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| 132 | .\" ======================================================================== |
| 133 | .\" |
| 134 | .IX Title "BN_mod_mul_reciprocal 3" |
| 135 | .TH BN_mod_mul_reciprocal 3 "2009-01-11" "0.9.8j" "OpenSSL" |
| 136 | .\" For nroff, turn off justification. Always turn off hyphenation; it makes |
| 137 | .\" way too many mistakes in technical documents. |
| 138 | .if n .ad l |
| 139 | .nh |
| 140 | .SH "NAME" |
| 141 | BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init, |
| 142 | BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using |
| 143 | reciprocal |
| 144 | .SH "SYNOPSIS" |
| 145 | .IX Header "SYNOPSIS" |
| 146 | .Vb 1 |
| 147 | \& #include <openssl/bn.h> |
| 148 | \& |
| 149 | \& BN_RECP_CTX *BN_RECP_CTX_new(void); |
| 150 | \& void BN_RECP_CTX_init(BN_RECP_CTX *recp); |
| 151 | \& void BN_RECP_CTX_free(BN_RECP_CTX *recp); |
| 152 | \& |
| 153 | \& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx); |
| 154 | \& |
| 155 | \& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp, |
| 156 | \& BN_CTX *ctx); |
| 157 | \& |
| 158 | \& int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b, |
| 159 | \& BN_RECP_CTX *recp, BN_CTX *ctx); |
| 160 | .Ve |
| 161 | .SH "DESCRIPTION" |
| 162 | .IX Header "DESCRIPTION" |
| 163 | \&\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient |
| 164 | \&\fIBN_mod_mul\fR\|(3) operation when the operation will be performed |
| 165 | repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR |
| 166 | using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a |
| 167 | previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables. |
| 168 | .PP |
| 169 | \&\fIBN_RECP_CTX_new()\fR allocates and initializes a \fB\s-1BN_RECP\s0\fR structure. |
| 170 | \&\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_RECP\s0\fR. |
| 171 | .PP |
| 172 | \&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it |
| 173 | was created by \fIBN_RECP_CTX_new()\fR, also the structure itself. |
| 174 | .PP |
| 175 | \&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing |
| 176 | 1/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+1 to make it an |
| 177 | integer. The result and the number of bits it was shifted left will |
| 178 | later be stored in \fBrecp\fR. |
| 179 | .PP |
| 180 | \&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient |
| 181 | in \fBdv\fR and the remainder in \fBrem\fR. |
| 182 | .PP |
| 183 | The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows: |
| 184 | .PP |
| 185 | .Vb 8 |
| 186 | \& typedef struct bn_recp_ctx_st |
| 187 | \& { |
| 188 | \& BIGNUM N; /* the divisor */ |
| 189 | \& BIGNUM Nr; /* the reciprocal */ |
| 190 | \& int num_bits; |
| 191 | \& int shift; |
| 192 | \& int flags; |
| 193 | \& } BN_RECP_CTX; |
| 194 | .Ve |
| 195 | .PP |
| 196 | It cannot be shared between threads. |
| 197 | .SH "RETURN VALUES" |
| 198 | .IX Header "RETURN VALUES" |
| 199 | \&\fIBN_RECP_CTX_new()\fR returns the newly allocated \fB\s-1BN_RECP_CTX\s0\fR, and \s-1NULL\s0 |
| 200 | on error. |
| 201 | .PP |
| 202 | \&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values. |
| 203 | .PP |
| 204 | For the other functions, 1 is returned for success, 0 on error. |
| 205 | The error codes can be obtained by \fIERR_get_error\fR\|(3). |
| 206 | .SH "SEE ALSO" |
| 207 | .IX Header "SEE ALSO" |
| 208 | \&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIBN_add\fR\|(3), |
| 209 | \&\fIBN_CTX_new\fR\|(3) |
| 210 | .SH "HISTORY" |
| 211 | .IX Header "HISTORY" |
| 212 | \&\fB\s-1BN_RECP_CTX\s0\fR was added in SSLeay 0.9.0. Before that, the function |
| 213 | \&\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR |
| 214 | arguments were different. |