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RedHat 9 (Linux i386) - man page for bn_ctx_start (redhat section 3)

BN_CTX_start(3) 						      OpenSSL							   BN_CTX_start(3)

NAME
BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables
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);
DESCRIPTION
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. Finally, BN_CTX_end() must be called before returning from the function. When BN_CTX_end() is called, the BIGNUM pointers obtained from BN_CTX_get() become invalid.
RETURN VALUES
BN_CTX_start() and 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).
SEE ALSO
BN_CTX_new(3)
HISTORY
BN_CTX_start(), BN_CTX_get() and BN_CTX_end() were added in OpenSSL 0.9.5. 0.9.7a 2000-07-11 BN_CTX_start(3)