BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables
void BN_CTX_start(BN_CTX *ctx);
BIGNUM *BN_CTX_get(BN_CTX *ctx);
void BN_CTX_end(BN_CTX *ctx);
These functions are used to obtain temporary BIGNUM variables from a BN_CTX (which can been created by using BN_CTX_new(3)) in order to save the overhead of repeatedly creating and freeing BIGNUMs 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 BIGNUMs. All
BN_CTX_get() calls must be made before calling any
other functions that use the
ctx as an argument.
BN_CTX_end() must be called before returning from the
BN_CTX_end() is called, the BIGNUM pointers obtained from
BN_CTX_get() become invalid.
BN_CTX_end() return no values.
BN_CTX_get() returns a pointer to the BIGNUM, or NULL on error. Once
BN_CTX_get() has failed, the subsequent calls
will return 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 ERR_get_error(3).
BN_CTX_end() were added in OpenSSL 0.9.5.