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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>4.13 Stencil Vectors</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewselflink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="running.html" class="t
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associated mask <a href="numbers.html#%28tech._fixnum%29" class="techoutside" data-pltdoc="x"><span class="techinside">fixnum</span></a> where the number of bits set in the mask
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determines the length of the vector. A stencil vector is useful for
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implementing some data structures [<a href="doc-bibliography.html#%28cite._.Torosyan21%29" data-pltdoc="x">Torosyan21</a>], such as a hash
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array mapped trie (HAMT).</p><p>Conceptually, a stencil vector’s mask indicates which virtual elements
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of a full-sized stencil vector are present, but mask bits have no
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effect on access or mutation via <span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-ref%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-ref</a></span> and
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<span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-set%21%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-set!</a></span>. For example, such a stencil vector has a
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mask <span class="RktVal">25</span>, which could also be written <span class="RktVal">#b11001</span>;
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reading from low bit to high, that mask represents values present at
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the first, fourth, and fifth virtual slots. If that stencil vector’s
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elements are <span class="RktVal">'</span><span class="RktVal">a</span>, <span class="RktVal">'</span><span class="RktVal">b</span>, and <span class="RktVal">'</span><span class="RktVal">c</span>, then
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<span class="RktVal">'</span><span class="RktVal">a</span> is at virtual slot 0 and accessed with index <span class="RktVal">0</span>,
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<span class="RktVal">'</span><span class="RktVal">b</span> is at virtual slot 3 and accessed with index <span class="RktVal">1</span>,
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and <span class="RktVal">'</span><span class="RktVal">c</span> is at virtual slot 4 and accessed with index
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<span class="RktVal">2</span>.</p><p>The relative order of bits in a mask <span class="emph">is</span> relevant for a
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functional-update operation with <span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-update%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-update</a></span>.
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Elements to remove are specified with a removal mask, and elements to
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add are ordered relative to remaining elements through an addition
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mask. For example, starting with the stencil vector whose mask is
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<span class="RktVal">#b11001</span> with elements <span class="RktVal">'</span><span class="RktVal">a</span>, <span class="RktVal">'</span><span class="RktVal">b</span>, and
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<span class="RktVal">'</span><span class="RktVal">c</span>, adding new elements <span class="RktVal">'</span><span class="RktVal">d</span> and <span class="RktVal">'</span><span class="RktVal">e</span> using the
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addition mask <span class="RktVal">#b100100</span> produces a stencil vector whose
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mask is <span class="RktVal">#b111101</span> and whose elements in order are
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<span class="RktVal">'</span><span class="RktVal">a</span>, <span class="RktVal">'</span><span class="RktVal">b</span>, <span class="RktVal">'</span><span class="RktVal">d</span>, <span class="RktVal">'</span><span class="RktVal">c</span>, and <span class="RktVal">'</span><span class="RktVal">e</span>.</p><p>The maximum size of a stencil vector is 58 elements on a 64-bit
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platform and 26 elements on a 32-bit platform. This limited size
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enables a compact internal representation and ensures that update
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operations are relatively simple. Stencil vectors are mutable,
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although they are intended primarily for use without mutation to
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implement a persistent data structure.</p><p>Two stencil vectors are <span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span> if they have the same mask,
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and if the values in corresponding slots of the stencil vectors are
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<span class="RktSym"><a href="Equality.html#%28def._%28%28quote._~23~25kernel%29._equal~3f%29%29" class="RktValLink" data-pltdoc="x">equal?</a></span>.</p><p>A printed vector starts with <span class="RktInBG"><span class="hspace"></span><span class="RktIn">#<stencil ...></span><span class="hspace"></span></span>, and this
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printed form cannot be parsed by <span class="RktSym"><a href="Reading.html#%28def._%28%28quote._~23~25kernel%29._read%29%29" class="RktValLink" data-pltdoc="x">read</a></span>. The
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<span class="RktSym"><a href="fasl.html#%28def._%28%28lib._racket%2Ffasl..rkt%29._s-exp-~3efasl%29%29" class="RktValLink" data-pltdoc="x">s-exp->fasl</a></span> and <span class="RktSym"><a href="serialization.html#%28def._%28%28lib._racket%2Fprivate%2Fserialize..rkt%29._serialize%29%29" class="RktValLink" data-pltdoc="x">serialize</a></span> functions do not support
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stencil vectors, in part because a stencil vector on a 64-bit platform
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might not be representable on a 32-bit platform. The intent is that
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stencil vectors are used as an in-memory representation for a datatype
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implementation.</p><p class="SHistory">Added in version 8.5.0.7 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._stencil-vector~3f))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">stencil-vector?</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">v</span> is a <a href="stencil_vectors.html#%28tech._stencil._vector%29" class="techoutside" data-pltdoc="x"><span class="techinside">stencil vector</span></a>, <span class="RktVal">#f</span> otherwise.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b10010</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">a</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">b</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">#<stencil 18: a b></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b111</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">a</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">b</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">c</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">#<stencil 7: a b c></span></p></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 8.5.0.7 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._stencil-vector-mask-width))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-mask-width%29%29" class="RktValDef RktValLink" data-pltdoc="x">stencil-vector-mask-width</a></span></span><span class="RktPn"></span><span class="Rkt
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the current platform. The result is <span class="RktVal">58</span> on a 64-bit platform
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or <span class="RktVal">26</span> on a 32-bit platform.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._stencil-vector))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector%29%29" class="RktValDef RktValLink" data-pltdoc="x">stencil-vector</a></span></span><span class="hspace"> </span><span class="RktVar">mask</span><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector~3f%29%29" class="RktValLink" data-pltdoc="x">stencil-vector?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">mask</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValLink" data-pltdoc="x">integer-in</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._sub1%29%29" class="RktValLink" data-pltdoc="x">sub1</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._expt%29%29" class="RktValLink" data-pltdoc="x">expt</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-mask-width%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-mask-width</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a stencil vector combining <span class="RktVar">mask</span> with elements
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<span class="RktVar">v</span>. The number of supplied <span class="RktVar">v</span>s must match the number
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of bits set in <span class="RktVar">mask</span>’s two’s complement representation.</div></p><p class="SHistory">Added in version 8.5.0.7 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._stencil-vector-mask))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-mask%29%29" class="RktValDef RktValLink" data-pltdoc="x">stencil-vector-mask</a></span></span><span class="hspace"> </span><span class="RktVar">vec</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValLink" data-pltdoc="x">integer-in</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._sub1%29%29" class="RktValLink" data-pltdoc="x">sub1</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._expt%29%29" class="RktValLink" data-pltdoc="x">expt</a></span><span class="hspace"> </span><span class="RktVal">2</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-mask-width%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-mask-width</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">vec</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector~3f%29%29" class="RktValLink" data-pltdoc="x">stencil-vector?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the mask of <span class="RktVar">vec</span>. Note that the mask of a stencil
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vector is determined at creation time and cannot be changed later.</div></p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-mask</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktMeta">stencil-vector</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b10010</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">a</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">b</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">18</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 8.5.0.7 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._stencil-vector-length))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-length%29%29" class="RktValDef RktValLink" data-pltdoc="x">stencil-vector-length</a></span></span><span class="hspace"> </span><span class="RktVar">vec</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._integer-in%29%29" class="RktValLink" data-pltdoc="x">integer-in</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._sub1%29%29" class="RktValLink" data-pltdoc="x">sub1</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-mask-width%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-mask-width</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">vec</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector~3f%29%29" class="RktValLink" data-pltdoc="x">stencil-vector?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the length of <span class="RktVar">vec</span> (i.e., the number of slots in the
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vector). The result is the same as <span class="RktPn">(</span><span class="RktSym"><a href="fixnums.html#%28def._%28%28lib._racket%2Ffixnum..rkt%29._fxpopcount%29%29" class="RktValLink" data-pltdoc="x">fxpopcount</a></span><span class="stt"> </span><span class="RktPn">(</span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-mask%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-mask</a></span><span class="stt"> </span><span class="RktVar">vec</span><span class="RktPn">)</span><span class="RktPn">)</span>.</div></p><p><div class="SIntrapara">Example:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-length</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktMeta">stencil-vector</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b10010</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">a</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">b</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">2</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 8.5.0.7 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._stencil-vector-ref))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-ref%29%29" class="RktValDef RktValLink" data-pltdoc="x">stencil-vector-ref</a></span></span><span class="hspace"> </span><span class="RktVar">vec</span><span class="hspace"> </span><span class="RktVar">pos</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">vec</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector~3f%29%29" class="RktValLink" data-pltdoc="x">stencil-vector?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the element in slot <span class="RktVar">pos</span> of <span class="RktVar">vec</span>. The first
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slot is position <span class="RktVal">0</span>, and the last slot is one less than
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<span class="RktPn">(</span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-length%29%29" class="RktValLink" data-pltdoc="x">stencil-vector-length</a></span><span class="stt"> </span><span class="RktVar">vec</span><span class="RktPn">)</span>.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-ref</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktMeta">stencil-vector</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b10010</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">a</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">b</span><span class="RktPn">)</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">'b</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-ref</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktMeta">stencil-vector</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b111</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">a</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">b</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">c</span><span class="RktPn">)</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">1</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">'b</span></p></td></tr></table></blockquote></div></p><p class="SHistory">Added in version 8.5.0.7 of package <span class="stt">base</span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._stencil-vector-set!))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector-set%21%29%29" class="RktValDef RktValLink" data-pltdoc="x">stencil-vector-set!</a></span></span><span class="hspace"> </span><span class="RktVar">vec</span><span class="hspace"> </span><span class="RktVar">pos</span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym">avoid?</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">vec</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="stencil_vectors.html#%28def._%28%28quote._~23~25kernel%29._stencil-vector~3f%29%29" class="RktValLink" data-pltdoc="x">stencil-vector?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">pos</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink"
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corresponding to <span class="RktVar">remove-mask</span> removed, and with the given
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<span class="RktVar">v</span>s added at positions relative to existing (unremoved)
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elements determined by <span class="RktVar">add-mask</span>.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">define</span><span class="hspace"> </span><span class="RktMeta">st-vec</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktPn">(</span><span class="RktMeta">stencil-vector</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b101</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">a</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">b</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-update</span><span class="hspace"> </span><span class="RktMeta">st-vec</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b0</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b10</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">c</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">#<stencil 7: a c b></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-update</span><span class="hspace"> </span><span class="RktMeta">st-vec</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b0</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b1000</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">c</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">#<stencil 13: a b c></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktMeta">st-vec</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktCmt">;</span><span class="hspace"> </span><span class="RktCmt">unchanged</span><span class="hspace"> </span><span class="RktCmt">by</span><span class="hspace"> </span><span class="RktCmt">updates</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">#<stencil 5: a b></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-update</span><span class="hspace"> </span><span class="RktMeta">st-vec</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b1</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b1</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span><span class="RktMeta">c</span><span class="RktPn">)</span><span class="RktMeta"></span></td></tr><tr><td><p><span class="RktRes">#<stencil 5: c b></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktMeta">stencil-vector-update</span><span class="hspace"> </span><span class="RktMeta">st-vec</span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b100</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">#b100</span><span class="RktMeta"></span><span class="hspace"> </span><span class="RktMeta"></span><span class="RktVal">'</span
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