michael@0:            break;
michael@0:         }
michael@0: 
michael@0:         /* Get reflection coefficient: divide two Q30 values and get result in Q31 */
michael@0:         rc_tmp_Q31 = silk_DIV32_varQ( -C[ k + 1 ][ 0 ], C[ 0 ][ 1 ], 31 );
michael@0: 
michael@0:         /* Save the output */
michael@0:         rc_Q16[ k ] = silk_RSHIFT_ROUND( rc_tmp_Q31, 15 );
michael@0: 
michael@0:         /* Update correlations */
michael@0:         for( n = 0; n < order - k; n++ ) {
michael@0:             Ctmp1_Q30 = C[ n + k + 1 ][ 0 ];
michael@0:             Ctmp2_Q30 = C[ n ][ 1 ];
michael@0: 
michael@0:             /* Multiply and add the highest int32 */
michael@0:             C[ n + k + 1 ][ 0 ] = Ctmp1_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp2_Q30, 1 ), rc_tmp_Q31 );
michael@0:             C[ n ][ 1 ]         = Ctmp2_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp1_Q30, 1 ), rc_tmp_Q31 );
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     for(; k < order; k++ ) {
michael@0:        rc_Q16[ k ] = 0;
michael@0:     }
michael@0: 
michael@0:     return silk_max_32( 1, C[ 0 ][ 1 ] );
michael@0: }