A DSP-based decompressor unit for high-fidelity MPEG-Audio over TCP/IP networks

Copyright 1997 by Björn Wesén at Axis Communications AB, Sweden

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Appendix D - The main C sourcecode

The program was written with some object-orientation in mind, which means that all functions that operate on a certain structure, has the structure's name as prefix in the function name, for example "Bitstream_get" which gets bits from a bitstream structure.

There is a sea of conditional compile directives in the source, because of its multi-platform compiling. It was designed to be compileable on both Linux, Windows and the DSP of course. As a result, it can be quite difficult to browse some parts of the code without looking closer. The code was optimized for realtime playback on a DSP, not for readability or expandability.

The following files constitute the main C sourcecode. The tablefiles are omitted.

• mp3dec.h - The main header file defining the structures and functions in the decoder
• mp3dec.c - The main source file, including the main loop and most decoding functions
• huff.c - The huffman decoder (speed-up ideas in this were borrowed from Amp by Tomislav Uzelac)
• fastimdct.c - The optimized IMDCT transform
• fastsb.c - The optimized "polyphase subband transform", really another IMDCT
• windowing.c - The output filtering function

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