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/* ------------------------------------------------------------------
* Copyright (C) 1998-2009 PacketVideo
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied.
* See the License for the specific language governing permissions
* and limitations under the License.
* -------------------------------------------------------------------
*/
/*
Pathname: tns_ar_filter.c
------------------------------------------------------------------------------
REVISION HISTORY
Description: Modified from original shareware code
Description: Implemented 24-bit fixed point version
Optimized C code
Description:
- Added OVERFLOW_SHIFT_DOWN to avoid overflow.
- Increased precision by using the Q format of the LPC coefficient.
- Modified interface to add LPC Q format and scratch memory
for the state variables.
- Added pv_memset to clear state filter
- Updated format for comments (to PV standard)
- Updated copyright notice
Description:
- Changed multiplication scheme to increase precision. This
works better than older version.
Description:
- Include log2(order) as a scaling down parameter.
Description:
Modified to reflect code review comments
- misspelled words, extra comments and explicit requirements
Description:
deleted comment about fix Q format (L 107)
Description: Implemented a more efficient version, which eliminated the use
of "scratch memory" via introducing a pointer that references the actual
output.
Description: Removed the parameter "scratch_Int32_buffer" as this space
in memory is no longer needed by this function.
Description: Removed references to "scratch_Int32_buffer" in the Inputs
section.
Description:
Modified casting to ensure proper operations for different platforms
Description:
Per code review comment:
Eliminated casting to UInt and Int in b_low and b_high, they are
redundant and may add unncessary extra cycles in some platforms
Description: Updated the SW template to include the full pathname to the
source file and a slightly modified copyright header.
Description: Changed the order of the unsigned * signed multiply so the
casting to Int32 is performed on the unsigned operand.
Description:
Modified 32 by 16 bit multiplications to avoid unnecessary moves to
registers. Also split the code (based on flag direction) to simplify
pointer's updates
Description:
------------------------------------------------------------------------------
INPUT AND OUTPUT DEFINITIONS
Inputs:
spec = spectral input to be shaped by the filter.
Fixed point format
Int32[]
length = spec_length
spec_length = length of spec array.
const Int
direction = direction for application of tns filter.
+1 filters spectrum from low to high frequencies
(first input to filter is spec[0])
-1 filters spectrum from high to low frequencies
(first input to filter is spec[spec_length-1])
const Int
lpc = array of lpc coefficients, minus lpc[0] which is assumed to be "1"
Fixed point format
const Int[]
length = TNS_MAX_ORDER
Q_lpc = Q format for the lpc coeffcients (for max. precision, it assumes
that all 16 bits are used)
const Int
order = order of the TNS filter (Range of 1 - TNS_MAX_ORDER)
Int
Local Stores/Buffers/Pointers Needed:
None
Global Stores/Buffers/Pointers Needed:
None
Outputs:
None
Pointers and Buffers Modified:
spec = contains spectral data after application of TNS filter
Int32 array
length = spec_length
Local Stores Modified:
Global Stores Modified:
------------------------------------------------------------------------------
FUNCTION DESCRIPTION
A block of spectral data (Int32 spec[]) of length (const Int spec_length)
is processed by a simple all-pole filter defined by
LPC coefficients passed via (const Int lpc[])
TNS filter equation
y(n) = x(n) - lpc(2)*y(n-1) - ... - lpc(order+1)*y(n-order)
The filter calculation is performed in place, i.e. the output is passed
back to the calling function via (Int32 spec[])
The filter's order is defined by the variable (const Int order)
The direction of the filter's application is defined by (const Int inc)
------------------------------------------------------------------------------
REQUIREMENTS
This function should match the functionality of the ISO code.
The implementation does support filter orders bigger or equal to 1.
The size of the spectral coeffcients has to be bigger or equal than 1.
------------------------------------------------------------------------------
REFERENCES
(1) ISO/IEC 14496-3:1999(E)
Part 3
Subpart 4.6.8 (Temporal Noise Shaping)
(2) MPEG-2 NBC Audio Decoder
"This software module was originally developed by AT&T, Dolby
Laboratories, Fraunhofer Gesellschaft IIS in the course of development
of the MPEG-2 NBC/MPEG-4 Audio standard ISO/IEC 13818-7, 14496-1,2 and
3. This software module is an implementation of a part of one or more
MPEG-2 NBC/MPEG-4 Audio tools as specified by the MPEG-2 NBC/MPEG-4
Audio standard. ISO/IEC gives users of the MPEG-2 NBC/MPEG-4 Audio
standards free license to this software module or modifications thereof
for use in hardware or software products claiming conformance to the
MPEG-2 NBC/MPEG-4 Audio standards. Those intending to use this software
module in hardware or software products are advised that this use may
infringe existing patents. The original developer of this software
module and his/her company, the subsequent editors and their companies,
and ISO/IEC have no liability for use of this software module or
modifications thereof in an implementation. Copyright is not released
for non MPEG-2 NBC/MPEG-4 Audio conforming products.The original
developer retains full right to use the code for his/her own purpose,
assign or donate the code to a third party and to inhibit third party
from using the code for non MPEG-2 NBC/MPEG-4 Audio conforming products.
This copyright notice must be included in all copies or derivative
works."
Copyright(c)1996.
------------------------------------------------------------------------------
PSEUDO-CODE
FOR (i=0; i<order; i++)
state[i] = 0;
ENDFOR
IF (inc == -1)
THEN
spec = spec + spec_length - 1;
ENDIF
FOR (i=0; i<spec_length; i++)
y = *spec;
FOR (j=0; j<order; j++)
y -= lpc[j] * state[j];
ENDFOR
FOR (j=order-1; j>0; j--)
state[j] = state[j-1];
ENDFOR
state[0] = y;
*spec = y;
spec = spec + inc;
ENDFOR
------------------------------------------------------------------------------
RESOURCES USED
When the code is written for a specific target processor
the resources used should be documented below.
STACK USAGE: [stack count for this module] + [variable to represent
stack usage for each subroutine called]
where: [stack usage variable] = stack usage for [subroutine
name] (see [filename].ext)
DATA MEMORY USED: x words
PROGRAM MEMORY USED: x words
CLOCK CYCLES: [cycle count equation for this module] + [variable
used to represent cycle count for each subroutine
called]
where: [cycle count variable] = cycle count for [subroutine
name] (see [filename].ext)
------------------------------------------------------------------------------
*/
/*----------------------------------------------------------------------------
; INCLUDES
----------------------------------------------------------------------------*/
#include "pv_audio_type_defs.h"
#include "e_tns_const.h"
#include "tns_ar_filter.h"
#include "fxp_mul32.h"
/*----------------------------------------------------------------------------
; MACROS
; Define module specific macros here
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; DEFINES
; Include all pre-processor statements here. Include conditional
; compile variables also.
----------------------------------------------------------------------------*/
#define MASK_LOW16 0xFFFF
#define UPPER16 16
/*----------------------------------------------------------------------------
; LOCAL FUNCTION DEFINITIONS
; Function Prototype declaration
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL STORE/BUFFER/POINTER DEFINITIONS
; Variable declaration - defined here and used outside this module
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; EXTERNAL FUNCTION REFERENCES
; Declare functions defined elsewhere and referenced in this module
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES
; Declare variables used in this module but defined elsewhere
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; FUNCTION CODE
----------------------------------------------------------------------------*/
Int tns_ar_filter(
Int32 spec[],
const Int spec_length,
const Int direction,
const Int32 lpc[],
const Int Q_lpc,
const Int order)
{
Int i;
Int j;
/*
* Multiplication related variables
*/
Int32 temp;
/*
* Filter related variables
*/
Int32 y0;
/*
* Circular buffer to hold the filter's state
* (y[n-1],y[n-2],y[n-3],etc.)
*
* p_state and p_lpc should take advantage
* of any special circular buffer instructions
* if this code is hand-optimized in assembly.
*/
Int32 *p_state = NULL;
const Int32 *p_lpc;
Int shift_up;
Int shift_down_amount;
/*
* Pointer to the I/O memory space
*/
Int32 *p_spec = spec;
i = 0;
j = order;
/*
* get the power of 2 that is bigger than the order
* i is the bit counter and j is modified until exceed
* the power of 2 corresponding to TNS_MAX_ORDER
*/
while (j < 0x010)
{
j <<= 1;
i++;
}
/*
* 5 is the number of bits needed to represent 0x010
* TNS_MAX_ORDER = 20, power of 2 that include 20 is 5
*/
shift_down_amount = 4 - i;
shift_up = UPPER16 - Q_lpc;
/*
* shift_down_amount == power of 2 that is bigger than the order - 1
*/
shift_down_amount += shift_up;
if (direction == -1)
{
p_spec += spec_length - 1;
for (i = order; i != 0; i--)
{
y0 = *p_spec >> shift_down_amount;
p_lpc = lpc;
/* 32 by 32 bit multiplication */
for (j = order; j > i; j--)
{
temp = *p_state++;
y0 -= fxp_mul32_Q31(temp, *(p_lpc++)) << shift_up;
}
/*
* Record the output in-place
*/
p_state = p_spec;
*(p_spec--) = y0;
}
if (spec_length > order)
{
for (i = (spec_length - order); i != 0; i--)
{
y0 = *p_spec >> shift_down_amount;
p_lpc = &(lpc[0]);
/* 32 by 32 bit multiplication */
for (j = order; j != 0; j--)
{
temp = *p_state++;
y0 -= fxp_mul32_Q31(temp, *(p_lpc++)) << shift_up;
}
/*
* Record the output in-place
*/
p_state = p_spec;
*(p_spec--) = y0;
} /* END for (i = (spec_length - order); i>0; i--) */
}
}
else
{
for (i = order; i != 0; i--)
{
p_lpc = lpc;
y0 = 0;
/* 32 by 32 bit multiplication */
for (j = order; j > i; j--)
{
y0 -= fxp_mul32_Q31(*p_state--, *(p_lpc++));
}
p_state = p_spec;
/*
* Record the output in-place
*/
*(p_spec) = (*p_spec >> shift_down_amount) + (y0 << shift_up);
p_spec++;
}
if (spec_length > order)
{
for (i = (spec_length - order); i != 0; i--)
{
p_lpc = lpc;
y0 = 0;
/* 32 by 32 bit multiplication */
for (j = order; j != 0; j--)
{
y0 -= fxp_mul32_Q31(*p_state--, *(p_lpc++));
}
p_state = p_spec;
/*
* Record the output in-place
*/
*(p_spec) = (*p_spec >> shift_down_amount) + (y0 << shift_up);
p_spec++;
} /* END for (i = (spec_length - order); i>0; i--) */
}
}
return(shift_down_amount);
} /* tns_ar_filter */
|