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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.

1.0.2h                            2016-05-03                   BN_CTX_start(3)