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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init, BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using reciprocal .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include \& \& BN_RECP_CTX *BN_RECP_CTX_new(void); \& void BN_RECP_CTX_init(BN_RECP_CTX *recp); \& void BN_RECP_CTX_free(BN_RECP_CTX *recp); \& \& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx); \& \& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp, \& BN_CTX *ctx); \& \& int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b, \& BN_RECP_CTX *recp, BN_CTX *ctx); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient \&\fIBN_mod_mul\fR\|(3) operation when the operation will be performed repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables. .PP \&\fIBN_RECP_CTX_new()\fR allocates and initializes a \fB\s-1BN_RECP\s0\fR structure. \&\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_RECP\s0\fR. .PP \&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it was created by \fIBN_RECP_CTX_new()\fR, also the structure itself. .PP \&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing 1/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+1 to make it an integer. The result and the number of bits it was shifted left will later be stored in \fBrecp\fR. .PP \&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient in \fBdv\fR and the remainder in \fBrem\fR. .PP The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows: .PP .Vb 8 \& typedef struct bn_recp_ctx_st \& { \& BIGNUM N; /* the divisor */ \& BIGNUM Nr; /* the reciprocal */ \& int num_bits; \& int shift; \& int flags; \& } BN_RECP_CTX; .Ve .PP It cannot be shared between threads. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fIBN_RECP_CTX_new()\fR returns the newly allocated \fB\s-1BN_RECP_CTX\s0\fR, and \s-1NULL\s0 on error. .PP \&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values. .PP For the other functions, 1 is returned for success, 0 on error. The error codes can be obtained by \fIERR_get_error\fR\|(3). .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIBN_add\fR\|(3), \&\fIBN_CTX_new\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" \&\fB\s-1BN_RECP_CTX\s0\fR was added in SSLeay 0.9.0. Before that, the function \&\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR arguments were different.