Add functionality to BigInts which ensures a Double is returned when …

…a sqrt of a BigInt is attempted and the answer is not a BigInt.

lang_tests/int29.som

@@ -0,0 +1,18 @@
+"
+VM:
+  status: success
+  stdout:
+    Integer
+    Integer
+    Double
+    Double
+"
+
+int29 = (
+    run = (
+        (4 sqrt class) println.
+        ((1 << 200) sqrt class) println.
+        (3 sqrt class) println.
+        ((1 << 103) sqrt class) println.
+    )
+)

src/lib/vm/objects/integers.rs

@@ -16,8 +16,8 @@
 use std::convert::TryFrom;
 
 use abgc_derive::GcLayout;
-use num_bigint::BigInt;
-use num_traits::{FromPrimitive, ToPrimitive, Zero};
+use num_bigint::{BigInt, ToBigInt};
+use num_traits::{FromPrimitive, ToPrimitive};
 
 use crate::vm::{
     core::{VMError, VM},
@@ -156,10 +156,22 @@ impl Obj for ArbInt {
     }
 
     fn sqrt(&self, vm: &VM) -> Result<Val, Box<VMError>> {
-        if self.val < Zero::zero() {
-            Err(Box::new(VMError::DomainError))
+        if let Some(result) = self.val.to_f64() {
+            if result < 0.0 {
+                Err(Box::new(VMError::DomainError))
+            } else {
+                let root = result.sqrt();
+                if root.round() == root {
+                    match root.to_bigint() {
+                        Some(i) => ArbInt::new(vm, i),
+                        None => Err(Box::new(VMError::DomainError)),
+                    }
+                } else {
+                    Ok(Double::new(vm, root))
+                }
+            }
         } else {
-            ArbInt::new(vm, self.val.sqrt())
+            Err(Box::new(VMError::CantRepresentAsDouble))
         }
     }