1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>__atomic_add_unless</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Linux Device Drivers"><link rel="up" href="ch01s02.html" title="Atomic and pointer manipulation"><link rel="prev" href="API-atomic-sub-return.html" title="atomic_sub_return"><link rel="next" href="API-atomic-inc-short.html" title="atomic_inc_short"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span class="phrase">__atomic_add_unless</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-atomic-sub-return.html">Prev</a>&#160;</td><th width="60%" align="center">Atomic and pointer manipulation</th><td width="20%" align="right">&#160;<a accesskey="n" href="API-atomic-inc-short.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API---atomic-add-unless"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>__atomic_add_unless &#8212; 
2     add unless the number is already a given value
3 </p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">__atomic_add_unless </b>(</code></td><td>atomic_t * <var class="pdparam">v</var>, </td></tr><tr><td>&#160;</td><td>int <var class="pdparam">a</var>, </td></tr><tr><td>&#160;</td><td>int <var class="pdparam">u</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer">&#160;</div></div></div><div class="refsect1"><a name="idp1106660716"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>v</code></em></span></dt><dd><p>
4     pointer of type atomic_t
5    </p></dd><dt><span class="term"><em class="parameter"><code>a</code></em></span></dt><dd><p>
6     the amount to add to v...
7    </p></dd><dt><span class="term"><em class="parameter"><code>u</code></em></span></dt><dd><p>
8     ...unless v is equal to u.
9    </p></dd></dl></div></div><div class="refsect1"><a name="idp1106664284"></a><h2>Description</h2><p>
10   Atomically adds <em class="parameter"><code>a</code></em> to <em class="parameter"><code>v</code></em>, so long as <em class="parameter"><code>v</code></em> was not already <em class="parameter"><code>u</code></em>.
11   Returns the old value of <em class="parameter"><code>v</code></em>.
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