diff options
Diffstat (limited to 'libtommath/bn_mp_sqrt.c')
| -rw-r--r-- | libtommath/bn_mp_sqrt.c | 58 |
1 files changed, 50 insertions, 8 deletions
diff --git a/libtommath/bn_mp_sqrt.c b/libtommath/bn_mp_sqrt.c index ac8c2b8..72a9ff5 100644 --- a/libtommath/bn_mp_sqrt.c +++ b/libtommath/bn_mp_sqrt.c @@ -1,4 +1,5 @@ #include <tommath.h> + #ifdef BN_MP_SQRT_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * @@ -15,11 +16,20 @@ * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org */ +#ifndef NO_FLOATING_POINT +#include <math.h> +#endif + /* 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; + int i, j, k; +#ifndef NO_FLOATING_POINT + double d; + mp_digit dig; +#endif /* must be positive */ if (arg->sign == MP_NEG) { @@ -31,17 +41,49 @@ int mp_sqrt(mp_int *arg, mp_int *ret) mp_zero(ret); return MP_OKAY; } - - if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) { - return res; + + i = (arg->used / 2) - 1; + j = 2 * i; + if ((res = mp_init_size(&t1, i+2)) != 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); + for (k = 0; k < i; ++k) { + t1.dp[k] = (mp_digit) 0; + } + +#ifndef NO_FLOATING_POINT + + /* Estimate the square root using the hardware floating point unit. */ + + d = 0.0; + for (k = arg->used-1; k >= j; --k) { + d = ldexp(d, DIGIT_BIT) + (double) (arg->dp[k]); + } + d = sqrt(d); + dig = (mp_digit) ldexp(d, -DIGIT_BIT); + if (dig) { + t1.used = i+2; + t1.dp[i+1] = dig; + d -= ldexp((double) dig, DIGIT_BIT); + } else { + t1.used = i+1; + } + t1.dp[i] = (mp_digit) d; + +#else + + /* Estimate the square root as having 1 in the most significant place. */ + + t1.used = i + 2; + t1.dp[i+1] = (mp_digit) 1; + t1.dp[i] = (mp_digit) 0; + +#endif /* t1 > 0 */ if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) { @@ -77,5 +119,5 @@ E2: mp_clear(&t1); #endif /* $Source: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_sqrt.c,v $ */ -/* $Revision: 1.1.1.2 $ */ -/* $Date: 2005/09/26 16:31:56 $ */ +/* $Revision: 1.2 $ */ +/* $Date: 2005/12/27 17:39:02 $ */ |