Update build for OpenSSL-0.9.8j upgrade.
[dragonfly.git] / secure / lib / libcrypto / man / BN_mod_mul_reciprocal.3
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132.\" ========================================================================
133.\"
134.IX Title "BN_mod_mul_reciprocal 3"
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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
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140.SH "NAME"
141BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
142BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using
143reciprocal
144.SH "SYNOPSIS"
8b0cefbb 145.IX Header "SYNOPSIS"
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146.Vb 1
147\& #include <openssl/bn.h>
e257b235 148\&
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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);
e257b235 152\&
984263bc 153\& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
e257b235 154\&
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155\& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
156\& BN_CTX *ctx);
e257b235 157\&
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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"
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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
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165repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR
166using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a
8b0cefbb 167previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables.
984263bc 168.PP
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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.
984263bc 171.PP
8b0cefbb 172\&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it
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173was created by \fIBN_RECP_CTX_new()\fR, also the structure itself.
174.PP
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175\&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing
1761/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+1 to make it an
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177integer. The result and the number of bits it was shifted left will
178later be stored in \fBrecp\fR.
179.PP
8b0cefbb 180\&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient
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181in \fBdv\fR and the remainder in \fBrem\fR.
182.PP
8b0cefbb 183The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows:
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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
8b0cefbb 195.PP
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196It cannot be shared between threads.
197.SH "RETURN VALUES"
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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
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200on error.
201.PP
8b0cefbb 202\&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values.
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203.PP
204For the other functions, 1 is returned for success, 0 on error.
8b0cefbb 205The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 206.SH "SEE ALSO"
74dab6c2 207.IX Header "SEE ALSO"
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208\&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIBN_add\fR\|(3),
209\&\fIBN_CTX_new\fR\|(3)
210.SH "HISTORY"
74dab6c2 211.IX Header "HISTORY"
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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
214arguments were different.