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Josh Coalson
142
src/libFLAC/include/private/lpc.h
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142
src/libFLAC/include/private/lpc.h
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/* libFLAC - Free Lossless Audio Coder library
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* Copyright (C) 2000 Josh Coalson
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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#ifndef FLAC__PRIVATE__LPC_H
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#define FLAC__PRIVATE__LPC_H
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#include "FLAC/ordinals.h"
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#define FLAC__MAX_LPC_ORDER (32u)
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/*
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* FLAC__lpc_compute_autocorrelation()
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* --------------------------------------------------------------------
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* Compute the autocorrelation for lags between 0 and lag-1.
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* Assumes data[] outside of [0,data_len-1] == 0.
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* Asserts that lag > 0.
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*
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* IN data[0,data_len-1]
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* IN data_len
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* IN 0 < lag <= data_len
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* OUT autoc[0,lag-1]
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*/
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void FLAC__lpc_compute_autocorrelation(const real data[], unsigned data_len, unsigned lag, real autoc[]);
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/*
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* FLAC__lpc_compute_lp_coefficients()
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* --------------------------------------------------------------------
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* Computes LP coefficients for orders 1..max_order.
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* Do not call if autoc[0] == 0.0. This means the signal is zero
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* and there is no point in calculating a predictor.
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*
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* IN autoc[0,max_order] autocorrelation values
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* IN 0 < max_order <= FLAC__MAX_LPC_ORDER max LP order to compute
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* OUT lp_coeff[0,max_order-1][0,max_order-1] LP coefficients for each order
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* *** IMPORTANT:
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* *** lp_coeff[0,max_order-1][max_order,FLAC__MAX_LPC_ORDER-1] are untouched
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* OUT error[0,max_order-1] error for each order
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*
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* Example: if max_order is 9, the LP coefficients for order 9 will be
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* in lp_coeff[8][0,8], the LP coefficients for order 8 will be
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* in lp_coeff[7][0,7], etc.
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*/
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void FLAC__lpc_compute_lp_coefficients(const real autoc[], unsigned max_order, real lp_coeff[][FLAC__MAX_LPC_ORDER], real error[]);
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/*
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* FLAC__lpc_quantize_coefficients()
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* --------------------------------------------------------------------
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* Quantizes the LP coefficients. NOTE: precision + bits_per_sample
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* must be less than 32 (sizeof(int32)*8).
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*
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* IN lp_coeff[0,order-1] LP coefficients
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* IN order LP order
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* IN FLAC__MIN_QLP_COEFF_PRECISION < precision
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* desired precision (in bits, including sign
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* bit) of largest coefficient
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* IN bits_per_sample > 0 bits per sample of the originial signal
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* OUT qlp_coeff[0,order-1] quantized coefficients
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* OUT bits # of bits to shift right to get approximated
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* LP coefficients. NOTE: could be negative,
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* but |*bits| will always be <= precision
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* RETURN 0 => quantization OK
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* 1 => coefficients vary too much to quantize to the desired
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* precision. 'bits' is unset
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* 2 => coefficients are all zero, which is bad. 'bits' is unset
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*/
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int FLAC__lpc_quantize_coefficients(const real lp_coeff[], unsigned order, unsigned precision, unsigned bits_per_sample, int32 qlp_coeff[], int *bits);
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/*
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* FLAC__lpc_compute_residual_from_qlp_coefficients()
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* --------------------------------------------------------------------
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* Compute the residual signal obtained from sutracting the predicted
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* signal from the original.
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*
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* IN data[-order,data_len-1] original signal (NOTE THE INDICES!)
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* IN data_len length of original signal
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* IN qlp_coeff[0,order-1] quantized LP coefficients
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* IN order > 0 LP order
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* IN lp_quantization quantization of LP coefficients in bits
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* OUT residual[0,data_len-1] residual signal
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*/
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void FLAC__lpc_compute_residual_from_qlp_coefficients(const int32 data[], unsigned data_len, const int32 qlp_coeff[], unsigned order, int lp_quantization, int32 residual[]);
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/*
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* FLAC__lpc_restore_signal()
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* --------------------------------------------------------------------
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* Restore the original signal by summing the residual and the
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* predictor.
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*
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* IN residual[0,data_len-1] residual signal
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* IN data_len length of original signal
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* IN qlp_coeff[0,order-1] quantized LP coefficients
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* IN order > 0 LP order
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* IN lp_quantization quantization of LP coefficients in bits
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* *** IMPORTANT: the caller must pass in the historical samples:
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* IN data[-order,-1] previously-reconstructed historical samples
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* OUT data[0,data_len-1] original signal
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*/
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void FLAC__lpc_restore_signal(const int32 residual[], unsigned data_len, const int32 qlp_coeff[], unsigned order, int lp_quantization, int32 data[]);
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/*
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* FLAC__lpc_compute_expected_bits_per_residual_sample()
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* --------------------------------------------------------------------
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* Compute the expected number of bits per residual signal sample
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* based on the LP error (which is related to the residual variance).
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*
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* IN lpc_error >= 0.0 error returned from calculating LP coefficients
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* IN total_samples > 0 # of samples in residual signal
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* RETURN expected bits per sample
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*/
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real FLAC__lpc_compute_expected_bits_per_residual_sample(real lpc_error, unsigned total_samples);
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/*
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* FLAC__lpc_compute_best_order()
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* --------------------------------------------------------------------
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* Compute the best order from the array of signal errors returned
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* during coefficient computation.
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*
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* IN lpc_error[0,max_order-1] >= 0.0 error returned from calculating LP coefficients
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* IN max_order > 0 max LP order
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* IN total_samples > 0 # of samples in residual signal
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* IN bits_per_signal_sample # of bits per sample in the original signal
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* RETURN [1,max_order] best order
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*/
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unsigned FLAC__lpc_compute_best_order(const real lpc_error[], unsigned max_order, unsigned total_samples, unsigned bits_per_signal_sample);
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#endif
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