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134 .IX Title "BN_CTX_start 3"
135 .TH BN_CTX_start 3 "2009-11-06" "0.9.8l" "OpenSSL"
136 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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141 BN_CTX_start, BN_CTX_get, BN_CTX_end \- use temporary BIGNUM variables
143 .IX Header "SYNOPSIS"
145 \& #include <openssl/bn.h>
147 \& void BN_CTX_start(BN_CTX *ctx);
149 \& BIGNUM *BN_CTX_get(BN_CTX *ctx);
151 \& void BN_CTX_end(BN_CTX *ctx);
154 .IX Header "DESCRIPTION"
155 These functions are used to obtain temporary \fB\s-1BIGNUM\s0\fR variables from
156 a \fB\s-1BN_CTX\s0\fR (which can been created by using \fIBN_CTX_new\fR\|(3))
157 in order to save the overhead of repeatedly creating and
158 freeing \fB\s-1BIGNUM\s0\fRs in functions that are called from inside a loop.
160 A function must call \fIBN_CTX_start()\fR first. Then, \fIBN_CTX_get()\fR may be
161 called repeatedly to obtain temporary \fB\s-1BIGNUM\s0\fRs. All \fIBN_CTX_get()\fR
162 calls must be made before calling any other functions that use the
163 \&\fBctx\fR as an argument.
165 Finally, \fIBN_CTX_end()\fR must be called before returning from the function.
166 When \fIBN_CTX_end()\fR is called, the \fB\s-1BIGNUM\s0\fR pointers obtained from
167 \&\fIBN_CTX_get()\fR become invalid.
169 .IX Header "RETURN VALUES"
170 \&\fIBN_CTX_start()\fR and \fIBN_CTX_end()\fR return no values.
172 \&\fIBN_CTX_get()\fR returns a pointer to the \fB\s-1BIGNUM\s0\fR, or \fB\s-1NULL\s0\fR on error.
173 Once \fIBN_CTX_get()\fR has failed, the subsequent calls will return \fB\s-1NULL\s0\fR
174 as well, so it is sufficient to check the return value of the last
175 \&\fIBN_CTX_get()\fR call. In case of an error, an error code is set, which
176 can be obtained by \fIERR_get_error\fR\|(3).
178 .IX Header "SEE ALSO"
179 \&\fIBN_CTX_new\fR\|(3)
182 \&\fIBN_CTX_start()\fR, \fIBN_CTX_get()\fR and \fIBN_CTX_end()\fR were added in OpenSSL 0.9.5.