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-rw-r--r--libtommath/bn_mp_sqrt.c58
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 $ */