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140 .IX Title "BN_CTX_START 1"
141 .TH BN_CTX_START 1 "perl v5.6.1" "2000-11-13" "User Contributed Perl Documentation"
144 BN_CTX_start, BN_CTX_get, BN_CTX_end \- use temporary \s-1BIGNUM\s0 variables
146 .IX Header "SYNOPSIS"
148 \& #include <openssl/bn.h>
151 \& void BN_CTX_start(BN_CTX *ctx);
154 \& BIGNUM *BN_CTX_get(BN_CTX *ctx);
157 \& void BN_CTX_end(BN_CTX *ctx);
160 .IX Header "DESCRIPTION"
161 These functions are used to obtain temporary \fB\s-1BIGNUM\s0\fR variables from
162 a \fB\s-1BN_CTX\s0\fR (which can been created by using BN_CTX_new(3))
163 in order to save the overhead of repeatedly creating and
164 freeing \fB\s-1BIGNUM\s0\fRs in functions that are called from inside a loop.
166 A function must call \fIBN_CTX_start()\fR first. Then, \fIBN_CTX_get()\fR may be
167 called repeatedly to obtain temporary \fB\s-1BIGNUM\s0\fRs. All \fIBN_CTX_get()\fR
168 calls must be made before calling any other functions that use the
169 \&\fBctx\fR as an argument.
171 Finally, \fIBN_CTX_end()\fR must be called before returning from the function.
172 When \fIBN_CTX_end()\fR is called, the \fB\s-1BIGNUM\s0\fR pointers obtained from
173 \&\fIBN_CTX_get()\fR become invalid.
175 .IX Header "RETURN VALUES"
176 \&\fIBN_CTX_start()\fR and \fIBN_CTX_end()\fR return no values.
178 \&\fIBN_CTX_get()\fR returns a pointer to the \fB\s-1BIGNUM\s0\fR, or \fB\s-1NULL\s0\fR on error.
179 Once \fIBN_CTX_get()\fR has failed, the subsequent calls will return \fB\s-1NULL\s0\fR
180 as well, so it is sufficient to check the return value of the last
181 \&\fIBN_CTX_get()\fR call. In case of an error, an error code is set, which
182 can be obtained by ERR_get_error(3).
184 .IX Header "SEE ALSO"
188 \&\fIBN_CTX_start()\fR, \fIBN_CTX_get()\fR and \fIBN_CTX_end()\fR were added in OpenSSL 0.9.5.