1 files changed, 142 insertions, 0 deletions
diff --git a/libtommath/bn_mp_sqrt.c b/libtommath/bn_mp_sqrt.c
new file mode 100644
index 0000000..016b8ba
--- /dev/null
+++ b/libtommath/bn_mp_sqrt.c
@@ -0,0 +1,142 @@
+#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@gmail.com, http://math.libtomcrypt.com
+ */
+
+#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
+  volatile double d;
+  mp_digit dig;
+#endif
+
+  /* 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;
+  }
+  
+  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;
+  }
+
+  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]);
+  }
+
+  /* 
+   * 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 >= 1.0) {
+	  t1.dp[i+1] = dig;
+	  t1.dp[i] = ((mp_digit) d) - 1;
+      } else {
+	  t1.dp[i+1] = dig-1;
+	  t1.dp[i] = MP_DIGIT_MAX;
+      }
+  } else {
+      t1.used = i+1;
+      t1.dp[i] = ((mp_digit) d) - 1;
+  }
+
+#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) {
+    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