Edit File: BN_sub.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" BN_add, BN_sub, BN_mul, BN_sqr, BN_div, BN_mod, BN_nnmod, BN_mod_add, BN_mod_sub, BN_mod_mul, BN_mod_sqr, BN_exp, BN_mod_exp, BN_gcd \- arithmetic operations on BIGNUMs .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/bn.h> \& \& int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b); \& \& int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b); \& \& int BN_mul(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_CTX *ctx); \& \& int BN_sqr(BIGNUM *r, BIGNUM *a, BN_CTX *ctx); \& \& int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *a, const BIGNUM *d, \& BN_CTX *ctx); \& \& int BN_mod(BIGNUM *rem, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx); \& \& int BN_nnmod(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx); \& \& int BN_mod_add(BIGNUM *r, BIGNUM *a, BIGNUM *b, const BIGNUM *m, \& BN_CTX *ctx); \& \& int BN_mod_sub(BIGNUM *r, BIGNUM *a, BIGNUM *b, const BIGNUM *m, \& BN_CTX *ctx); \& \& int BN_mod_mul(BIGNUM *r, BIGNUM *a, BIGNUM *b, const BIGNUM *m, \& BN_CTX *ctx); \& \& int BN_mod_sqr(BIGNUM *r, BIGNUM *a, const BIGNUM *m, BN_CTX *ctx); \& \& int BN_exp(BIGNUM *r, BIGNUM *a, BIGNUM *p, BN_CTX *ctx); \& \& int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p, \& const BIGNUM *m, BN_CTX *ctx); \& \& int BN_gcd(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_CTX *ctx); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBBN_add()\fR adds \fIa\fR and \fIb\fR and places the result in \fIr\fR (\f(CW\*(C`r=a+b\*(C'\fR). \&\fIr\fR may be the same \fB\s-1BIGNUM\s0\fR as \fIa\fR or \fIb\fR. .PP \&\fBBN_sub()\fR subtracts \fIb\fR from \fIa\fR and places the result in \fIr\fR (\f(CW\*(C`r=a\-b\*(C'\fR). .PP \&\fBBN_mul()\fR multiplies \fIa\fR and \fIb\fR and places the result in \fIr\fR (\f(CW\*(C`r=a*b\*(C'\fR). \&\fIr\fR may be the same \fB\s-1BIGNUM\s0\fR as \fIa\fR or \fIb\fR. For multiplication by powers of 2, use \fBBN_lshift\fR\|(3). .PP \&\fBBN_sqr()\fR takes the square of \fIa\fR and places the result in \fIr\fR (\f(CW\*(C`r=a^2\*(C'\fR). \fIr\fR and \fIa\fR may be the same \fB\s-1BIGNUM\s0\fR. This function is faster than BN_mul(r,a,a). .PP \&\fBBN_div()\fR divides \fIa\fR by \fId\fR and places the result in \fIdv\fR and the remainder in \fIrem\fR (\f(CW\*(C`dv=a/d, rem=a%d\*(C'\fR). Either of \fIdv\fR and \fIrem\fR may be \fB\s-1NULL\s0\fR, in which case the respective value is not returned. The result is rounded towards zero; thus if \fIa\fR is negative, the remainder will be zero or negative. For division by powers of 2, use \fBBN_rshift\fR\|(3). .PP \&\fBBN_mod()\fR corresponds to \fBBN_div()\fR with \fIdv\fR set to \fB\s-1NULL\s0\fR. .PP \&\fBBN_nnmod()\fR reduces \fIa\fR modulo \fIm\fR and places the non-negative remainder in \fIr\fR. .PP \&\fBBN_mod_add()\fR adds \fIa\fR to \fIb\fR modulo \fIm\fR and places the non-negative result in \fIr\fR. .PP \&\fBBN_mod_sub()\fR subtracts \fIb\fR from \fIa\fR modulo \fIm\fR and places the non-negative result in \fIr\fR. .PP \&\fBBN_mod_mul()\fR multiplies \fIa\fR by \fIb\fR and finds the non-negative remainder respective to modulus \fIm\fR (\f(CW\*(C`r=(a*b) mod m\*(C'\fR). \fIr\fR may be the same \fB\s-1BIGNUM\s0\fR as \fIa\fR or \fIb\fR. For more efficient algorithms for repeated computations using the same modulus, see \&\fBBN_mod_mul_montgomery\fR\|(3) and \&\fBBN_mod_mul_reciprocal\fR\|(3). .PP \&\fBBN_mod_sqr()\fR takes the square of \fIa\fR modulo \fBm\fR and places the result in \fIr\fR. .PP \&\fBBN_exp()\fR raises \fIa\fR to the \fIp\fR\-th power and places the result in \fIr\fR (\f(CW\*(C`r=a^p\*(C'\fR). This function is faster than repeated applications of \&\fBBN_mul()\fR. .PP \&\fBBN_mod_exp()\fR computes \fIa\fR to the \fIp\fR\-th power modulo \fIm\fR (\f(CW\*(C`r=a^p % m\*(C'\fR). This function uses less time and space than \fBBN_exp()\fR. Do not call this function when \fBm\fR is even and any of the parameters have the \&\fB\s-1BN_FLG_CONSTTIME\s0\fR flag set. .PP \&\fBBN_gcd()\fR computes the greatest common divisor of \fIa\fR and \fIb\fR and places the result in \fIr\fR. \fIr\fR may be the same \fB\s-1BIGNUM\s0\fR as \fIa\fR or \&\fIb\fR. .PP For all functions, \fIctx\fR is a previously allocated \fB\s-1BN_CTX\s0\fR used for temporary variables; see \fBBN_CTX_new\fR\|(3). .PP Unless noted otherwise, the result \fB\s-1BIGNUM\s0\fR must be different from the arguments. .SH "RETURN VALUES" .IX Header "RETURN VALUES" For all functions, 1 is returned for success, 0 on error. The return value should always be checked (e.g., \f(CW\*(C`if (!BN_add(r,a,b)) goto err;\*(C'\fR). The error codes can be obtained by \fBERR_get_error\fR\|(3). .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBbn\fR\|(3), \fBERR_get_error\fR\|(3), \fBBN_CTX_new\fR\|(3), \&\fBBN_add_word\fR\|(3), \fBBN_set_bit\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" \&\fBBN_add()\fR, \fBBN_sub()\fR, \fBBN_sqr()\fR, \fBBN_div()\fR, \fBBN_mod()\fR, \fBBN_mod_mul()\fR, \&\fBBN_mod_exp()\fR and \fBBN_gcd()\fR are available in all versions of SSLeay and OpenSSL. The \fIctx\fR argument to \fBBN_mul()\fR was added in SSLeay 0.9.1b. \fBBN_exp()\fR appeared in SSLeay 0.9.0. \&\fBBN_nnmod()\fR, \fBBN_mod_add()\fR, \fBBN_mod_sub()\fR, and \fBBN_mod_sqr()\fR were added in OpenSSL 0.9.7.