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Article contents:== Outdated egg! This is an egg for CHICKEN 4, the unsupported old release. You're almost certainly looking for [[/eggref/5/random-swb|the CHICKEN 5 version of this egg]], if it exists. If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-5.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN. [[tags:egg]] == swb-random A random number generator based on the subtract-with-borrow (SWB) method. [[toc:]] == Usage (require-extension swb-random) == Documentation The swb-random library is a port of the SML/NJ implementation of a random number generator using the subtract-with-borrow (SWB) method described by Marsaglia and Zaman in A New Class of Random Number Generators, Ann. Applied Prob. 1(3), 1991, pp. 462-480. The SWB generator implemented in this library is a 30-bit generator with lags 48 and 8. It has period {{(2^1487 - 2^247)/105}} or about {{10^445}}. The SWB generator acts locally like a lagged Fibonacci generator and thus it is combined with a linear congruential generator {{(48271*a)mod(2^30-1)}}. === Procedures <procedure>make-swb-random-state:: CONG-SEED SHR-SEED -> SWB-STATE</procedure> Creates an initial seed array and generator state. The seed vector is filled one bit at a time by taking the leading bit of the xor of a shift register and a congruential sequence. The congruential generator is {{(c*48271) mod (2^30 - 1)}}. The shift register generator is {{c(I + L18)(I + R13)}}. The same congruential generator continues to be used as a mixing generator with the SWB generator. <procedure>swb-random!:: SWB-STATE -> FIXNUM</procedure> Computes the next random number. The output from the SWB generator is xor-ed with a number from the linear congruential generator. This procedure modifies its input argument. <procedure>swb-random-natural!:: SWB-STATE -> FIXNUM</procedure> Computes the next random number and returns its absolute value. The output from the SWB generator is xor-ed with a number from the linear congruential generator. This procedure modifies its input argument. <procedure>swb-random-real!:: SWB-STATE -> FLONUM</procedure> Computes the two next random numbers and uses them to construct a real number of the range {{[0..1]}}. The output from the SWB generator is xor-ed with a number from the linear congruential generator. This procedure modifies its input argument. <procedure>swb-random-range!:: (FIXNUM * FIXNUM) -> (SWB-STATE -> FIXNUM)</procedure> Given a range {{[i..j], 0 <= i < j}}, returns a procedure that takes in a random number generator state and computes a random number in the given range. The output from the SWB generator is xor-ed with a number from the linear congruential generator. The returned procedure modifies its input argument. <procedure>swb-random:: SWB-STATE -> SWB-STATE * FIXNUM</procedure> Computes the next random number. The output from the SWB generator is xor-ed with a number from the linear congruential generator. The new generator state is returned along with the random number. <procedure>swb-random-natural:: SWB-STATE -> SWB-STATE * FIXNUM</procedure> Computes the next random number and returns its absolute values. The output from the SWB generator is xor-ed with a number from the linear congruential generator. The new generator state is returned along with the random number. <procedure>swb-random-real:: SWB-STATE -> SWB-STATE * FLONUM</procedure> Computes the two next random numbers and uses them to construct a real number of the range {{[0..1]}}. The output from the SWB generator is xor-ed with a number from the linear congruential generator. The new generator state is returned along with the random number. <procedure>swb-random-range:: (FIXNUM * FIXNUM) -> (SWB-STATE -> SWB-STATE * FIXNUM)</procedure> Given a range {{[i..j], 0 <= i < j}}, returns a procedure that takes in a random number generator state and computes a random number in the given range. The output from the SWB generator is xor-ed with a number from the linear congruential generator. The new generator state is returned along with the random number. == About this egg === Author [[/users/ivan-raikov|Ivan Raikov]] === Version history ; 1.12 : Documentation converted to wiki format ; 1.11 : Added import of foreign library [thanks to felix] ; 1.9 : Added matchable as a dependency ; 1.8 : Bug fix in interface to cminus function ; 1.7 : Ported to Chicken 4 ; 1.5 : Bug fix in the setup file ; 1.4 : Removed easyffi dependency ; 1.3 : Build script updated for better cross-platform compatibility ; 1.2 : Fixed the .meta file to include the documentation ; 1.1 : License upgrade to GPL v3 ; 1.0 : Initial release === License Copyright 2007-2010 Ivan Raikov. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. A full copy of the GPL license can be found at <http://www.gnu.org/licenses/>. Description of your changes:

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