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Diffstat (limited to 'media/libstagefright/codecs/aacdec/tns_ar_filter.cpp')
| -rw-r--r-- | media/libstagefright/codecs/aacdec/tns_ar_filter.cpp | 474 |
1 files changed, 474 insertions, 0 deletions
diff --git a/media/libstagefright/codecs/aacdec/tns_ar_filter.cpp b/media/libstagefright/codecs/aacdec/tns_ar_filter.cpp new file mode 100644 index 0000000..db31a63 --- /dev/null +++ b/media/libstagefright/codecs/aacdec/tns_ar_filter.cpp @@ -0,0 +1,474 @@ +/* ------------------------------------------------------------------ + * 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 */ |