--- a/rust/fpnum/src/lib.rs	Sat Jul 06 00:31:54 2019 +0200
+++ b/rust/fpnum/src/lib.rs	Sat Jul 06 22:04:59 2019 +0300
@@ -70,6 +70,7 @@
         }
     }
 
+    #[inline]
     pub fn sqrt(&self) -> Self {
         debug_assert!(self.is_positive());
 
@@ -471,20 +472,18 @@
 bin_assign_op_impl!(FPPoint, ops::MulAssign<FPNum>, mul_assign, *);
 bin_assign_op_impl!(FPPoint, ops::DivAssign<FPNum>, div_assign, /);
 
-pub fn integral_sqrt(mut value: u64) -> u64 {
-    let mut digit_sqr = 0x4000_0000_0000_0000u64.wrapping_shr(value.leading_zeros() & 0xFFFF_FFFE);
-    let mut result = 0;
+pub fn integral_sqrt(value: u64) -> u64 {
+    let mut digits = (64u32 - 1).saturating_sub(value.leading_zeros()) & 0xFFFF_FFFE;
+    let mut result = if value == 0 { 0u64 } else { 1u64 };
 
-    while digit_sqr != 0 {
-        let approx = digit_sqr + result;
-        result >>= 1;
+    while digits != 0 {
+        result <<= 1;
+        if (result + 1).pow(2) <= value >> (digits - 2) {
+            result += 1;
+        }
+        digits -= 2;
+    }
 
-        if approx <= value {
-            value -= approx;
-            result += digit_sqr;
-        }
-        digit_sqr >>= 2;
-    }
     result
 }
 
@@ -506,6 +505,7 @@
     result
 }
 
+#[inline]
 pub fn distance<T>(x: T, y: T) -> FPNum
 where
     T: Into<i64> + std::fmt::Debug,