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=head1 NAME

BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables

=head1 SYNOPSIS

 #include <openssl/bn.h>

 void BN_CTX_start(BN_CTX *ctx);

 BIGNUM *BN_CTX_get(BN_CTX *ctx);

 void BN_CTX_end(BN_CTX *ctx);

=head1 DESCRIPTION

These functions are used to obtain temporary B<BIGNUM> variables from
a B<BN_CTX> (which can been created by using L<BN_CTX_new(3)>)
in order to save the overhead of repeatedly creating and
freeing B<BIGNUM>s in functions that are called from inside a loop.

A function must call BN_CTX_start() first. Then, BN_CTX_get() may be
called repeatedly to obtain temporary B<BIGNUM>s. All BN_CTX_get()
calls must be made before calling any other functions that use the
B<ctx> as an argument.

Finally, BN_CTX_end() must be called before returning from the function.
When BN_CTX_end() is called, the B<BIGNUM> pointers obtained from
BN_CTX_get() become invalid.

=head1 RETURN VALUES

BN_CTX_start() and BN_CTX_end() return no values.

BN_CTX_get() returns a pointer to the B<BIGNUM>, or B<NULL> on error.
Once BN_CTX_get() has failed, the subsequent calls will return B<NULL>
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 L<ERR_get_error(3)>.


=head1 SEE ALSO

L<BN_CTX_new(3)>

=head1 COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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
L<https://www.openssl.org/source/license.html>.

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