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/* * | |
* SKP_Silk_LPC_synthesis_filter.c * | |
* Coefficients are in Q12 * | |
* * | |
* even order AR filter * | |
* */ | |
#include "SKP_Silk_SigProc_FIX.h" | |
/* even order AR filter */ | |
void SKP_Silk_LPC_synthesis_filter( | |
const SKP_int16 *in, /* I: excitation signal */ | |
const SKP_int16 *A_Q12, /* I: AR coefficients [Order], between -8_Q0 and 8_Q0 */ | |
const SKP_int32 Gain_Q26, /* I: gain */ | |
SKP_int32 *S, /* I/O: state vector [Order] */ | |
SKP_int16 *out, /* O: output signal */ | |
const SKP_int32 len, /* I: signal length */ | |
const SKP_int Order /* I: filter order, must be even */ | |
) | |
{ | |
SKP_int k, j, idx, Order_half = SKP_RSHIFT( Order, 1 ); | |
SKP_int32 SA, SB, out32_Q10, out32; | |
/* Order must be even */ | |
SKP_assert( 2 * Order_half == Order ); | |
/* S[] values are in Q14 */ | |
for( k = 0; k < len; k++ ) { | |
SA = S[ Order - 1 ]; | |
out32_Q10 = 0; | |
for( j = 0; j < ( Order_half - 1 ); j++ ) { | |
idx = SKP_SMULBB( 2, j ) + 1; | |
SB = S[ Order - 1 - idx ]; | |
S[ Order - 1 - idx ] = SA; | |
out32_Q10 = SKP_SMLAWB( out32_Q10, SA, A_Q12[ ( j << 1 ) ] ); | |
out32_Q10 = SKP_SMLAWB( out32_Q10, SB, A_Q12[ ( j << 1 ) + 1 ] ); | |
SA = S[ Order - 2 - idx ]; | |
S[ Order - 2 - idx ] = SB; | |
} | |
/* unrolled loop: epilog */ | |
SB = S[ 0 ]; | |
S[ 0 ] = SA; | |
out32_Q10 = SKP_SMLAWB( out32_Q10, SA, A_Q12[ Order - 2 ] ); | |
out32_Q10 = SKP_SMLAWB( out32_Q10, SB, A_Q12[ Order - 1 ] ); | |
/* apply gain to excitation signal and add to prediction */ | |
out32_Q10 = SKP_ADD_SAT32( out32_Q10, SKP_SMULWB( Gain_Q26, in[ k ] ) ); | |
/* scale to Q0 */ | |
out32 = SKP_RSHIFT_ROUND( out32_Q10, 10 ); | |
/* saturate output */ | |
out[ k ] = ( SKP_int16 )SKP_SAT16( out32 ); | |
/* move result into delay line */ | |
S[ Order - 1 ] = SKP_LSHIFT_SAT32( out32_Q10, 4 ); | |
} | |
} |