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-rw-r--r--silk/float/burg_modified_FLP.c162
1 files changed, 75 insertions, 87 deletions
diff --git a/silk/float/burg_modified_FLP.c b/silk/float/burg_modified_FLP.c
index ea5dc25a..7ef4cac2 100644
--- a/silk/float/burg_modified_FLP.c
+++ b/silk/float/burg_modified_FLP.c
@@ -33,11 +33,11 @@ POSSIBILITY OF SUCH DAMAGE.
#include "tuning_parameters.h"
#include "define.h"
-#define MAX_FRAME_SIZE 384 /* subfr_length * nb_subfr = ( 0.005 * 16000 + 16 ) * 4 = 384*/
+/* This code implements the method from https://www.opus-codec.org/docs/vos_fastburg.pdf */
/* Compute reflection coefficients from input signal */
-silk_float silk_burg_modified_FLP( /* O returns residual energy */
- silk_float A[], /* O prediction coefficients (length order) */
+silk_float silk_burg_modified_FLP(
+ silk_float af[], /* O prediction coefficients (length order) */
const silk_float x[], /* I input signal, length: nb_subfr*(D+L_sub) */
const silk_float minInvGain, /* I minimum inverse prediction gain */
const opus_int subfr_length, /* I input signal subframe length (incl. D preceding samples) */
@@ -46,75 +46,81 @@ silk_float silk_burg_modified_FLP( /* O returns residual energy
)
{
opus_int k, n, s, reached_max_gain;
- double C0, invGain, num, nrg_f, nrg_b, rc, Atmp, tmp1, tmp2;
+ double invGain, num, nrg, rc, tmp1, tmp2, x1, x2, atmp;
const silk_float *x_ptr;
- double C_first_row[ SILK_MAX_ORDER_LPC ], C_last_row[ SILK_MAX_ORDER_LPC ];
- double CAf[ SILK_MAX_ORDER_LPC + 1 ], CAb[ SILK_MAX_ORDER_LPC + 1 ];
- double Af[ SILK_MAX_ORDER_LPC ];
-
- silk_assert( subfr_length * nb_subfr <= MAX_FRAME_SIZE );
+ double c[ SILK_MAX_ORDER_LPC + 1 ];
+ double g[ SILK_MAX_ORDER_LPC + 1 ];
+ double a[ SILK_MAX_ORDER_LPC ];
/* Compute autocorrelations, added over subframes */
- C0 = silk_energy_FLP( x, nb_subfr * subfr_length );
- silk_memset( C_first_row, 0, SILK_MAX_ORDER_LPC * sizeof( double ) );
+ silk_memset( c, 0, (D + 1) * sizeof( double ) );
for( s = 0; s < nb_subfr; s++ ) {
x_ptr = x + s * subfr_length;
- for( n = 1; n < D + 1; n++ ) {
- C_first_row[ n - 1 ] += silk_inner_product_FLP( x_ptr, x_ptr + n, subfr_length - n );
+ for( n = 0; n < D + 1; n++ ) {
+ c[ n ] += silk_inner_product_FLP( x_ptr, x_ptr + n, subfr_length - n );
}
}
- silk_memcpy( C_last_row, C_first_row, SILK_MAX_ORDER_LPC * sizeof( double ) );
+ for( n = 0; n < D + 1; n++ ) {
+ c[ n ] *= 2.0;
+ }
/* Initialize */
- CAb[ 0 ] = CAf[ 0 ] = C0 + FIND_LPC_COND_FAC * C0 + 1e-9f;
- invGain = 1.0f;
+ c[ 0 ] += FIND_LPC_COND_FAC * c[ 0 ] + 1e-9f ;
+ g[ 0 ] = c[ 0 ];
+ tmp1 = 0.0f;
+ for( s = 0; s < nb_subfr; s++ ) {
+ x_ptr = x + s * subfr_length;
+ x1 = x_ptr[ 0 ];
+ x2 = x_ptr[ subfr_length - 1 ];
+ tmp1 += x1 * x1 + x2 * x2;
+ }
+ g[ 0 ] -= tmp1;
+ g[ 1 ] = c[ 1 ];
+ rc = - g[ 1 ] / g[ 0 ];
+ silk_assert( rc > -1.0 && rc < 1.0 );
+ a[ 0 ] = rc;
+ invGain = ( 1.0 - rc * rc );
reached_max_gain = 0;
- for( n = 0; n < D; n++ ) {
- /* Update first row of correlation matrix (without first element) */
- /* Update last row of correlation matrix (without last element, stored in reversed order) */
- /* Update C * Af */
- /* Update C * flipud(Af) (stored in reversed order) */
+ for( n = 1; n < D; n++ ) {
+ for( k = 0; k < (n >> 1) + 1; k++ ) {
+ tmp1 = g[ k ];
+ tmp2 = g[ n - k ];
+ g[ k ] = tmp1 + rc * tmp2;
+ g[ n - k ] = tmp2 + rc * tmp1;
+ }
for( s = 0; s < nb_subfr; s++ ) {
x_ptr = x + s * subfr_length;
- tmp1 = x_ptr[ n ];
- tmp2 = x_ptr[ subfr_length - n - 1 ];
+ x1 = x_ptr[ n ];
+ x2 = x_ptr[ subfr_length - n - 1 ];
+ tmp1 = x1;
+ tmp2 = x2;
for( k = 0; k < n; k++ ) {
- C_first_row[ k ] -= x_ptr[ n ] * x_ptr[ n - k - 1 ];
- C_last_row[ k ] -= x_ptr[ subfr_length - n - 1 ] * x_ptr[ subfr_length - n + k ];
- Atmp = Af[ k ];
- tmp1 += x_ptr[ n - k - 1 ] * Atmp;
- tmp2 += x_ptr[ subfr_length - n + k ] * Atmp;
+ atmp = a[ k ];
+ c[ k + 1 ] -= x1 * x_ptr[ n - k - 1 ] + x2 * x_ptr[ subfr_length - n + k ];
+ tmp1 += x_ptr[ n - k - 1 ] * atmp;
+ tmp2 += x_ptr[ subfr_length - n + k ] * atmp;
}
for( k = 0; k <= n; k++ ) {
- CAf[ k ] -= tmp1 * x_ptr[ n - k ];
- CAb[ k ] -= tmp2 * x_ptr[ subfr_length - n + k - 1 ];
+ g[ k ] -= tmp1 * x_ptr[ n - k ] + tmp2 * x_ptr[ subfr_length - n + k - 1 ];
}
}
- tmp1 = C_first_row[ n ];
- tmp2 = C_last_row[ n ];
- for( k = 0; k < n; k++ ) {
- Atmp = Af[ k ];
- tmp1 += C_last_row[ n - k - 1 ] * Atmp;
- tmp2 += C_first_row[ n - k - 1 ] * Atmp;
- }
- CAf[ n + 1 ] = tmp1;
- CAb[ n + 1 ] = tmp2;
/* Calculate nominator and denominator for the next order reflection (parcor) coefficient */
- num = CAb[ n + 1 ];
- nrg_b = CAb[ 0 ];
- nrg_f = CAf[ 0 ];
+ tmp1 = c[ n + 1 ];
+ num = 0.0f;
+ nrg = g[ 0 ];
for( k = 0; k < n; k++ ) {
- Atmp = Af[ k ];
- num += CAb[ n - k ] * Atmp;
- nrg_b += CAb[ k + 1 ] * Atmp;
- nrg_f += CAf[ k + 1 ] * Atmp;
+ atmp = a[ k ];
+ tmp1 += c[ n - k ] * atmp;
+ num += g[ n - k ] * atmp;
+ nrg += g[ k + 1 ] * atmp;
}
- silk_assert( nrg_f > 0.0 );
- silk_assert( nrg_b > 0.0 );
+ g[ n + 1] = tmp1;
+ num += tmp1;
+ silk_assert( nrg > 0.0 );
/* Calculate the next order reflection (parcor) coefficient */
- rc = -2.0 * num / ( nrg_f + nrg_b );
+ rc = -num / nrg;
silk_assert( rc > -1.0 && rc < 1.0 );
/* Update inverse prediction gain */
@@ -123,7 +129,7 @@ silk_float silk_burg_modified_FLP( /* O returns residual energy
/* Max prediction gain exceeded; set reflection coefficient such that max prediction gain is exactly hit */
rc = sqrt( 1.0 - minInvGain / invGain );
if( num > 0 ) {
- /* Ensure adjusted reflection coefficients has the original sign */
+ /* Ensure adjusted reflection coefficient has the original sign */
rc = -rc;
}
invGain = minInvGain;
@@ -134,53 +140,35 @@ silk_float silk_burg_modified_FLP( /* O returns residual energy
/* Update the AR coefficients */
for( k = 0; k < (n + 1) >> 1; k++ ) {
- tmp1 = Af[ k ];
- tmp2 = Af[ n - k - 1 ];
- Af[ k ] = tmp1 + rc * tmp2;
- Af[ n - k - 1 ] = tmp2 + rc * tmp1;
+ tmp1 = a[ k ];
+ tmp2 = a[ n - k - 1 ];
+ a[ k ] = tmp1 + rc * tmp2;
+ a[ n - k - 1 ] = tmp2 + rc * tmp1;
}
- Af[ n ] = rc;
+ a[ n ] = rc;
if( reached_max_gain ) {
/* Reached max prediction gain; set remaining coefficients to zero and exit loop */
for( k = n + 1; k < D; k++ ) {
- Af[ k ] = 0.0;
+ a[ k ] = 0.0;
}
break;
}
-
- /* Update C * Af and C * Ab */
- for( k = 0; k <= n + 1; k++ ) {
- tmp1 = CAf[ k ];
- CAf[ k ] += rc * CAb[ n - k + 1 ];
- CAb[ n - k + 1 ] += rc * tmp1;
- }
}
- if( reached_max_gain ) {
- /* Convert to silk_float */
- for( k = 0; k < D; k++ ) {
- A[ k ] = (silk_float)( -Af[ k ] );
- }
- /* Subtract energy of preceding samples from C0 */
- for( s = 0; s < nb_subfr; s++ ) {
- C0 -= silk_energy_FLP( x + s * subfr_length, D );
- }
- /* Approximate residual energy */
- nrg_f = C0 * invGain;
- } else {
- /* Compute residual energy and store coefficients as silk_float */
- nrg_f = CAf[ 0 ];
- tmp1 = 1.0;
- for( k = 0; k < D; k++ ) {
- Atmp = Af[ k ];
- nrg_f += CAf[ k + 1 ] * Atmp;
- tmp1 += Atmp * Atmp;
- A[ k ] = (silk_float)(-Atmp);
- }
- nrg_f -= FIND_LPC_COND_FAC * C0 * tmp1;
+ /* Convert to silk_float */
+ for( k = 0; k < D; k++ ) {
+ af[ k ] = (silk_float)( -a[ k ] );
+ }
+
+ nrg = c[ 0 ] * 0.5 * (1.0 - FIND_LPC_COND_FAC);
+ /* Subtract energy of preceding samples from C0 */
+ for( s = 0; s < nb_subfr; s++ ) {
+ nrg -= silk_energy_FLP( x + s * subfr_length, D );
}
+ /* Approximate residual energy */
+ nrg *= invGain;
- /* Return residual energy */
- return (silk_float)nrg_f;
+ /* Return approximate residual energy */
+ return (silk_float)nrg;
}
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