VLCDecodeEscBlock_MP3

Syntax

Parameters

Description

The function ippsVLCDecodeEscBlock_MP3is declared in the ippac.h header file. The function parses the bitstream and decodes variable length code using the VLCDecoder specification structure built by the function ippsVLCDecodeInit_32s or ippsVLCDecodeInitAlloc_32s from data compression domain, and resets the pointers to new positions. The pointer pBitStream points to the 8-bit value and the bit offset may vary from one to 32. After processing, the pointer and bit offset are changed and their new values are returned. To use the function ippsVLCDecodeEscBlock_MP3, rearrange inputTable before initialization as follows:

value = (first_sample_value) << 8) + (second_sample_value + 128).

code = (((code_ini << (first_sample_value != 0)) + (first_sample_value < 0)) << (second_sample_value != 0)) + (first_sample_value < 0).

length = length_ini + (first_sample_value != 0) + (second_sample_value != 0).

MP3Esc VLC codebook is an unsigned two-dimensional codebook with a large absolute value equal to 15.

From one record of the initial inputTable you can obtain from one to four records of rearranged inputTable. For example:

abs(first_sample_value)  = 9;
abs(second_sample_value) = 6;

code_ini = 0xf5
length_ini = 12;

record 1: first_sample_value = -9, second_sample_value = -6;
		value = (-9 << 8) + (-6 + 128) = -2182;
		code = (((0xf5 << 1) + 1) << 1) + 1 = 0x3d7;
		length = 12 + 1 + 1 = 14;
		{-2182, 0x3d7, 14)

record 2: first_sample_value = -9, second_sample_value = 6;
		value = (-9 << 8) + (6 + 128) = -2170;
		code = (((0xf5 << 1) + 1) << 1) + 0 = 0x3d6;
		length = 12 + 1 + 1 = 14;
		-2170, 0x3d6, 14)

record 3: first_sample_value = 9, second_sample_value = -6;
		value = (9 << 8) + (-6 + 128) = 2426;
		code = (((0xf5 << 1) + 0) << 1) + 1 = 0x3d5;
		length = 12 + 1 + 1 = 14;
		{2426, 0x3d7, 14)

record 4: first_sample_value = 9,
second_sample_value = 6;
		value = (9 << 8) + (6 + 128) = 2438;
		code = (((0xf5 << 1) + 0) << 1) + 0 = 0x3d4;
		length = 12 + 1 + 1 = 14;
		{2438, 0x3d7, 14)

The function ippsVLCDecodeEscBlock_MP3_1u16s is used in the float-point and fixed-point versions of MP3 decoder included into IPP Samples. See introduction to this section.

Return Values