BNmodmulreciprocal(3) OpenSSL BNmodmulreciprocal(3)

NAME
       BNmodmulreciprocal,  BNdivrecp, BNRECPCTXnew, BNRECPCTXinit,
       BNRECPCTXfree, BNRECPCTXset - modular multiplication using
       reciprocal

SYNOPSIS
        #include 

        BNRECPCTX *BNRECPCTXnew(void);
        void BNRECPCTXinit(BNRECPCTX *recp);
        void BNRECPCTXfree(BNRECPCTX *recp);

        int BNRECPCTXset(BNRECPCTX *recp, const BIGNUM *m, BNCTX *ctx);

        int BNdivrecp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BNRECPCTX *recp,
               BNCTX *ctx);

        int BNmodmulreciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
               BNRECPCTX *recp, BNCTX *ctx);

DESCRIPTION
       BNmodmulreciprocal() can be used to perform an efficient
       BNmodmul(3) operation when the operation will be performed repeatedly
       with the same modulus. It computes rr=(aa*bb)%mm using rreeccpp=1/mm, which is
       set as described below.  ccttxx is a previously allocated BBNNCCTTXX used for
       temporary variables.

       BNRECPCTXnew() allocates and initializes a BBNNRREECCPP structure.
       BNRECPCTXinit() initializes an existing uninitialized BBNNRREECCPP.

       BNRECPCTXfree() frees the components of the BBNNRREECCPP, and, if it was
       created by BNRECPCTXnew(), also the structure itself.

       BNRECPCTXset() stores mm in rreeccpp and sets it up for computing 1/mm and
       shifting it left by BNnumbits(mm)+1 to make it an integer. The result
       and the number of bits it was shifted left will later be stored in
       rreeccpp.

       BNdivrecp() divides aa by mm using rreeccpp. It places the quotient in ddvv
       and the remainder in rreemm.

       The BBNNRREECCPPCCTTXX structure is defined as follows:

        typedef struct bnrecpctxst
               {
               BIGNUM N;       /* the divisor */
               BIGNUM Nr;      /* the reciprocal */
               int numbits;
               int shift;
               int flags;
               } BNRECPCTX;

       It cannot be shared between threads.

RETURN VALUES
       BNRECPCTXnew() returns the newly allocated BBNNRREECCPPCCTTXX, and NULL on
       error.

       BNRECPCTXinit() and BNRECPCTXfree() have no return values.

       For the other functions, 1 is returned for success, 0 on error.  The
       error codes can be obtained by ERRgeterror(3).

SEE ALSO
       bn(3), ERRgeterror(3), BNadd(3), BNCTXnew(3)

HISTORY       BBNNRREECCPPCCTTXX was added in SSLeay 0.9.0. Before that, the function
       BNreciprocal() was used instead, and the BNmodmulreciprocal()
       arguments were different.



0.9.7l                            2002-09-25          BNmodmulreciprocal(3)