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: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
Chris@69: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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Chris@69: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
Chris@69: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
Chris@69: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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: /* Slower than schur(), but more accurate.                              */
Chris@69: /* Uses SMULL(), available on armv4                                     */
Chris@69: opus_int32 silk_schur64(                            /* O    returns residual energy                                     */
Chris@69:     opus_int32                  rc_Q16[],           /* O    Reflection coefficients [order] Q16                         */
Chris@69:     const opus_int32            c[],                /* I    Correlations [order+1]                                      */
Chris@69:     opus_int32                  order               /* I    Prediction order                                            */
Chris@69: )
Chris@69: {
Chris@69:     opus_int   k, n;
Chris@69:     opus_int32 C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
Chris@69:     opus_int32 Ctmp1_Q30, Ctmp2_Q30, rc_tmp_Q31;
Chris@69: 
Chris@69:     celt_assert( order >= 0 && order <= SILK_MAX_ORDER_LPC );
Chris@69: 
Chris@69:     /* Check for invalid input */
Chris@69:     if( c[ 0 ] <= 0 ) {
Chris@69:         silk_memset( rc_Q16, 0, order * sizeof( opus_int32 ) );
Chris@69:         return 0;
Chris@69:     }
Chris@69: 
Chris@69:     k = 0;
Chris@69:     do {
Chris@69:         C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
Chris@69:     } while( ++k <= order );
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_Q16[ k ] = -SILK_FIX_CONST( .99f, 16 );
Chris@69:            } else {
Chris@69:               rc_Q16[ k ] = SILK_FIX_CONST( .99f, 16 );
Chris@69:            }
Chris@69:            k++;
Chris@69:            break;
Chris@69:         }
Chris@69: 
Chris@69:         /* Get reflection coefficient: divide two Q30 values and get result in Q31 */
Chris@69:         rc_tmp_Q31 = silk_DIV32_varQ( -C[ k + 1 ][ 0 ], C[ 0 ][ 1 ], 31 );
Chris@69: 
Chris@69:         /* Save the output */
Chris@69:         rc_Q16[ k ] = silk_RSHIFT_ROUND( rc_tmp_Q31, 15 );
Chris@69: 
Chris@69:         /* Update correlations */
Chris@69:         for( n = 0; n < order - k; n++ ) {
Chris@69:             Ctmp1_Q30 = C[ n + k + 1 ][ 0 ];
Chris@69:             Ctmp2_Q30 = C[ n ][ 1 ];
Chris@69: 
Chris@69:             /* Multiply and add the highest int32 */
Chris@69:             C[ n + k + 1 ][ 0 ] = Ctmp1_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp2_Q30, 1 ), rc_tmp_Q31 );
Chris@69:             C[ n ][ 1 ]         = Ctmp2_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp1_Q30, 1 ), rc_tmp_Q31 );
Chris@69:         }
Chris@69:     }
Chris@69: 
Chris@69:     for(; k < order; k++ ) {
Chris@69:        rc_Q16[ k ] = 0;
Chris@69:     }
Chris@69: 
Chris@69:     return silk_max_32( 1, C[ 0 ][ 1 ] );
Chris@69: }