mirror of
https://github.com/ganelson/inform.git
synced 2024-07-05 00:24:22 +03:00
191 lines
21 KiB
HTML
191 lines
21 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<head>
|
|
<title>Local Parking</title>
|
|
<link href="../docs-assets/Breadcrumbs.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<meta name="viewport" content="width=device-width initial-scale=1">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<meta http-equiv="Content-Language" content="en-gb">
|
|
|
|
<link href="../docs-assets/Contents.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Progress.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Navigation.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Fonts.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Base.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<script>
|
|
function togglePopup(material_id) {
|
|
var popup = document.getElementById(material_id);
|
|
popup.classList.toggle("show");
|
|
}
|
|
</script>
|
|
|
|
<link href="../docs-assets/Popups.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
<link href="../docs-assets/Colours.css" rel="stylesheet" rev="stylesheet" type="text/css">
|
|
|
|
</head>
|
|
<body class="commentary-font">
|
|
<nav role="navigation">
|
|
<h1><a href="../index.html">
|
|
<img src="../docs-assets/Inform.png" height=72">
|
|
</a></h1>
|
|
<ul><li><a href="../index.html">home</a></li>
|
|
</ul><h2>Compiler</h2><ul>
|
|
<li><a href="../structure.html">structure</a></li>
|
|
<li><a href="../inbuildn.html">inbuild</a></li>
|
|
<li><a href="../inform7n.html">inform7</a></li>
|
|
<li><a href="../intern.html">inter</a></li>
|
|
<li><a href="../services.html">services</a></li>
|
|
<li><a href="../secrets.html">secrets</a></li>
|
|
</ul><h2>Other Tools</h2><ul>
|
|
<li><a href="../inblorbn.html">inblorb</a></li>
|
|
<li><a href="../indocn.html">indoc</a></li>
|
|
<li><a href="../inform6.html">inform6</a></li>
|
|
<li><a href="../inpolicyn.html">inpolicy</a></li>
|
|
<li><a href="../inrtpsn.html">inrtps</a></li>
|
|
</ul><h2>Resources</h2><ul>
|
|
<li><a href="../extensions.html">extensions</a></li>
|
|
<li><a href="../kits.html">kits</a></li>
|
|
</ul><h2>Repository</h2><ul>
|
|
<li><a href="https://github.com/ganelson/inform"><img src="../docs-assets/github.png" height=18> github</a></li>
|
|
</ul><h2>Related Projects</h2><ul>
|
|
<li><a href="../../../inweb/index.html">inweb</a></li>
|
|
<li><a href="../../../intest/index.html">intest</a></li>
|
|
|
|
</ul>
|
|
</nav>
|
|
<main role="main">
|
|
<!--Weave of 'Local Parking' generated by Inweb-->
|
|
<div class="breadcrumbs">
|
|
<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../inform7n.html">Inform7</a></li><li><a href="index.html">imperative</a></li><li><a href="index.html#3">Chapter 3: Functions</a></li><li><b>Local Parking</b></li></ul></div>
|
|
<p class="purpose">Like Free Parking in Monopoly, except that it is not free and has an overhead cost.</p>
|
|
|
|
<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. </b>This is one of several devices we employ to get around the lack of a call stack
|
|
in memory. Suppose we want the local variables in function A to be visible to
|
|
function B, which is called from A, and suppose they cannot be passed as call
|
|
parameters to B. B cannot access them using pointers to the stack frame for A,
|
|
because the call stack does not exist in memory. What to do?
|
|
</p>
|
|
|
|
<p class="commentary">What we do is to stash them into a "local parking" array, make the call to B,
|
|
and then in the code for B retrieve them again. A paraphrase might look
|
|
like this:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax">void A(void) {</span>
|
|
<span class="plain-syntax"> int alpha = 2, beta = 3, gamma = 5;</span>
|
|
<span class="plain-syntax"> lp[0] = alpha;</span>
|
|
<span class="plain-syntax"> lp[1] = beta;</span>
|
|
<span class="plain-syntax"> lp[2] = gamma;</span>
|
|
<span class="plain-syntax"> B();</span>
|
|
<span class="plain-syntax">}</span>
|
|
|
|
<span class="plain-syntax">void B(void) {</span>
|
|
<span class="plain-syntax"> int alpha = lp[0];</span>
|
|
<span class="plain-syntax"> int beta = lp[1];</span>
|
|
<span class="plain-syntax"> int gamma = lp[2];</span>
|
|
<span class="plain-syntax"> ...</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<p class="commentary">Note that B can now read, but not write, the locals from A. The scratch array
|
|
<span class="extract"><span class="extract-syntax">lp</span></span> used here for storage is meaningless except for immediately before and
|
|
after the call to B, so we don't need to worry about multiple uses of local
|
|
parking getting in each other's way.
|
|
</p>
|
|
|
|
<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>§2. </b>This compiles the necessary code before the call to B:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="function-syntax">LocalParking::park</span><span class="plain-syntax">(</span><span class="reserved-syntax">stack_frame</span><span class="plain-syntax"> *</span><span class="identifier-syntax">frame</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">NC</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">local_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">lvar</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">LOOP_OVER_LOCALS_IN_FRAME</span><span class="plain-syntax">(</span><span class="identifier-syntax">lvar</span><span class="plain-syntax">, </span><span class="identifier-syntax">frame</span><span class="plain-syntax">) </span><span class="identifier-syntax">NC</span><span class="plain-syntax">++;</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_name</span><span class="plain-syntax"> *</span><span class="identifier-syntax">park</span><span class="plain-syntax"> = </span><a href="3-lp.html#SP4" class="function-link"><span class="function-syntax">LocalParking::array</span></a><span class="plain-syntax">((</span><span class="identifier-syntax">NC</span><span class="plain-syntax"><2)?2:</span><span class="identifier-syntax">NC</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_ti</span><span class="plain-syntax"> </span><span class="identifier-syntax">j</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">LOOP_OVER_LOCALS_IN_FRAME</span><span class="plain-syntax">(</span><span class="identifier-syntax">lvar</span><span class="plain-syntax">, </span><span class="identifier-syntax">frame</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::inv</span><span class="plain-syntax">(</span><span class="identifier-syntax">SEQUENTIAL_BIP</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::down</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::inv</span><span class="plain-syntax">(</span><span class="identifier-syntax">STORE_BIP</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::down</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::reference</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::down</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::inv</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOOKUP_BIP</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::down</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::val_iname</span><span class="plain-syntax">(</span><span class="identifier-syntax">K_value</span><span class="plain-syntax">, </span><span class="identifier-syntax">park</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::val_number</span><span class="plain-syntax">(</span><span class="identifier-syntax">j</span><span class="plain-syntax">++);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::up</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::up</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_symbol</span><span class="plain-syntax"> *</span><span class="identifier-syntax">lvar_s</span><span class="plain-syntax"> = </span><a href="3-lv.html#SP1" class="function-link"><span class="function-syntax">LocalVariables::declare</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">lvar</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::val_symbol</span><span class="plain-syntax">(</span><span class="identifier-syntax">K_value</span><span class="plain-syntax">, </span><span class="identifier-syntax">lvar_s</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::up</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> }</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">NC</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>§3. </b>And this compiles the retrieval code just after B begins:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">LocalParking::retrieve</span><span class="plain-syntax">(</span><span class="reserved-syntax">stack_frame</span><span class="plain-syntax"> *</span><span class="identifier-syntax">frame</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_name</span><span class="plain-syntax"> *</span><span class="identifier-syntax">park</span><span class="plain-syntax"> = </span><a href="3-lp.html#SP4" class="function-link"><span class="function-syntax">LocalParking::array</span></a><span class="plain-syntax">(0);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_ti</span><span class="plain-syntax"> </span><span class="identifier-syntax">j</span><span class="plain-syntax">=0;</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">local_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">lvar</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">LOOP_OVER_LOCALS_IN_FRAME</span><span class="plain-syntax">(</span><span class="identifier-syntax">lvar</span><span class="plain-syntax">, </span><span class="identifier-syntax">frame</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::inv</span><span class="plain-syntax">(</span><span class="identifier-syntax">STORE_BIP</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::down</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::ref_symbol</span><span class="plain-syntax">(</span><span class="identifier-syntax">K_value</span><span class="plain-syntax">, </span><a href="3-lv.html#SP1" class="function-link"><span class="function-syntax">LocalVariables::declare</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">lvar</span><span class="plain-syntax">));</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::inv</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOOKUP_BIP</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::down</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::val_iname</span><span class="plain-syntax">(</span><span class="identifier-syntax">K_value</span><span class="plain-syntax">, </span><span class="identifier-syntax">park</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::val_number</span><span class="plain-syntax">(</span><span class="identifier-syntax">j</span><span class="plain-syntax">++);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::up</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitCode::up</span><span class="plain-syntax">();</span>
|
|
<span class="plain-syntax"> }</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>§4. </b>We just need <span class="extract"><span class="extract-syntax">park</span></span> to be large enough for the maximum number of cars ever
|
|
needing to be parked:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">size_of_local_parking_area</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
|
|
<span class="identifier-syntax">inter_name</span><span class="plain-syntax"> *</span><span class="function-syntax">LocalParking::array</span><button class="popup" onclick="togglePopup('usagePopup1')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup1">Usage of <span class="code-font"><span class="function-syntax">LocalParking::array</span></span>:<br/><a href="3-lp.html#SP2">§2</a>, <a href="3-lp.html#SP3">§3</a>, <a href="3-lp.html#SP5">§5</a>, <a href="3-lp.html#SP6">§6</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">N</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">N</span><span class="plain-syntax"> > </span><span class="identifier-syntax">size_of_local_parking_area</span><span class="plain-syntax">) </span><span class="identifier-syntax">size_of_local_parking_area</span><span class="plain-syntax"> = </span><span class="identifier-syntax">N</span><span class="plain-syntax">;</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">Hierarchy::find</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOCALPARKING_HL</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>§5. </b>We also sometimes need the same park to hold returned callings from deferred
|
|
propositions; and that needs to be large enough to hold values of up to 26
|
|
variables, plus a single other value.
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="identifier-syntax">inter_name</span><span class="plain-syntax"> *</span><span class="function-syntax">LocalParking::callings</span><button class="popup" onclick="togglePopup('usagePopup2')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup2">Usage of <span class="code-font"><span class="function-syntax">LocalParking::callings</span></span>:<br/>Deciding to Defer - <a href="4-dtd.html#SP7">§7</a>, <a href="4-dtd.html#SP8">§8</a><br/>Compile Deferred Propositions - <a href="4-cdp.html#SP3_6_1_4_5">§3.6.1.4.5</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">void</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="3-lp.html#SP4" class="function-link"><span class="function-syntax">LocalParking::array</span></a><span class="plain-syntax">(27);</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<p class="commentary firstcommentary"><a id="SP6" class="paragraph-anchor"></a><b>§6. </b>So this makes a suitably-sized car park, if one is needed at all:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">LocalParking::compile_array</span><span class="plain-syntax">(</span><span class="reserved-syntax">void</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">size_of_local_parking_area</span><span class="plain-syntax"> > </span><span class="constant-syntax">0</span><span class="plain-syntax">) {</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">inter_name</span><span class="plain-syntax"> *</span><span class="identifier-syntax">iname</span><span class="plain-syntax"> = </span><a href="3-lp.html#SP4" class="function-link"><span class="function-syntax">LocalParking::array</span></a><span class="plain-syntax">(0);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">packaging_state</span><span class="plain-syntax"> </span><span class="identifier-syntax">save</span><span class="plain-syntax"> = </span><span class="identifier-syntax">EmitArrays::begin_word</span><span class="plain-syntax">(</span><span class="identifier-syntax">iname</span><span class="plain-syntax">, </span><span class="identifier-syntax">K_value</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">for</span><span class="plain-syntax"> (</span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">i</span><span class="plain-syntax">=0; </span><span class="identifier-syntax">i</span><span class="plain-syntax"><</span><span class="identifier-syntax">size_of_local_parking_area</span><span class="plain-syntax">; </span><span class="identifier-syntax">i</span><span class="plain-syntax">++)</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitArrays::numeric_entry</span><span class="plain-syntax">(0);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">EmitArrays::end</span><span class="plain-syntax">(</span><span class="identifier-syntax">save</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">Hierarchy::make_available</span><span class="plain-syntax">(</span><span class="identifier-syntax">iname</span><span class="plain-syntax">);</span>
|
|
<span class="plain-syntax"> }</span>
|
|
<span class="plain-syntax">}</span>
|
|
</pre>
|
|
<nav role="progress"><div class="progresscontainer">
|
|
<ul class="progressbar"><li class="progressprev"><a href="3-tv.html">❮</a></li><li class="progresschapter"><a href="P-wtmd.html">P</a></li><li class="progresschapter"><a href="1-im.html">1</a></li><li class="progresschapter"><a href="2-cv.html">2</a></li><li class="progresscurrentchapter">3</li><li class="progresssection"><a href="3-sf.html">sf</a></li><li class="progresssection"><a href="3-lvs.html">lvs</a></li><li class="progresssection"><a href="3-lv.html">lv</a></li><li class="progresssection"><a href="3-tv.html">tv</a></li><li class="progresscurrent">lp</li><li class="progresssection"><a href="3-cb.html">cb</a></li><li class="progresssection"><a href="3-fnc.html">fnc</a></li><li class="progresssection"><a href="3-jl.html">jl</a></li><li class="progresssection"><a href="3-pr.html">pr</a></li><li class="progresssection"><a href="3-cls.html">cls</a></li><li class="progresssection"><a href="3-cid.html">cid</a></li><li class="progresschapter"><a href="4-cs.html">4</a></li><li class="progresschapter"><a href="5-cbal.html">5</a></li><li class="progressnext"><a href="3-cb.html">❯</a></li></ul></div>
|
|
</nav><!--End of weave-->
|
|
|
|
</main>
|
|
</body>
|
|
</html>
|
|
|