fixed rounding rescaling

math/src/num_bigint.rs

@@ -0,0 +1,34 @@
+use num_bigint::BigInt;
+use num_bigint::Sign;
+use num_integer::Integer;
+use num_traits::{Zero, One, Signed};
+
+pub trait Div{
+    fn div_floor(&self, other: &Self) -> Self;
+    fn div_round(&self, other: &Self) -> Self;
+}
+
+impl Div for BigInt{
+
+    fn div_floor(&self, other:&Self) -> Self{
+        let quo: BigInt = self / other;
+        if self.sign() == Sign::Minus {
+            return quo - BigInt::one()
+        }
+        return quo
+    }
+
+    fn div_round(&self, other:&Self) -> Self{
+        let (quo, mut rem) = self.div_rem(other);
+        rem <<= 1;
+        if rem != BigInt::zero() && &rem.abs() > other{
+            if self.sign() == other.sign(){
+                return quo + BigInt::one()
+            }else{
+                return quo - BigInt::one()
+            }
+        }
+        return quo
+    }
+}
+