1.\" Automatically generated by Pod::Man version 1.15
2.\" Tue Jul 30 09:21:21 2002
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138.\" ======================================================================
139.\"
140.IX Title "BN_mod_mul_reciprocal 3"
141.TH BN_mod_mul_reciprocal 3 "0.9.6e" "2000-11-12" "OpenSSL"
142.UC
143.SH "NAME"
144BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
145BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using
146reciprocal
147.SH "SYNOPSIS"
148.IX Header "SYNOPSIS"
149.Vb 1
150\& #include <openssl/bn.h>
151.Ve
152.Vb 3
153\& BN_RECP_CTX *BN_RECP_CTX_new(void);
154\& void BN_RECP_CTX_init(BN_RECP_CTX *recp);
155\& void BN_RECP_CTX_free(BN_RECP_CTX *recp);
156.Ve
157.Vb 1
158\& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
159.Ve
160.Vb 2
161\& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
162\& BN_CTX *ctx);
163.Ve
164.Vb 2
165\& int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
166\& BN_RECP_CTX *recp, BN_CTX *ctx);
167.Ve
168.SH "DESCRIPTION"
169.IX Header "DESCRIPTION"
170\&\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient
171BN_mod_mul(3) operation when the operation will be performed
172repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR
173using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a
174previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables.
175.PP
176\&\fIBN_RECP_CTX_new()\fR allocates and initializes a \fB\s-1BN_RECP\s0\fR structure.
177\&\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_RECP\s0\fR.
178.PP
179\&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it
180was created by \fIBN_RECP_CTX_new()\fR, also the structure itself.
181.PP
182\&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing
1831/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+1 to make it an
184integer. The result and the number of bits it was shifted left will
185later be stored in \fBrecp\fR.
186.PP
187\&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient
188in \fBdv\fR and the remainder in \fBrem\fR.
189.PP
190The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows:
191.PP
192.Vb 8
193\& typedef struct bn_recp_ctx_st
194\& {
195\& BIGNUM N; /* the divisor */
196\& BIGNUM Nr; /* the reciprocal */
197\& int num_bits;
198\& int shift;
199\& int flags;
200\& } BN_RECP_CTX;
201.Ve
202It cannot be shared between threads.
203.SH "RETURN VALUES"
204.IX Header "RETURN VALUES"
205\&\fIBN_RECP_CTX_new()\fR returns the newly allocated \fB\s-1BN_RECP_CTX\s0\fR, and \s-1NULL\s0
206on error.
207.PP
208\&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values.
209.PP
210For the other functions, 1 is returned for success, 0 on error.
211The error codes can be obtained by ERR_get_error(3).
212.SH "SEE ALSO"
213.IX Header "SEE ALSO"
214bn(3), err(3), BN_add(3),
215BN_CTX_new(3)
216.SH "HISTORY"
217.IX Header "HISTORY"
218\&\fB\s-1BN_RECP_CTX\s0\fR was added in SSLeay 0.9.0. Before that, the function
219\&\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR
220arguments were different.
2.\" Tue Jul 30 09:21:21 2002
3.\"
4.\" Standard preamble:
5.\" ======================================================================
6.de Sh \" Subsection heading
7.br
8.if t .Sp
9.ne 5
10.PP
11\fB\\$1\fR
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14.de Sp \" Vertical space (when we can't use .PP)
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17..
18.de Ip \" List item
19.br
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21.el .ne 3
22.IP "\\$1" \\$2
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24.de Vb \" Begin verbatim text
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34.\" Set up some character translations and predefined strings. \*(-- will
35.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
36.\" double quote, and \*(R" will give a right double quote. | will give a
37.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used
38.\" to do unbreakable dashes and therefore won't be available. \*(C` and
39.\" \*(C' expand to `' in nroff, nothing in troff, for use with C<>
40.tr \(*W-|\(bv\*(Tr
41.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
42.ie n \{\
43. ds -- \(*W-
44. ds PI pi
45. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
46. if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
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51'br\}
52.el\{\
53. ds -- \|\(em\|
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57'br\}
58.\"
59.\" If the F register is turned on, we'll generate index entries on stderr
60.\" for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and
61.\" index entries marked with X<> in POD. Of course, you'll have to process
62.\" the output yourself in some meaningful fashion.
63.if \nF \{\
64. de IX
65. tm Index:\\$1\t\\n%\t"\\$2"
66..
67. nr % 0
68. rr F
69.\}
70.\"
71.\" For nroff, turn off justification. Always turn off hyphenation; it
72.\" makes way too many mistakes in technical documents.
73.hy 0
74.if n .na
75.\"
76.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
77.\" Fear. Run. Save yourself. No user-serviceable parts.
78.bd B 3
79. \" fudge factors for nroff and troff
80.if n \{\
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137.rm #[ #] #H #V #F C
138.\" ======================================================================
139.\"
140.IX Title "BN_mod_mul_reciprocal 3"
141.TH BN_mod_mul_reciprocal 3 "0.9.6e" "2000-11-12" "OpenSSL"
142.UC
143.SH "NAME"
144BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
145BN_RECP_CTX_free, BN_RECP_CTX_set \- modular multiplication using
146reciprocal
147.SH "SYNOPSIS"
148.IX Header "SYNOPSIS"
149.Vb 1
150\& #include <openssl/bn.h>
151.Ve
152.Vb 3
153\& BN_RECP_CTX *BN_RECP_CTX_new(void);
154\& void BN_RECP_CTX_init(BN_RECP_CTX *recp);
155\& void BN_RECP_CTX_free(BN_RECP_CTX *recp);
156.Ve
157.Vb 1
158\& int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
159.Ve
160.Vb 2
161\& int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
162\& BN_CTX *ctx);
163.Ve
164.Vb 2
165\& int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
166\& BN_RECP_CTX *recp, BN_CTX *ctx);
167.Ve
168.SH "DESCRIPTION"
169.IX Header "DESCRIPTION"
170\&\fIBN_mod_mul_reciprocal()\fR can be used to perform an efficient
171BN_mod_mul(3) operation when the operation will be performed
172repeatedly with the same modulus. It computes \fBr\fR=(\fBa\fR*\fBb\fR)%\fBm\fR
173using \fBrecp\fR=1/\fBm\fR, which is set as described below. \fBctx\fR is a
174previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables.
175.PP
176\&\fIBN_RECP_CTX_new()\fR allocates and initializes a \fB\s-1BN_RECP\s0\fR structure.
177\&\fIBN_RECP_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_RECP\s0\fR.
178.PP
179\&\fIBN_RECP_CTX_free()\fR frees the components of the \fB\s-1BN_RECP\s0\fR, and, if it
180was created by \fIBN_RECP_CTX_new()\fR, also the structure itself.
181.PP
182\&\fIBN_RECP_CTX_set()\fR stores \fBm\fR in \fBrecp\fR and sets it up for computing
1831/\fBm\fR and shifting it left by BN_num_bits(\fBm\fR)+1 to make it an
184integer. The result and the number of bits it was shifted left will
185later be stored in \fBrecp\fR.
186.PP
187\&\fIBN_div_recp()\fR divides \fBa\fR by \fBm\fR using \fBrecp\fR. It places the quotient
188in \fBdv\fR and the remainder in \fBrem\fR.
189.PP
190The \fB\s-1BN_RECP_CTX\s0\fR structure is defined as follows:
191.PP
192.Vb 8
193\& typedef struct bn_recp_ctx_st
194\& {
195\& BIGNUM N; /* the divisor */
196\& BIGNUM Nr; /* the reciprocal */
197\& int num_bits;
198\& int shift;
199\& int flags;
200\& } BN_RECP_CTX;
201.Ve
202It cannot be shared between threads.
203.SH "RETURN VALUES"
204.IX Header "RETURN VALUES"
205\&\fIBN_RECP_CTX_new()\fR returns the newly allocated \fB\s-1BN_RECP_CTX\s0\fR, and \s-1NULL\s0
206on error.
207.PP
208\&\fIBN_RECP_CTX_init()\fR and \fIBN_RECP_CTX_free()\fR have no return values.
209.PP
210For the other functions, 1 is returned for success, 0 on error.
211The error codes can be obtained by ERR_get_error(3).
212.SH "SEE ALSO"
213.IX Header "SEE ALSO"
214bn(3), err(3), BN_add(3),
215BN_CTX_new(3)
216.SH "HISTORY"
217.IX Header "HISTORY"
218\&\fB\s-1BN_RECP_CTX\s0\fR was added in SSLeay 0.9.0. Before that, the function
219\&\fIBN_reciprocal()\fR was used instead, and the \fIBN_mod_mul_reciprocal()\fR
220arguments were different.