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&lt;title&gt;BN_CTX_start&lt;/title&gt;
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&lt;ul id=&quot;index&quot;&gt;
  &lt;li&gt;&lt;a href=&quot;#NAME&quot;&gt;NAME&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=&quot;#SYNOPSIS&quot;&gt;SYNOPSIS&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=&quot;#DESCRIPTION&quot;&gt;DESCRIPTION&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=&quot;#RETURN-VALUES&quot;&gt;RETURN VALUES&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=&quot;#SEE-ALSO&quot;&gt;SEE ALSO&lt;/a&gt;&lt;/li&gt;
  &lt;li&gt;&lt;a href=&quot;#COPYRIGHT&quot;&gt;COPYRIGHT&lt;/a&gt;&lt;/li&gt;
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&lt;h1 id=&quot;NAME&quot;&gt;NAME&lt;/h1&gt;

&lt;p&gt;BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables&lt;/p&gt;

&lt;h1 id=&quot;SYNOPSIS&quot;&gt;SYNOPSIS&lt;/h1&gt;

&lt;pre&gt;&lt;code&gt; #include &amp;lt;openssl/bn.h&amp;gt;

 void BN_CTX_start(BN_CTX *ctx);

 BIGNUM *BN_CTX_get(BN_CTX *ctx);

 void BN_CTX_end(BN_CTX *ctx);&lt;/code&gt;&lt;/pre&gt;

&lt;h1 id=&quot;DESCRIPTION&quot;&gt;DESCRIPTION&lt;/h1&gt;

&lt;p&gt;These functions are used to obtain temporary &lt;b&gt;BIGNUM&lt;/b&gt; variables from a &lt;b&gt;BN_CTX&lt;/b&gt; (which can been created by using &lt;a href=&quot;../man3/BN_CTX_new.html&quot;&gt;BN_CTX_new(3)&lt;/a&gt;) in order to save the overhead of repeatedly creating and freeing &lt;b&gt;BIGNUM&lt;/b&gt;s in functions that are called from inside a loop.&lt;/p&gt;

&lt;p&gt;A function must call BN_CTX_start() first. Then, BN_CTX_get() may be called repeatedly to obtain temporary &lt;b&gt;BIGNUM&lt;/b&gt;s. All BN_CTX_get() calls must be made before calling any other functions that use the &lt;b&gt;ctx&lt;/b&gt; as an argument.&lt;/p&gt;

&lt;p&gt;Finally, BN_CTX_end() must be called before returning from the function. If &lt;b&gt;ctx&lt;/b&gt; is NULL, nothing is done. When BN_CTX_end() is called, the &lt;b&gt;BIGNUM&lt;/b&gt; pointers obtained from BN_CTX_get() become invalid.&lt;/p&gt;

&lt;h1 id=&quot;RETURN-VALUES&quot;&gt;RETURN VALUES&lt;/h1&gt;

&lt;p&gt;BN_CTX_start() and BN_CTX_end() return no values.&lt;/p&gt;

&lt;p&gt;BN_CTX_get() returns a pointer to the &lt;b&gt;BIGNUM&lt;/b&gt;, or &lt;b&gt;NULL&lt;/b&gt; on error. Once BN_CTX_get() has failed, the subsequent calls will return &lt;b&gt;NULL&lt;/b&gt; as well, so it is sufficient to check the return value of the last BN_CTX_get() call. In case of an error, an error code is set, which can be obtained by &lt;a href=&quot;../man3/ERR_get_error.html&quot;&gt;ERR_get_error(3)&lt;/a&gt;.&lt;/p&gt;

&lt;h1 id=&quot;SEE-ALSO&quot;&gt;SEE ALSO&lt;/h1&gt;

&lt;p&gt;&lt;a href=&quot;../man3/BN_CTX_new.html&quot;&gt;BN_CTX_new(3)&lt;/a&gt;&lt;/p&gt;

&lt;h1 id=&quot;COPYRIGHT&quot;&gt;COPYRIGHT&lt;/h1&gt;

&lt;p&gt;Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.&lt;/p&gt;

&lt;p&gt;Licensed under the OpenSSL license (the &amp;quot;License&amp;quot;). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at &lt;a href=&quot;https://www.openssl.org/source/license.html&quot;&gt;https://www.openssl.org/source/license.html&lt;/a&gt;.&lt;/p&gt;


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