BN_CTX_start.pod 1.6 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
=pod

=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
R
Rich Salz 已提交
20
a B<BN_CTX> (which can been created by using L<BN_CTX_new(3)>)
21
in order to save the overhead of repeatedly creating and
22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
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
40
BN_CTX_get() call. In case of an error, an error code is set, which
R
Rich Salz 已提交
41
can be obtained by L<ERR_get_error(3)>.
42

43 44 45

=head1 SEE ALSO

R
Rich Salz 已提交
46
L<BN_CTX_new(3)>
47 48

=cut
R
Rich Salz 已提交
49 50 51 52 53 54 55 56 57 58 59

=head1 COPYRIGHT

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

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
L<https://www.openssl.org/source/license.html>.

=cut