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131 .IX Title "BN_CTX_start 3"
132 .TH BN_CTX_start 3 "2009-07-23" "0.9.8k" "OpenSSL"
134 BN_CTX_start, BN_CTX_get, BN_CTX_end \- use temporary BIGNUM variables
136 .IX Header "SYNOPSIS"
138 \& #include <openssl/bn.h>
142 \& void BN_CTX_start(BN_CTX *ctx);
146 \& BIGNUM *BN_CTX_get(BN_CTX *ctx);
150 \& void BN_CTX_end(BN_CTX *ctx);
153 .IX Header "DESCRIPTION"
154 These functions are used to obtain temporary \fB\s-1BIGNUM\s0\fR variables from
155 a \fB\s-1BN_CTX\s0\fR (which can been created by using \fIBN_CTX_new\fR\|(3))
156 in order to save the overhead of repeatedly creating and
157 freeing \fB\s-1BIGNUM\s0\fRs in functions that are called from inside a loop.
159 A function must call \fIBN_CTX_start()\fR first. Then, \fIBN_CTX_get()\fR may be
160 called repeatedly to obtain temporary \fB\s-1BIGNUM\s0\fRs. All \fIBN_CTX_get()\fR
161 calls must be made before calling any other functions that use the
162 \&\fBctx\fR as an argument.
164 Finally, \fIBN_CTX_end()\fR must be called before returning from the function.
165 When \fIBN_CTX_end()\fR is called, the \fB\s-1BIGNUM\s0\fR pointers obtained from
166 \&\fIBN_CTX_get()\fR become invalid.
168 .IX Header "RETURN VALUES"
169 \&\fIBN_CTX_start()\fR and \fIBN_CTX_end()\fR return no values.
171 \&\fIBN_CTX_get()\fR returns a pointer to the \fB\s-1BIGNUM\s0\fR, or \fB\s-1NULL\s0\fR on error.
172 Once \fIBN_CTX_get()\fR has failed, the subsequent calls will return \fB\s-1NULL\s0\fR
173 as well, so it is sufficient to check the return value of the last
174 \&\fIBN_CTX_get()\fR call. In case of an error, an error code is set, which
175 can be obtained by \fIERR_get_error\fR\|(3).
177 .IX Header "SEE ALSO"
178 \&\fIBN_CTX_new\fR\|(3)
181 \&\fIBN_CTX_start()\fR, \fIBN_CTX_get()\fR and \fIBN_CTX_end()\fR were added in OpenSSL 0.9.5.