From 1bb05560cb8e9ec667da8f587ef35cca24c161c5 Mon Sep 17 00:00:00 2001
From: Gwilym Kuiper <gw@ilym.me>
Date: Sat, 5 Jun 2021 23:50:49 +0100
Subject: [PATCH] Make it so that multiplication doesn't overflow so easily

---
 agb/src/number.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/agb/src/number.rs b/agb/src/number.rs
index 5f30e597..13fbbdf8 100644
--- a/agb/src/number.rs
+++ b/agb/src/number.rs
@@ -145,7 +145,11 @@ where
 {
     type Output = Self;
     fn mul(self, rhs: T) -> Self::Output {
-        Num((self.0 * rhs.into().0) >> N)
+        let rhs: Self = rhs.into();
+
+        Num(((self.floor() * rhs.floor()) << N)
+            + (self.floor() * rhs.frac() + rhs.floor() * self.frac())
+            + ((self.frac() * rhs.frac()) >> N))
     }
 }
 
@@ -245,6 +249,10 @@ impl<I: FixedWidthUnsignedInteger, const N: usize> Num<I, N> {
         self.0 >> N
     }
 
+    pub fn frac(&self) -> I {
+        self.0 & ((I::one() << N) - I::one())
+    }
+
     pub fn new(integral: I) -> Self {
         Self(integral << N)
     }