165 lines
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165 lines
6 KiB
HTML
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>SRFI-4 Overview (Guile Reference Manual)</title>
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<link href="SRFI_002d4.html" rel="up" title="SRFI-4">
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<div class="subsubsection-level-extent" id="SRFI_002d4-Overview">
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<p>
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Next: <a href="SRFI_002d4-API.html" accesskey="n" rel="next">SRFI-4 - API</a>, Up: <a href="SRFI_002d4.html" accesskey="u" rel="up">SRFI-4 - Homogeneous numeric vector datatypes</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="SRFI_002d4-_002d-Overview"><span>7.5.5.1 SRFI-4 - Overview<a class="copiable-link" href="#SRFI_002d4-_002d-Overview"> ¶</a></span></h4>
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<p>Uniform numeric vectors can be useful since they consume less memory
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than the non-uniform, general vectors. Also, since the types they can
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store correspond directly to C types, it is easier to work with them
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efficiently on a low level. Consider image processing as an example,
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where you want to apply a filter to some image. While you could store
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the pixels of an image in a general vector and write a general
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convolution function, things are much more efficient with uniform
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vectors: the convolution function knows that all pixels are unsigned
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8-bit values (say), and can use a very tight inner loop.
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</p>
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<p>This is implemented in Scheme by having the compiler notice calls to the SRFI-4
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accessors, and inline them to appropriate compiled code. From C you have access
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to the raw array; functions for efficiently working with uniform numeric vectors
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from C are listed at the end of this section.
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</p>
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<p>Uniform numeric vectors are the special case of one dimensional uniform
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numeric arrays.
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</p>
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<p>There are 12 standard kinds of uniform numeric vectors, and they all have their
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own complement of constructors, accessors, and so on. Procedures that operate on
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a specific kind of uniform numeric vector have a “tag” in their name,
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indicating the element type.
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</p>
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<dl class="table">
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<dt><code class="code">u8</code></dt>
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<dd><p>unsigned 8-bit integers
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</p>
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</dd>
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<dt><code class="code">s8</code></dt>
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<dd><p>signed 8-bit integers
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</p>
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</dd>
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<dt><code class="code">u16</code></dt>
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<dd><p>unsigned 16-bit integers
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</p>
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</dd>
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<dt><code class="code">s16</code></dt>
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<dd><p>signed 16-bit integers
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</p>
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</dd>
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<dt><code class="code">u32</code></dt>
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<dd><p>unsigned 32-bit integers
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</p>
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</dd>
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<dt><code class="code">s32</code></dt>
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<dd><p>signed 32-bit integers
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</p>
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</dd>
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<dt><code class="code">u64</code></dt>
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<dd><p>unsigned 64-bit integers
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</p>
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</dd>
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<dt><code class="code">s64</code></dt>
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<dd><p>signed 64-bit integers
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</p>
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</dd>
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<dt><code class="code">f32</code></dt>
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<dd><p>the C type <code class="code">float</code>
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</p>
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</dd>
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<dt><code class="code">f64</code></dt>
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<dd><p>the C type <code class="code">double</code>
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</p>
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</dd>
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</dl>
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<p>In addition, Guile supports uniform arrays of complex numbers, with the
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nonstandard tags:
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</p>
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<dl class="table">
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<dt><code class="code">c32</code></dt>
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<dd><p>complex numbers in rectangular form with the real and imaginary part
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being a <code class="code">float</code>
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</p>
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</dd>
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<dt><code class="code">c64</code></dt>
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<dd><p>complex numbers in rectangular form with the real and imaginary part
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being a <code class="code">double</code>
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</p>
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</dd>
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</dl>
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<p>The external representation (ie. read syntax) for these vectors is
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similar to normal Scheme vectors, but with an additional tag from the
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tables above indicating the vector’s type. For example,
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">#u16(1 2 3)
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#f64(3.1415 2.71)
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</pre></div>
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<p>Note that the read syntax for floating-point here conflicts with
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<code class="code">#f</code> for false. In Standard Scheme one can write <code class="code">(1 #f3)</code>
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for a three element list <code class="code">(1 #f 3)</code>, but for Guile <code class="code">(1 #f3)</code>
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is invalid. <code class="code">(1 #f 3)</code> is almost certainly what one should write
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anyway to make the intention clear, so this is rarely a problem.
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</p>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="SRFI_002d4-API.html">SRFI-4 - API</a>, Up: <a href="SRFI_002d4.html">SRFI-4 - Homogeneous numeric vector datatypes</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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