From 8a94b69d85866240ff17997964913090747b5ecf Mon Sep 17 00:00:00 2001
From: Amanieu d'Antras <amanieu@gmail.com>
Date: Thu, 11 Aug 2016 05:28:15 +0100
Subject: [PATCH] Add traits for integer operations

---
 src/lib.rs | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 59 insertions(+), 4 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 01aca76..3ef1354 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -9,21 +9,76 @@
 #[cfg(test)]
 extern crate core;
 
-use core::mem;
-
 #[cfg(target_arch = "arm")]
 pub mod arm;
 
 #[cfg(test)]
 mod test;
 
-const CHAR_BITS: usize = 8;
+/// Trait for some basic operations on integers
+trait Int {
+    fn bits() -> usize;
+}
+
+// TODO: Once i128/u128 support lands, we'll want to add impls for those as well
+impl Int for u32 {
+    fn bits() -> usize { 32 }
+}
+impl Int for i32 {
+    fn bits() -> usize { 32 }
+}
+impl Int for u64 {
+    fn bits() -> usize { 64 }
+}
+impl Int for i64 {
+    fn bits() -> usize { 64 }
+}
+
+/// Trait to convert an integer to/from smaller parts
+trait LargeInt {
+    type LowHalf;
+    type HighHalf;
+
+    fn low(self) -> Self::LowHalf;
+    fn high(self) -> Self::HighHalf;
+    fn from_parts(low: Self::LowHalf, high: Self::HighHalf) -> Self;
+}
+
+// TODO: Once i128/u128 support lands, we'll want to add impls for those as well
+impl LargeInt for u64 {
+    type LowHalf = u32;
+    type HighHalf = u32;
+
+    fn low(self) -> u32 {
+        self as u32
+    }
+    fn high(self) -> u32 {
+        (self >> 32) as u32
+    }
+    fn from_parts(low: u32, high: u32) -> u64 {
+        low as u64 | ((high as u64) << 32)
+    }
+}
+impl LargeInt for i64 {
+    type LowHalf = u32;
+    type HighHalf = i32;
+
+    fn low(self) -> u32 {
+        self as u32
+    }
+    fn high(self) -> i32 {
+        (self >> 32) as i32
+    }
+    fn from_parts(low: u32, high: i32) -> i64 {
+        low as i64 | ((high as i64) << 32)
+    }
+}
 
 macro_rules! absv_i2 {
     ($intrinsic:ident : $ty:ty) => {
         #[no_mangle]
         pub extern "C" fn $intrinsic(x: $ty) -> $ty {
-            let n = mem::size_of::<$ty>() * CHAR_BITS;
+            let n = <$ty>::bits();
             if x == 1 << (n - 1) {
                 panic!();
             }