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113 lines
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>SRFI-27 Random Number Generators (Guile Reference Manual)</title>
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<div class="subsubsection-level-extent" id="SRFI_002d27-Random-Number-Generators">
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<p>
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Previous: <a href="SRFI_002d27-Random-Sources.html" accesskey="p" rel="prev">Random Sources</a>, Up: <a href="SRFI_002d27.html" accesskey="u" rel="up">SRFI-27 - Sources of Random Bits</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<h4 class="subsubsection" id="Obtaining-random-number-generator-procedures"><span>7.5.19.3 Obtaining random number generator procedures<a class="copiable-link" href="#Obtaining-random-number-generator-procedures"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-SRFI_002d27-3"></a>
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<dl class="first-deffn first-defun-alias-first-deffn">
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<dt class="deffn defun-alias-deffn" id="index-random_002dsource_002dmake_002dintegers"><span class="category-def">Function: </span><span><strong class="def-name">random-source-make-integers</strong> <var class="def-var-arguments">source</var><a class="copiable-link" href="#index-random_002dsource_002dmake_002dintegers"> ¶</a></span></dt>
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<dd><p>Obtains a procedure to generate random integers using the random source
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<var class="var">source</var>. The returned procedure takes a single argument <var class="var">n</var>,
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which must be a positive integer, and returns the next uniformly
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distributed random integer from the interval {0, ..., <var class="var">n</var>-1} by
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advancing the state of <var class="var">source</var>.
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</p>
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<p>If an application obtains and uses several generators for the same
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random source <var class="var">source</var>, a call to any of these generators advances
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the state of <var class="var">source</var>. Hence, the generators do not produce the
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same sequence of random integers each but rather share a state. This
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also holds for all other types of generators derived from a fixed random
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sources.
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</p>
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<p>While the SRFI text specifies that “Implementations that support
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concurrency make sure that the state of a generator is properly
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advanced”, this is currently not the case in Guile’s implementation of
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SRFI-27, as it would cause a severe performance penalty. So in
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multi-threaded programs, you either must perform locking on random
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sources shared between threads yourself, or use different random sources
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for multiple threads.
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</p></dd></dl>
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<dl class="first-deffn first-defun-alias-first-deffn">
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<dt class="deffn defun-alias-deffn" id="index-random_002dsource_002dmake_002dreals"><span class="category-def">Function: </span><span><strong class="def-name">random-source-make-reals</strong> <var class="def-var-arguments">source</var><a class="copiable-link" href="#index-random_002dsource_002dmake_002dreals"> ¶</a></span></dt>
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<dt class="deffnx defunx-alias-deffnx def-cmd-deffn" id="index-random_002dsource_002dmake_002dreals-1"><span class="category-def">Function: </span><span><strong class="def-name">random-source-make-reals</strong> <var class="def-var-arguments">source unit</var><a class="copiable-link" href="#index-random_002dsource_002dmake_002dreals-1"> ¶</a></span></dt>
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<dd><p>Obtains a procedure to generate random real numbers <em class="math">0 < x < 1</em>
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using the random source <var class="var">source</var>. The procedure rand is called
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without arguments.
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</p>
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<p>The optional parameter <var class="var">unit</var> determines the type of numbers being
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produced by the returned procedure and the quantization of the output.
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<var class="var">unit</var> must be a number such that <em class="math">0 < <var class="var">unit</var> < 1</em>. The
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numbers created by the returned procedure are of the same numerical type
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as <var class="var">unit</var> and the potential output values are spaced by at most
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<var class="var">unit</var>. One can imagine rand to create numbers as <var class="var">x</var> *
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<var class="var">unit</var> where <var class="var">x</var> is a random integer in {1, ...,
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floor(1/unit)-1}. Note, however, that this need not be the way the
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values are actually created and that the actual resolution of rand can
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be much higher than unit. In case <var class="var">unit</var> is absent it defaults to a
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reasonably small value (related to the width of the mantissa of an
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efficient number format).
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</p></dd></dl>
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<hr>
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<div class="nav-panel">
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<p>
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Previous: <a href="SRFI_002d27-Random-Sources.html">Random Sources</a>, Up: <a href="SRFI_002d27.html">SRFI-27 - Sources of Random Bits</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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