ref: 38c6a150926d83af381025523219dc441ee6f4c8
dir: /silk/fixed/schur64_FIX.c/
/***********************************************************************
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "SigProc_FIX.h"
/* Slower than schur(), but more accurate. */
/* Uses SMULL(), available on armv4 */
opus_int32 silk_schur64( /* O returns residual energy */
opus_int32 rc_Q16[], /* O Reflection coefficients [order] Q16 */
const opus_int32 c[], /* I Correlations [order+1] */
opus_int32 order /* I Prediction order */
)
{
opus_int k, n;
opus_int32 C[ SILK_MAX_ORDER_LPC + 1 ][ 2 ];
opus_int32 Ctmp1_Q30, Ctmp2_Q30, rc_tmp_Q31;
silk_assert( order==6||order==8||order==10||order==12||order==14||order==16 );
/* Check for invalid input */
if( c[ 0 ] <= 0 ) {
silk_memset( rc_Q16, 0, order * sizeof( opus_int32 ) );
return 0;
}
for( k = 0; k < order + 1; k++ ) {
C[ k ][ 0 ] = C[ k ][ 1 ] = c[ k ];
}
for( k = 0; k < order; k++ ) {
/* Get reflection coefficient: divide two Q30 values and get result in Q31 */
rc_tmp_Q31 = silk_DIV32_varQ( -C[ k + 1 ][ 0 ], C[ 0 ][ 1 ], 31 );
/* Save the output */
rc_Q16[ k ] = silk_RSHIFT_ROUND( rc_tmp_Q31, 15 );
/* Update correlations */
for( n = 0; n < order - k; n++ ) {
Ctmp1_Q30 = C[ n + k + 1 ][ 0 ];
Ctmp2_Q30 = C[ n ][ 1 ];
/* Multiply and add the highest int32 */
C[ n + k + 1 ][ 0 ] = Ctmp1_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp2_Q30, 1 ), rc_tmp_Q31 );
C[ n ][ 1 ] = Ctmp2_Q30 + silk_SMMUL( silk_LSHIFT( Ctmp1_Q30, 1 ), rc_tmp_Q31 );
}
}
return( C[ 0 ][ 1 ] );
}