diff options
Diffstat (limited to 'libtommath/bn_mp_jacobi.c')
-rw-r--r-- | libtommath/bn_mp_jacobi.c | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/libtommath/bn_mp_jacobi.c b/libtommath/bn_mp_jacobi.c new file mode 100644 index 0000000..c87ab88 --- /dev/null +++ b/libtommath/bn_mp_jacobi.c @@ -0,0 +1,105 @@ +#include <tommath.h> +#ifdef BN_MP_JACOBI_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis + * + * LibTomMath is a library that provides multiple-precision + * integer arithmetic as well as number theoretic functionality. + * + * The library was designed directly after the MPI library by + * Michael Fromberger but has been written from scratch with + * additional optimizations in place. + * + * The library is free for all purposes without any express + * guarantee it works. + * + * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org + */ + +/* computes the jacobi c = (a | n) (or Legendre if n is prime) + * HAC pp. 73 Algorithm 2.149 + */ +int mp_jacobi (mp_int * a, mp_int * p, int *c) +{ + mp_int a1, p1; + int k, s, r, res; + mp_digit residue; + + /* if p <= 0 return MP_VAL */ + if (mp_cmp_d(p, 0) != MP_GT) { + return MP_VAL; + } + + /* step 1. if a == 0, return 0 */ + if (mp_iszero (a) == 1) { + *c = 0; + return MP_OKAY; + } + + /* step 2. if a == 1, return 1 */ + if (mp_cmp_d (a, 1) == MP_EQ) { + *c = 1; + return MP_OKAY; + } + + /* default */ + s = 0; + + /* step 3. write a = a1 * 2**k */ + if ((res = mp_init_copy (&a1, a)) != MP_OKAY) { + return res; + } + + if ((res = mp_init (&p1)) != MP_OKAY) { + goto LBL_A1; + } + + /* divide out larger power of two */ + k = mp_cnt_lsb(&a1); + if ((res = mp_div_2d(&a1, k, &a1, NULL)) != MP_OKAY) { + goto LBL_P1; + } + + /* step 4. if e is even set s=1 */ + if ((k & 1) == 0) { + s = 1; + } else { + /* else set s=1 if p = 1/7 (mod 8) or s=-1 if p = 3/5 (mod 8) */ + residue = p->dp[0] & 7; + + if (residue == 1 || residue == 7) { + s = 1; + } else if (residue == 3 || residue == 5) { + s = -1; + } + } + + /* step 5. if p == 3 (mod 4) *and* a1 == 3 (mod 4) then s = -s */ + if ( ((p->dp[0] & 3) == 3) && ((a1.dp[0] & 3) == 3)) { + s = -s; + } + + /* if a1 == 1 we're done */ + if (mp_cmp_d (&a1, 1) == MP_EQ) { + *c = s; + } else { + /* n1 = n mod a1 */ + if ((res = mp_mod (p, &a1, &p1)) != MP_OKAY) { + goto LBL_P1; + } + if ((res = mp_jacobi (&p1, &a1, &r)) != MP_OKAY) { + goto LBL_P1; + } + *c = s * r; + } + + /* done */ + res = MP_OKAY; +LBL_P1:mp_clear (&p1); +LBL_A1:mp_clear (&a1); + return res; +} +#endif + +/* $Source: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_jacobi.c,v $ */ +/* $Revision: 1.1.1.1.2.1 $ */ +/* $Date: 2005/09/26 20:16:53 $ */ |