VLC decoding tables

Functions
static bool	ojph::local::uvlc_init_tables ()
	Initializes uvlc_tbl0 and uvlc_tbl1 tables.
static bool	ojph::local::uvlc_init_wide_table ()
	Initializes uvlc_tbl1_wide: wider UVLC table for non-initial rows. Index = mode(2b) * 1024 + vlc(10b). Entry packs total_bits[4:0], u_q0[12:5], u_q1[20:13]. total_bits == 0x1F signals fallback to original decode.

Variables
ui16	ojph::local::uvlc_tbl0 [256+64] = { 0 }
	uvlc_tbl0 contains decoding information for initial row of quads
ui16	ojph::local::uvlc_tbl1 [256] = { 0 }
	uvlc_tbl1 contains decoding information for non-initial row of quads
ui32	ojph::local::uvlc_tbl1_wide [4096] = { 0 }
	uvlc_tbl1_wide: wider UVLC table for non-initial rows. Index = mode(2 bits) * 1024 + vlc_data(10 bits) = 12 bits. Entry bits: [4:0]=total_bits, [12:5]=u_q0, [20:13]=u_q1. total_bits == 0x1F means fallback to original decode path.
ui8	ojph::local::uvlc_bias [256+64] = { 0 }
	uvlc_bias contains decoding info. for initial row of quads
static bool	ojph::local::uvlc_tables_initialized = uvlc_init_tables()
	Initializes UVLC tables uvlc_tbl0 and uvlc_tbl1.
static bool	ojph::local::uvlc_wide_initialized = uvlc_init_wide_table()
	Initializes wide UVLC table uvlc_tbl1_wide.

Detailed Description

UVLC decoding tables used to partially decode u values from UVLC
codewords.
The table index is 8 (or 9) bits and composed of two parts:
The 6 LSBs carries the head of the VLC to be decoded. Up to 6 bits to be used; these are uvlc prefix code for quad 0 and 1
The 2 (or 3) MSBs contain u_off of quad 0 + 2 * o_off quad 1

• 4 * mel event for initial row of quads when needed
  
  Each entry contains, starting from the LSB
  
  • total total prefix length for quads 0 and 1 (3 bits)
    
  • total total suffix length for quads 0 and 1 (4 bits)
    
  • suffix length for quad 0 (3 bits)
    
  • prefix for quad 0 (3 bits)
    
  • prefix for quad 1 (3 bits)
    
    Another table is uvlc_bias, which is needed to correctly decode the extension u_ext for initial row of quads. Under certain condition, we deduct 1 or 2 from u_q0 and u_q1 before encoding them; so for us to know that decoding u_ext is needed, we recreate the u_q0 and u_q1 that we actually encoded.
    For simplicity, we use the same index as before
    
  • u_q0 bias is 2 bits
    
  • u_q1 bias is 2 bits
    

Function Documentation

uvlc_init_tables()

bool ojph::local::uvlc_init_tables ( )

static

#include <ojph_block_common.cpp>

Initializes uvlc_tbl0 and uvlc_tbl1 tables.

Definition at line 196 of file ojph_block_common.cpp.

References uvlc_bias, uvlc_tbl0, and uvlc_tbl1.

Referenced by initialize_block_encoder_tables().

uvlc_init_wide_table()

bool ojph::local::uvlc_init_wide_table ( )

static

#include <ojph_block_common.cpp>

Initializes uvlc_tbl1_wide: wider UVLC table for non-initial rows. Index = mode(2b) * 1024 + vlc(10b). Entry packs total_bits[4:0], u_q0[12:5], u_q1[20:13]. total_bits == 0x1F signals fallback to original decode.

Definition at line 346 of file ojph_block_common.cpp.

References uvlc_tbl1_wide.

Variable Documentation

uvlc_bias

ui8 ojph::local::uvlc_bias = { 0 }

#include <ojph_block_common.cpp>

uvlc_bias contains decoding info. for initial row of quads

Definition at line 116 of file ojph_block_common.cpp.

Referenced by ojph_decode_codeblock64(), and uvlc_init_tables().

uvlc_tables_initialized

bool ojph::local::uvlc_tables_initialized = uvlc_init_tables()

static

#include <ojph_block_common.cpp>

Initializes UVLC tables uvlc_tbl0 and uvlc_tbl1.

Definition at line 428 of file ojph_block_common.cpp.

uvlc_tbl0

ui16 ojph::local::uvlc_tbl0 = { 0 }

#include <ojph_block_common.cpp>

uvlc_tbl0 contains decoding information for initial row of quads

Definition at line 106 of file ojph_block_common.cpp.

Referenced by ojph_decode_codeblock32(), ojph_decode_codeblock64(), ojph_decode_codeblock_wasm(), and uvlc_init_tables().

uvlc_tbl1

ui16 ojph::local::uvlc_tbl1 = { 0 }

#include <ojph_block_common.cpp>

uvlc_tbl1 contains decoding information for non-initial row of quads

Definition at line 109 of file ojph_block_common.cpp.

Referenced by ojph_decode_codeblock32(), ojph_decode_codeblock64(), ojph_decode_codeblock_wasm(), and uvlc_init_tables().

uvlc_tbl1_wide

ui32 ojph::local::uvlc_tbl1_wide = { 0 }

#include <ojph_block_common.cpp>

uvlc_tbl1_wide: wider UVLC table for non-initial rows. Index = mode(2 bits) * 1024 + vlc_data(10 bits) = 12 bits. Entry bits: [4:0]=total_bits, [12:5]=u_q0, [20:13]=u_q1. total_bits == 0x1F means fallback to original decode path.

Definition at line 114 of file ojph_block_common.cpp.

Referenced by uvlc_init_wide_table().

uvlc_wide_initialized

bool ojph::local::uvlc_wide_initialized = uvlc_init_wide_table()

static

#include <ojph_block_common.cpp>

Initializes wide UVLC table uvlc_tbl1_wide.

Definition at line 434 of file ojph_block_common.cpp.