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[dragonfly.git] / secure / lib / libcrypto / man / BN_mod_mul_reciprocal.3
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129.\" ========================================================================
130.\"
131.IX Title "BN_mod_mul_reciprocal 3"
aac4ff6f 132.TH BN_mod_mul_reciprocal 3 "2008-09-06" "0.9.8h" "OpenSSL"
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133.SH "NAME"
134BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
135BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using
136reciprocal
137.SH "SYNOPSIS"
8b0cefbb 138.IX Header "SYNOPSIS"
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139.Vb 1
140\& #include <openssl/bn.h>
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141.Ve
142.PP
143.Vb 3
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144\& BN_RECP_CTX *BN_RECP_CTX_new(void);
145\& void BN_RECP_CTX_init(BN_RECP_CTX *recp);
146\& void BN_RECP_CTX_free(BN_RECP_CTX *recp);
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147.Ve
148.PP
149.Vb 1
984263bc 150\& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
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151.Ve
152.PP
153.Vb 2
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154\& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
155\& BN_CTX *ctx);
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156.Ve
157.PP
158.Vb 2
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159\& int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
160\& BN_RECP_CTX *recp, BN_CTX *ctx);
161.Ve
162.SH "DESCRIPTION"
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163.IX Header "DESCRIPTION"
164\&\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient
165\&\fIBN_mod_mul\fR\|(3) operation when the operation will be performed
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166repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR
167using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a
8b0cefbb 168previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables.
984263bc 169.PP
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170\&\fIBN_RECP_CTX_new()\fR allocates and initializes a \fB\s-1BN_RECP\s0\fR structure.
171\&\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_RECP\s0\fR.
984263bc 172.PP
8b0cefbb 173\&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it
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174was created by \fIBN_RECP_CTX_new()\fR, also the structure itself.
175.PP
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176\&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing
1771/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+1 to make it an
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178integer. The result and the number of bits it was shifted left will
179later be stored in \fBrecp\fR.
180.PP
8b0cefbb 181\&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient
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182in \fBdv\fR and the remainder in \fBrem\fR.
183.PP
8b0cefbb 184The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows:
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185.PP
186.Vb 8
187\& typedef struct bn_recp_ctx_st
188\& {
189\& BIGNUM N; /* the divisor */
190\& BIGNUM Nr; /* the reciprocal */
191\& int num_bits;
192\& int shift;
193\& int flags;
194\& } BN_RECP_CTX;
195.Ve
8b0cefbb 196.PP
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197It cannot be shared between threads.
198.SH "RETURN VALUES"
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199.IX Header "RETURN VALUES"
200\&\fIBN_RECP_CTX_new()\fR returns the newly allocated \fB\s-1BN_RECP_CTX\s0\fR, and \s-1NULL\s0
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201on error.
202.PP
8b0cefbb 203\&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values.
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204.PP
205For the other functions, 1 is returned for success, 0 on error.
8b0cefbb 206The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 207.SH "SEE ALSO"
74dab6c2 208.IX Header "SEE ALSO"
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209\&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIBN_add\fR\|(3),
210\&\fIBN_CTX_new\fR\|(3)
211.SH "HISTORY"
74dab6c2 212.IX Header "HISTORY"
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213\&\fB\s-1BN_RECP_CTX\s0\fR was added in SSLeay 0.9.0. Before that, the function
214\&\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR
215arguments were different.