Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / BN_mod_mul_reciprocal.3
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124.\" ========================================================================
125.\"
126.IX Title "BN_mod_mul_reciprocal 3"
e3261593 127.TH BN_mod_mul_reciprocal 3 "2012-01-04" "1.0.0f" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
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132.SH "NAME"
133BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
134BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using
135reciprocal
136.SH "SYNOPSIS"
8b0cefbb 137.IX Header "SYNOPSIS"
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138.Vb 1
139\& #include <openssl/bn.h>
e257b235 140\&
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141\& BN_RECP_CTX *BN_RECP_CTX_new(void);
142\& void BN_RECP_CTX_init(BN_RECP_CTX *recp);
143\& void BN_RECP_CTX_free(BN_RECP_CTX *recp);
e257b235 144\&
984263bc 145\& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
e257b235 146\&
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147\& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
148\& BN_CTX *ctx);
e257b235 149\&
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150\& int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
151\& BN_RECP_CTX *recp, BN_CTX *ctx);
152.Ve
153.SH "DESCRIPTION"
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154.IX Header "DESCRIPTION"
155\&\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient
156\&\fIBN_mod_mul\fR\|(3) operation when the operation will be performed
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157repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR
158using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a
8b0cefbb 159previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables.
984263bc 160.PP
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161\&\fIBN_RECP_CTX_new()\fR allocates and initializes a \fB\s-1BN_RECP\s0\fR structure.
162\&\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_RECP\s0\fR.
984263bc 163.PP
8b0cefbb 164\&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it
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165was created by \fIBN_RECP_CTX_new()\fR, also the structure itself.
166.PP
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167\&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing
1681/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+1 to make it an
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169integer. The result and the number of bits it was shifted left will
170later be stored in \fBrecp\fR.
171.PP
8b0cefbb 172\&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient
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173in \fBdv\fR and the remainder in \fBrem\fR.
174.PP
8b0cefbb 175The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows:
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176.PP
177.Vb 8
178\& typedef struct bn_recp_ctx_st
179\& {
180\& BIGNUM N; /* the divisor */
181\& BIGNUM Nr; /* the reciprocal */
182\& int num_bits;
183\& int shift;
184\& int flags;
185\& } BN_RECP_CTX;
186.Ve
8b0cefbb 187.PP
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188It cannot be shared between threads.
189.SH "RETURN VALUES"
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190.IX Header "RETURN VALUES"
191\&\fIBN_RECP_CTX_new()\fR returns the newly allocated \fB\s-1BN_RECP_CTX\s0\fR, and \s-1NULL\s0
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192on error.
193.PP
8b0cefbb 194\&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values.
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195.PP
196For the other functions, 1 is returned for success, 0 on error.
8b0cefbb 197The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 198.SH "SEE ALSO"
74dab6c2 199.IX Header "SEE ALSO"
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200\&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIBN_add\fR\|(3),
201\&\fIBN_CTX_new\fR\|(3)
202.SH "HISTORY"
74dab6c2 203.IX Header "HISTORY"
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204\&\fB\s-1BN_RECP_CTX\s0\fR was added in SSLeay 0.9.0. Before that, the function
205\&\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR
206arguments were different.