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author | Matt Johnston <matt@ucc.asn.au> | 2006-03-08 13:23:49 +0000 |
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committer | Matt Johnston <matt@ucc.asn.au> | 2006-03-08 13:23:49 +0000 |
commit | 475aa151f9618036b90a25cf529517d04e61977f (patch) | |
tree | 453ebf8873dd287a2def6a674d42afcc6637cde2 /libtommath/bn_mp_sqrt.c | |
parent | 2514a6739b3268c98ef09863eff52ed086e4b6f9 (diff) | |
parent | 2b43e46e826fe9905f36b8920386e13f1f47ed65 (diff) | |
download | dropbear-475aa151f9618036b90a25cf529517d04e61977f.tar.gz |
propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583)
to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
Diffstat (limited to 'libtommath/bn_mp_sqrt.c')
-rw-r--r-- | libtommath/bn_mp_sqrt.c | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/libtommath/bn_mp_sqrt.c b/libtommath/bn_mp_sqrt.c new file mode 100644 index 0000000..76cec87 --- /dev/null +++ b/libtommath/bn_mp_sqrt.c @@ -0,0 +1,77 @@ +#include <tommath.h> +#ifdef BN_MP_SQRT_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 + */ + +/* this function is less generic than mp_n_root, simpler and faster */ +int mp_sqrt(mp_int *arg, mp_int *ret) +{ + int res; + mp_int t1,t2; + + /* must be positive */ + if (arg->sign == MP_NEG) { + return MP_VAL; + } + + /* easy out */ + if (mp_iszero(arg) == MP_YES) { + mp_zero(ret); + return MP_OKAY; + } + + if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) { + return res; + } + + if ((res = mp_init(&t2)) != MP_OKAY) { + goto E2; + } + + /* First approx. (not very bad for large arg) */ + mp_rshd (&t1,t1.used/2); + + /* t1 > 0 */ + if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) { + goto E1; + } + if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) { + goto E1; + } + if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) { + goto E1; + } + /* And now t1 > sqrt(arg) */ + do { + if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) { + goto E1; + } + if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) { + goto E1; + } + if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) { + goto E1; + } + /* t1 >= sqrt(arg) >= t2 at this point */ + } while (mp_cmp_mag(&t1,&t2) == MP_GT); + + mp_exch(&t1,ret); + +E1: mp_clear(&t2); +E2: mp_clear(&t1); + return res; +} + +#endif |