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-rw-r--r--libtommath/bn_mp_sqrt.c25
1 files changed, 21 insertions, 4 deletions
diff --git a/libtommath/bn_mp_sqrt.c b/libtommath/bn_mp_sqrt.c
index 3aa0f38..0bba337 100644
--- a/libtommath/bn_mp_sqrt.c
+++ b/libtommath/bn_mp_sqrt.c
@@ -27,7 +27,7 @@ int mp_sqrt(mp_int *arg, mp_int *ret)
mp_int t1,t2;
int i, j, k;
#ifndef NO_FLOATING_POINT
- double d;
+ volatile double d;
mp_digit dig;
#endif
@@ -64,12 +64,29 @@ int mp_sqrt(mp_int *arg, mp_int *ret)
for (k = arg->used-1; k >= j; --k) {
d = ldexp(d, DIGIT_BIT) + (double) (arg->dp[k]);
}
+
+ /*
+ * At this point, d is the nearest floating point number to the most
+ * significant 1 or 2 mp_digits of arg. Extract its square root.
+ */
+
d = sqrt(d);
+
+ /* dig is the most significant mp_digit of the square root */
+
dig = (mp_digit) ldexp(d, -DIGIT_BIT);
+
+ /*
+ * If the most significant digit is nonzero, find the next digit down
+ * by subtracting DIGIT_BIT times thie most significant digit.
+ * Subtract one from the result so that our initial estimate is always
+ * low.
+ */
+
if (dig) {
t1.used = i+2;
d -= ldexp((double) dig, DIGIT_BIT);
- if (d != 0.0) {
+ if (d >= 1.0) {
t1.dp[i+1] = dig;
t1.dp[i] = ((mp_digit) d) - 1;
} else {
@@ -126,5 +143,5 @@ E2: mp_clear(&t1);
/* $Source: /root/tcl/repos-to-convert/tcl/libtommath/bn_mp_sqrt.c,v $ */
/* Based on Tom's 1.3 */
-/* $Revision: 1.5 $ */
-/* $Date: 2006/12/01 05:48:23 $ */
+/* $Revision: 1.6 $ */
+/* $Date: 2008/10/05 21:27:07 $ */