ref: c77b96333b471c7b8a89852ee941e6a8987751b4
dir: /silk/SKP_Silk_schur64.c/
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#include "SKP_Silk_SigProc_FIX.h"
/* Slower than schur(), but more accurate. */
/* Uses SMULL(), available on armv4 */
SKP_int32 SKP_Silk_schur64( /* O: Returns residual energy */
SKP_int32 rc_Q16[], /* O: Reflection coefficients [order] Q16 */
const SKP_int32 c[], /* I: Correlations [order+1] */
SKP_int32 order /* I: Prediction order */
)
{
SKP_int k, n;
SKP_int32 C[ SKP_Silk_MAX_ORDER_LPC + 1 ][ 2 ];
SKP_int32 Ctmp1_Q30, Ctmp2_Q30, rc_tmp_Q31;
/* Check for invalid input */
if( c[ 0 ] <= 0 ) {
SKP_memset( rc_Q16, 0, order * sizeof( SKP_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 = SKP_DIV32_varQ( -C[ k + 1 ][ 0 ], C[ 0 ][ 1 ], 31 );
/* Save the output */
rc_Q16[ k ] = SKP_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 + SKP_SMMUL( SKP_LSHIFT( Ctmp2_Q30, 1 ), rc_tmp_Q31 );
C[ n ][ 1 ] = Ctmp2_Q30 + SKP_SMMUL( SKP_LSHIFT( Ctmp1_Q30, 1 ), rc_tmp_Q31 );
}
}
return( C[ 0 ][ 1 ] );
}