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<?xml version="1.0" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>BN_CTX_start</title> <meta http-equiv="content-type" content="text/html; charset=utf-8" /> <link rev="made" href="mailto:root@hsxx.drive.ne.jp" /> </head> <body style="background-color: white"> <!-- INDEX BEGIN --> <div name="index"> <p><a name="__index__"></a></p> <ul> <li><a href="#name">NAME</a></li> <li><a href="#synopsis">SYNOPSIS</a></li> <li><a href="#description">DESCRIPTION</a></li> <li><a href="#return_values">RETURN VALUES</a></li> <li><a href="#see_also">SEE ALSO</a></li> <li><a href="#copyright">COPYRIGHT</a></li> </ul> <hr name="index" /> </div> <!-- INDEX END --> <p> </p> <hr /> <h1><a name="name">NAME</a></h1> <p>BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables</p> <p> </p> <hr /> <h1><a name="synopsis">SYNOPSIS</a></h1> <pre> #include <openssl/bn.h></pre> <pre> void BN_CTX_start(BN_CTX *ctx);</pre> <pre> BIGNUM *BN_CTX_get(BN_CTX *ctx);</pre> <pre> void BN_CTX_end(BN_CTX *ctx);</pre> <p> </p> <hr /> <h1><a name="description">DESCRIPTION</a></h1> <p>These functions are used to obtain temporary <strong>BIGNUM</strong> variables from a <strong>BN_CTX</strong> (which can been created by using <em>BN_CTX_new(3)</em>) in order to save the overhead of repeatedly creating and freeing <strong>BIGNUM</strong>s in functions that are called from inside a loop.</p> <p>A function must call <code>BN_CTX_start()</code> first. Then, <code>BN_CTX_get()</code> may be called repeatedly to obtain temporary <strong>BIGNUM</strong>s. All <code>BN_CTX_get()</code> calls must be made before calling any other functions that use the <strong>ctx</strong> as an argument.</p> <p>Finally, <code>BN_CTX_end()</code> must be called before returning from the function. If <strong>ctx</strong> is NULL, nothing is done. When <code>BN_CTX_end()</code> is called, the <strong>BIGNUM</strong> pointers obtained from <code>BN_CTX_get()</code> become invalid.</p> <p> </p> <hr /> <h1><a name="return_values">RETURN VALUES</a></h1> <p><code>BN_CTX_start()</code> and <code>BN_CTX_end()</code> return no values.</p> <p><code>BN_CTX_get()</code> returns a pointer to the <strong>BIGNUM</strong>, or <strong>NULL</strong> on error. Once <code>BN_CTX_get()</code> has failed, the subsequent calls will return <strong>NULL</strong> as well, so it is sufficient to check the return value of the last <code>BN_CTX_get()</code> call. In case of an error, an error code is set, which can be obtained by <em>ERR_get_error(3)</em>.</p> <p> </p> <hr /> <h1><a name="see_also">SEE ALSO</a></h1> <p><em>BN_CTX_new(3)</em></p> <p> </p> <hr /> <h1><a name="copyright">COPYRIGHT</a></h1> <p>Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.</p> <p>Licensed under the OpenSSL license (the "License"). 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 <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p> </body> </html>