/* ------------------------------------------------------------------ * 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< 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 */