move ensure module and ArithmeticError to sp-arithmetic

primitives/arithmetic/src/lib.rs

@@ -50,6 +50,34 @@ pub use rational::{Rational128, RationalInfinite};
 use sp_std::{cmp::Ordering, fmt::Debug, prelude::*};
 use traits::{BaseArithmetic, One, SaturatedConversion, Unsigned, Zero};
 
+use codec::{Decode, Encode};
+use scale_info::TypeInfo;
+
+#[cfg(feature = "std")]
+use serde::{Deserialize, Serialize};
+
+/// Arithmetic errors.
+#[derive(Eq, PartialEq, Clone, Copy, Encode, Decode, Debug, TypeInfo)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub enum ArithmeticError {
+	/// Underflow.
+	Underflow,
+	/// Overflow.
+	Overflow,
+	/// Division by zero.
+	DivisionByZero,
+}
+
+impl From<ArithmeticError> for &'static str {
+	fn from(e: ArithmeticError) -> &'static str {
+		match e {
+			ArithmeticError::Underflow => "An underflow would occur",
+			ArithmeticError::Overflow => "An overflow would occur",
+			ArithmeticError::DivisionByZero => "Division by zero",
+		}
+	}
+}
+
 /// Trait for comparing two numbers with an threshold.
 ///
 /// Returns: