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@@ -0,0 +1,120 @@ +COPYRIGHT + +This package is copyright 2006 by Phil Karn, KA9Q. It may be used +under the terms of the GNU Lesser General Public License (LGPL). See +the file "lesser.txt" in this package for license details. + +INTRODUCTION + +This package provides a set of functions that implement several +popular forward error correction (FEC) algorithms and several low-level routines +useful in modems implemented with digital signal processing (DSP). + +The following routines are provided: + +1. Viterbi decoders for the following convolutional codes: + +r=1/2 k=7 ("Voyager" code, now a widely used industry standard) +r=1/2 k=9 (Used on the IS-95 CDMA forward link) +r=1/6 k=15 ("Cassini" code, used by several NASA/JPL deep space missions) + +2. Reed-Solomon encoders and decoders for any user-specified code. + +3. Optimized encoder and decoder for the CCSDS-standard (255,223) +Reed-Solomon code, with and without the CCSDS-standard "dual basis" +symbol representation. + +4. Compute dot product between a 16-bit buffer and a set of 16-bit +coefficients. This is the basic DSP primitive for digital filtering +and correlation. + +4. Compute sum of squares of a buffer of 16-bit signed integers. This is +useful in DSP for finding the total energy in a signal. + +5. Find peak value in a buffer of 16-bit signed integers, useful for +scaling a signal to prevent overflow. + +SIMD SUPPORT + +This package automatically makes use of various SIMD (Single +Instruction stream, Multiple Data stream) instruction sets, when +available: MMX, SSE and SSE2 on the IA-32 (Intel) architecture, and +Altivec on the PowerPC G4 and G5 used by Power Macintoshes. + +"Altivec" is a Motorola trademark; Apple calls it "Velocity Engine", +and IBM calls it "VMX". Altivec is roughly comparable to SSE2 on the +IA-32. + +Many of the SIMD versions run more than an order of +magnitude faster than their portable C versions. The available SIMD +instruction sets, if any, are determined at run time and the proper +version of each routine is automatically selected. If no SIMD +instructions are available, the portable C version is invoked by +default. On targets other than IA-32 and PPC, only the portable C +version is built. + +The SIMD-assisted versions generally produce the same results as the C +versions, with a few minor exceptions. The Viterbi decoders in C have +a very slightly greater Eb/No performance due to their use of 32-bit +path metrics. On the other hand, the SIMD versions use the +"saturating" arithmetic available in these instructions to avoid the +integer wraparounds that can occur in C when argument ranges are not +properly constrained. This applies primarily to the "dotprod" (dot +product) function. + +The MMX (MultiMedia eXtensions) instruction set was introduced on +later Pentium CPUs; it is also implemented on the Pentium II and most +AMD CPUs starting with the K6. SSE (SIMD Streaming Extensions) was +introduced in the Pentium III; AMD calls it "3D Now! Professional". +Intel introduced SSE2 on the Pentium 4, and it has been picked up by +later AMD CPUs. SSE support implies MMX support, while SSE2 support +implies both SSE and MMX support. + +The latest IA-32 SIMD instruction set, SSE3 (also known as "Prescott +New Instructions") was introduced in early 2004 with the latest +("Prescott") revision of the Pentium 4. Relatively little was +introduced with SSE3, and this library currently makes no use of it. + +See the various manual pages for details on how to use the library +routines. + +Copyright 2006, Phil Karn, KA9Q +karn@ka9q.net +http://www.ka9q.net/ + +This software may be used under the terms of the GNU Lesser General +Public License (LGPL); see the file lesser.txt for details. + +Revision history: +Version 1.0 released 29 May 2001 + +Version 2.0 released 3 Dec 2001: +Restructured to add support for shared libraries. + +Version 2.0.1 released 8 Dec 2001: +Includes autoconf/configure script + +Version 2.0.2 released 4 Feb 2002: +Add SIMD version override options +Test for lack of SSE2 mnemonic support in 'as' +Build only selected version + +Version 2.0.3 released 6 Feb 2002: +Fix to parityb function in parity.h + +feclib version 1.0 released November 2003 +Merged SIMD-Viterbi, RS and DSP libraries +Changed SIMD Viterbi decoder to detect SSE2/SSE/MMX at runtime rather than build time + +feclib version 2.0 (unreleased) Mar 2004 +General speedups and cleanups +Switch from 4 to 8-bit input symbols on all Viterbi decoders +Support for Altivec on PowerPC +Support for k=15 r=1/6 Cassini/Mars Pathfinder/Mars Exploration Rover/STEREO code +Changed license to GNU Lesser General Public License (LGPL) + +feclib version 2.1 June 5 2006 +Added error checking, fixed alignment bug in SSE2 versions of Viterbi decoders causing segfaults + +feclib version 2.1.1 June 6 2006 +Fix test/benchmark time measurement on Linux |