| /* ------------------------------------------------------------------ |
| * 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: ./src/huffcb.c |
| Funtions: |
| huffcb |
| |
| |
| ------------------------------------------------------------------------------ |
| REVISION HISTORY |
| |
| Description: Modified from original shareware code |
| |
| Description: Modified to pass variables by reference to eliminate use |
| of global variables. |
| |
| Description: Change variable names for clarity, |
| change variables 'base', 'sect_len_inc', and 'esc_val' to |
| UChar type. |
| |
| Description: Add "if ((pSect[-1] % sfb_per_win) > max_sfb)" statement to |
| detect the error condition. |
| add more white space. |
| |
| Description: eliminated "pSect[-1]%sfb_per_win" operation |
| |
| Description: eliminated "pSect[-1]%sfb_per_win" operation |
| |
| Description: (1) Pass in SectInfo pSect |
| (2) put BITS *pInputStream as second parameter |
| |
| Description: Fix a failure for thrid party AAC encoding. |
| The problem came when the total and the |
| maximun number of active scale factor bands do not coincide. |
| This is a rare situation but produces a problem when decoding |
| encoders that tolerate this. |
| |
| Description: Replace some instances of getbits to get9_n_lessbits |
| when the number of bits read is 9 or less and get1bits |
| when only 1 bit is read. |
| |
| Description: |
| |
| ------------------------------------------------------------------------------ |
| INPUT AND OUTPUT DEFINITIONS |
| |
| Inputs: |
| |
| UChar *pSect = pointer to array that contains the interleaved |
| information of huffman codebook index and section |
| length. Array contains: |
| [codebook index] |
| [section boundary] |
| [codebook index] |
| [section boundary] |
| ... |
| |
| Int sectbits = array that defines the number of bits |
| used for expressing the escape value of |
| section length |
| |
| Int tot_sfb = total number of sfb in one Frame |
| |
| Int sfb_per_win = number of sfb in each sub-block (window) |
| |
| UChar max_sfb = 1 + number of active sfbs - see reference (2) p56 |
| |
| BITS *pInputStream = pointer to input stream |
| |
| |
| Local Stores/Buffers/Pointers Needed: |
| |
| UChar base = number of sfb in already detected sections |
| |
| UChar sect_len_inc = section length increment in number of sfbs' |
| |
| UChar esc_val = escape value for section length |
| |
| Int bits = number of bits needed for expressing section length |
| |
| |
| Global Stores/Buffers/Pointers Needed: |
| |
| |
| Outputs: |
| |
| num_sect = total number of sections in one frame |
| |
| |
| Pointers and Buffers Modified: |
| |
| UChar *pSect = pointer to array where huffman codebook index and |
| section length are stored |
| |
| Local Stores Modified: |
| |
| Global Stores Modified: |
| |
| ------------------------------------------------------------------------------ |
| FUNCTION DESCRIPTION |
| |
| Background knowledge: 1024(960) coef's are separated into several sections, |
| each section is encoded with one single Huffman codebook, and each section |
| has a length of multiples of sfb. |
| |
| max_sfb <= sfb_per_win <= tot_sfb |
| tot_sfb = total number of scalefactor bands in one frame (1024 coefs) |
| |
| This function reads the codebook index and section boundaries (expressed |
| in number of sfb) from the input bitstream, store these information in |
| *pSect, and return the number of sections been detected. Returns 0 if there |
| is an error. |
| |
| ------------------------------------------------------------------------------ |
| REQUIREMENTS |
| |
| This function should fill the array *pSect with section Huffman codebook |
| indexes and section boundaries |
| |
| ------------------------------------------------------------------------------ |
| REFERENCES |
| |
| (1) 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. |
| |
| (2) ISO/IEC 14496-3 1999(E) |
| Subpart 4 p55 (Recovering section_data()) |
| p24-25 (Syntax of section_data()) |
| |
| (3) M. Bosi, K. Brandenburg, etc., "ISO/IEC MPEG-2 Advanced Audio Coding," |
| J. Audio Eng. Soc., Vol.45, No.10, 1997 October |
| |
| ------------------------------------------------------------------------------ |
| PSEUDO-CODE |
| |
| bits_needed_for_ESC = sectbits[0]; |
| ESC_value = (1<<bits_needed_for_ESC) - 1; |
| num_of_section = 0; |
| |
| |
| FOR (base = 0; base<total_sfb AND num_of_section<total_sfb) |
| { |
| *pSect++ = getbits(LEN_CB, pInputStream); (read huffman_codebook_num) |
| sect_length_incr = getbits(bits_needed_for_ESC, pInputStream); |
| |
| WHILE (sect_length_incr == ESC_value AND base < total_sfb) |
| { |
| base += ESC_value; |
| sect_length_incr = getbits(bits_needed_for_ESC, ebits); |
| } |
| ENDWHILE |
| |
| base += sect_length_incr; |
| *pSect++ = base; |
| num_of_section++; |
| |
| IF (num_of_sfb_for_this_group==max_sfb) |
| { |
| *pSect++ = 0; (use huffman codebook 0) |
| base += sfb_per_win - max_sfb; |
| *pSect++ = base; |
| num_of_section++; |
| } |
| ENDIF |
| |
| IF (num_of_sfb_for_this_group > max_sfb) |
| break; |
| ENDIF |
| |
| } |
| ENDFOR |
| |
| IF (base != total_sfb OR num_of_section>total_sfb) |
| return 0; |
| ENDIF |
| |
| return num_sect; |
| |
| ------------------------------------------------------------------------------ |
| RESOURCES USED |
| When the code is written for a specific target processor the |
| 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 "huffman.h" |
| |
| /*---------------------------------------------------------------------------- |
| ; MACROS |
| ; Define module specific macros here |
| ----------------------------------------------------------------------------*/ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; DEFINES |
| ; Include all pre-processor statements here. Include conditional |
| ; compile variables also. |
| ----------------------------------------------------------------------------*/ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; 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 huffcb( |
| SectInfo *pSect, |
| BITS *pInputStream, |
| Int sectbits[], |
| Int tot_sfb, |
| Int sfb_per_win, |
| Int max_sfb) |
| { |
| /*---------------------------------------------------------------------------- |
| ; Define all local variables |
| ----------------------------------------------------------------------------*/ |
| |
| Int base; /* section boundary */ |
| Int sect_len_incr; |
| Int esc_val; /* ESC of section length = 31(long), =7 (short) */ |
| Int bits; /* # of bits used to express esc_val */ |
| Int num_sect; |
| Int active_sfb; |
| Int group_base; |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; Function body here |
| ----------------------------------------------------------------------------*/ |
| |
| bits = sectbits[0]; /* 3 for SHORT_WIN, 5 for LONG_WIN */ |
| esc_val = (1 << bits) - 1; /* ESC_value for section length */ |
| num_sect = 0; |
| base = 0; |
| group_base = 0; |
| |
| /* read until the end of one frame */ |
| while ((base < tot_sfb) && (num_sect < tot_sfb)) |
| { |
| |
| pSect->sect_cb = get9_n_lessbits( |
| LEN_CB, |
| pInputStream); /* section codebook */ |
| |
| sect_len_incr = get9_n_lessbits( |
| bits, |
| pInputStream); /* length_incr */ |
| |
| |
| /* read until non-ESC value, see p55 reference 2 */ |
| while ((sect_len_incr == esc_val) && (base < tot_sfb)) |
| { |
| base += esc_val; |
| |
| sect_len_incr = get9_n_lessbits( |
| bits, |
| pInputStream); |
| } |
| |
| base += sect_len_incr; |
| pSect->sect_end = base; /* total # of sfb until current section */ |
| pSect++; |
| num_sect++; |
| |
| /* active_sfb = base % sfb_per_win; */ |
| active_sfb = base - group_base; |
| |
| /* |
| * insert a zero section for regions above max_sfb for each group |
| * Make sure that active_sfb is also lesser than tot_sfb |
| */ |
| |
| if ((active_sfb == max_sfb) && (active_sfb < tot_sfb)) |
| { |
| base += (sfb_per_win - max_sfb); |
| pSect->sect_cb = 0; /* huffman codebook 0 */ |
| pSect->sect_end = base; |
| num_sect++; |
| pSect++; |
| group_base = base; |
| } |
| else if (active_sfb > max_sfb) |
| { |
| /* within each group, the sections must delineate the sfb |
| * from zero to max_sfb so that the 1st section within each |
| * group starts at sfb0 and the last section ends at max_sfb |
| * see p55 reference 2 |
| */ |
| break; |
| } |
| |
| } /* while (base=0) */ |
| |
| |
| if (base != tot_sfb || num_sect > tot_sfb) |
| { |
| num_sect = 0; /* error */ |
| } |
| |
| return num_sect; |
| |
| } /* huffcb */ |
| |
| |
