81 lines
3.1 KiB
Text
81 lines
3.1 KiB
Text
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Library: Reverse-engineered ALAC decoder v0.1.0
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Imported: 2005-08-14 by Dave Chapman
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This directory contains a local version of an ALAC (Apple Lossless Audio
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Codec) for use by Rockbox for software decoding of ALAC files. It is
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based on the reverse-engineered decoder by David Hamilton.
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LICENSING INFORMATION
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/*
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* ALAC (Apple Lossless Audio Codec) decoder
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* Copyright (c) 2005 David Hammerton
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* All rights reserved.
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*
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* This is the actual decoder.
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*
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* http://crazney.net/programs/itunes/alac.html
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or
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* sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*
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*/
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IMPORT DETAILS
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The base version first imported into Rockbox was the first release
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(v0.1.0) of the ALAC decoder by David Hammerton.
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Only the files alac.[ch], demux.[ch] and stream.h were used.
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stream.c (the original FILE* based I/O implementation) was replaced with
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functions in the ALAC codec - to interface with the Rockbox audio playback
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system.
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References to <stdint.h> were replaced with <inttypes.h> and debugging
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calls to fprintf were removed.
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The ALAC decoder itself was modified to return samples in host-endian
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order, instead of little-endian.
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The run-time detection of CPU endianness was replaced with
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compile-time tests of the ROCKBOX_LITTLE_ENDIAN define.
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All malloc calls were removed from alac.c, but some are still present
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in the metadata parser in demux.c - to store unbounded data such as
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the size in bytes of each compressed block in the file.
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The only changes to demux.c were to remove debugging calls to fprintf.
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The most-used buffers (the temporary 32-bit output buffer) were moved
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into IRAM (on the iRiver). This was enough to make the decoder work
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in real-time.
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A point of interest - the -O3 gcc option (the setting used in the
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original Makefile provided with the alac decoder) gives a significant
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speedup compared to -O2. With -O2, the Coldfire runs at a constant
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120MHz, but with -O3, it can power-down to 40MHz for a small amount of
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time.
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The file alac.c contained some hints from the original author for
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places where major optimisations can be made - specifically the
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unrolling and optimisation of certain cases of general loops.
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