#include
void BN_CTX_start(BN_CTX *ctx);
BIGNUM *BN_CTX_get(BN_CTX *ctx);
void BN_CTX_end(BN_CTX *ctx);
A function must call _B_N___C_T_X___s_t_a_r_t_(_) first. Then, _B_N___C_T_X___g_e_t_(_) may be called repeatedly to obtain temporary BBIIGGNNUUMMs. All _B_N___C_T_X___g_e_t_(_) calls must be made before calling any other functions that use the ccttxx as an argument.
Finally, _B_N___C_T_X___e_n_d_(_) must be called before returning from the function. When _B_N___C_T_X___e_n_d_(_) is called, the BBIIGGNNUUMM pointers obtained from _B_N___C_T_X___g_e_t_(_) become invalid.
_B_N___C_T_X___g_e_t_(_) returns a pointer to the BBIIGGNNUUMM, or NNUULLLL on error. Once _B_N___C_T_X___g_e_t_(_) has failed, the subsequent calls will return NNUULLLL as well, so it is sufficient to check the return value of the last _B_N___C_T_X___g_e_t_(_) call. In case of an error, an error code is set, which can be obtained by _E_R_R___g_e_t___e_r_r_o_r(3).