121 lines
4.6 KiB
Plaintext
121 lines
4.6 KiB
Plaintext
COPYRIGHT
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This package is copyright 2006 by Phil Karn, KA9Q. It may be used
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under the terms of the GNU Lesser General Public License (LGPL). See
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the file "lesser.txt" in this package for license details.
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INTRODUCTION
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This package provides a set of functions that implement several
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popular forward error correction (FEC) algorithms and several low-level routines
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useful in modems implemented with digital signal processing (DSP).
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The following routines are provided:
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1. Viterbi decoders for the following convolutional codes:
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r=1/2 k=7 ("Voyager" code, now a widely used industry standard)
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r=1/2 k=9 (Used on the IS-95 CDMA forward link)
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r=1/6 k=15 ("Cassini" code, used by several NASA/JPL deep space missions)
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2. Reed-Solomon encoders and decoders for any user-specified code.
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3. Optimized encoder and decoder for the CCSDS-standard (255,223)
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Reed-Solomon code, with and without the CCSDS-standard "dual basis"
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symbol representation.
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4. Compute dot product between a 16-bit buffer and a set of 16-bit
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coefficients. This is the basic DSP primitive for digital filtering
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and correlation.
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4. Compute sum of squares of a buffer of 16-bit signed integers. This is
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useful in DSP for finding the total energy in a signal.
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5. Find peak value in a buffer of 16-bit signed integers, useful for
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scaling a signal to prevent overflow.
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SIMD SUPPORT
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This package automatically makes use of various SIMD (Single
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Instruction stream, Multiple Data stream) instruction sets, when
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available: MMX, SSE and SSE2 on the IA-32 (Intel) architecture, and
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Altivec on the PowerPC G4 and G5 used by Power Macintoshes.
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"Altivec" is a Motorola trademark; Apple calls it "Velocity Engine",
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and IBM calls it "VMX". Altivec is roughly comparable to SSE2 on the
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IA-32.
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Many of the SIMD versions run more than an order of
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magnitude faster than their portable C versions. The available SIMD
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instruction sets, if any, are determined at run time and the proper
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version of each routine is automatically selected. If no SIMD
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instructions are available, the portable C version is invoked by
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default. On targets other than IA-32 and PPC, only the portable C
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version is built.
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The SIMD-assisted versions generally produce the same results as the C
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versions, with a few minor exceptions. The Viterbi decoders in C have
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a very slightly greater Eb/No performance due to their use of 32-bit
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path metrics. On the other hand, the SIMD versions use the
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"saturating" arithmetic available in these instructions to avoid the
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integer wraparounds that can occur in C when argument ranges are not
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properly constrained. This applies primarily to the "dotprod" (dot
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product) function.
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The MMX (MultiMedia eXtensions) instruction set was introduced on
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later Pentium CPUs; it is also implemented on the Pentium II and most
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AMD CPUs starting with the K6. SSE (SIMD Streaming Extensions) was
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introduced in the Pentium III; AMD calls it "3D Now! Professional".
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Intel introduced SSE2 on the Pentium 4, and it has been picked up by
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later AMD CPUs. SSE support implies MMX support, while SSE2 support
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implies both SSE and MMX support.
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The latest IA-32 SIMD instruction set, SSE3 (also known as "Prescott
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New Instructions") was introduced in early 2004 with the latest
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("Prescott") revision of the Pentium 4. Relatively little was
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introduced with SSE3, and this library currently makes no use of it.
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See the various manual pages for details on how to use the library
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routines.
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Copyright 2006, Phil Karn, KA9Q
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karn@ka9q.net
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http://www.ka9q.net/
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This software may be used under the terms of the GNU Lesser General
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Public License (LGPL); see the file lesser.txt for details.
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Revision history:
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Version 1.0 released 29 May 2001
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Version 2.0 released 3 Dec 2001:
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Restructured to add support for shared libraries.
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Version 2.0.1 released 8 Dec 2001:
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Includes autoconf/configure script
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Version 2.0.2 released 4 Feb 2002:
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Add SIMD version override options
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Test for lack of SSE2 mnemonic support in 'as'
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Build only selected version
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Version 2.0.3 released 6 Feb 2002:
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Fix to parityb function in parity.h
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feclib version 1.0 released November 2003
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Merged SIMD-Viterbi, RS and DSP libraries
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Changed SIMD Viterbi decoder to detect SSE2/SSE/MMX at runtime rather than build time
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feclib version 2.0 (unreleased) Mar 2004
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General speedups and cleanups
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Switch from 4 to 8-bit input symbols on all Viterbi decoders
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Support for Altivec on PowerPC
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Support for k=15 r=1/6 Cassini/Mars Pathfinder/Mars Exploration Rover/STEREO code
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Changed license to GNU Lesser General Public License (LGPL)
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feclib version 2.1 June 5 2006
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Added error checking, fixed alignment bug in SSE2 versions of Viterbi decoders causing segfaults
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feclib version 2.1.1 June 6 2006
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Fix test/benchmark time measurement on Linux
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