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[dragonfly.git] / secure / lib / libcrypto / man / BN_mod_mul_reciprocal.3
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80.\" If the F register is turned on, we'll generate
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96.TH BN_mod_mul_reciprocal 3 "0.9.7d" "2/Sep/2004" "OpenSSL"
97.UC
98.if n .hy 0
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190.SH "NAME"
191BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
192BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using
193reciprocal
194.SH "SYNOPSIS"
74dab6c2 195.PP
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196.Vb 1
197\& #include <openssl/bn.h>
198.Ve
199.Vb 3
200\& BN_RECP_CTX *BN_RECP_CTX_new(void);
201\& void BN_RECP_CTX_init(BN_RECP_CTX *recp);
202\& void BN_RECP_CTX_free(BN_RECP_CTX *recp);
203.Ve
204.Vb 1
205\& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
206.Ve
207.Vb 2
208\& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
209\& BN_CTX *ctx);
210.Ve
211.Vb 2
212\& int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
213\& BN_RECP_CTX *recp, BN_CTX *ctx);
214.Ve
215.SH "DESCRIPTION"
74dab6c2 216\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient
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217BN_mod_mul(3) operation when the operation will be performed
218repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR
219using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a
74dab6c2 220previously allocated \fBBN_CTX\fR used for temporary variables.
984263bc 221.PP
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222\fIBN_RECP_CTX_new()\fR allocates and initializes a \fBBN_RECP\fR structure.
223\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fBBN_RECP\fR.
984263bc 224.PP
74dab6c2 225\fIBN_RECP_CTX_free()\fR frees the components of the \fBBN_RECP\fR, and, if it
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226was created by \fIBN_RECP_CTX_new()\fR, also the structure itself.
227.PP
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228\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing
2291/\fBm\fR and shifting it left by \fIBN_num_bits\fR\|(\fBm\fR)+1 to make it an
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230integer. The result and the number of bits it was shifted left will
231later be stored in \fBrecp\fR.
232.PP
74dab6c2 233\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient
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234in \fBdv\fR and the remainder in \fBrem\fR.
235.PP
74dab6c2 236The \fBBN_RECP_CTX\fR structure is defined as follows:
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237.PP
238.Vb 8
239\& typedef struct bn_recp_ctx_st
240\& {
241\& BIGNUM N; /* the divisor */
242\& BIGNUM Nr; /* the reciprocal */
243\& int num_bits;
244\& int shift;
245\& int flags;
246\& } BN_RECP_CTX;
247.Ve
248It cannot be shared between threads.
249.SH "RETURN VALUES"
74dab6c2 250\fIBN_RECP_CTX_new()\fR returns the newly allocated \fBBN_RECP_CTX\fR, and NULL
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251on error.
252.PP
74dab6c2 253\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values.
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254.PP
255For the other functions, 1 is returned for success, 0 on error.
256The error codes can be obtained by ERR_get_error(3).
257.SH "SEE ALSO"
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258bn(3), ERR_get_error(3), BN_add(3),
259BN_CTX_new(3)
260.SH "HISTORY"
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261\fBBN_RECP_CTX\fR was added in SSLeay 0.9.0. Before that, the function
262\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR
984263bc 263arguments were different.
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264
265.rn }` ''
266.IX Title "BN_mod_mul_reciprocal 3"
267.IX Name "BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
268BN_RECP_CTX_free, BN_RECP_CTX_set - modular multiplication using
269reciprocal"
270
271.IX Header "NAME"
272
273.IX Header "SYNOPSIS"
274
275.IX Header "DESCRIPTION"
276
277.IX Header "RETURN VALUES"
278
279.IX Header "SEE ALSO"
280
281.IX Header "HISTORY"
282