Merge pull request #43 from gwilymk/add-rem-and-rem-euclid

Add rem and rem euclid implementations for fixnum

agb/src/number.rs

@@ -1,9 +1,9 @@
 use core::{
-    fmt::Display,
-    ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Neg, Sub, SubAssign},
+    fmt::{Debug, Display},
+    ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Neg, Rem, RemAssign, Sub, SubAssign},
 };
 
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Num<const N: usize>(i32);
 
 pub fn change_base<const N: usize, const M: usize>(num: Num<N>) -> Num<M> {
@@ -96,6 +96,25 @@ where
     }
 }
 
+impl<T, const N: usize> Rem<T> for Num<N>
+where
+    T: Into<Num<N>>,
+{
+    type Output = Self;
+    fn rem(self, modulus: T) -> Self::Output {
+        Num(self.0 % modulus.into().0)
+    }
+}
+
+impl<T, const N: usize> RemAssign<T> for Num<N>
+where
+    T: Into<Num<N>>,
+{
+    fn rem_assign(&mut self, modulus: T) {
+        self.0 = (*self % modulus).0
+    }
+}
+
 impl<const N: usize> Neg for Num<N> {
     type Output = Self;
     fn neg(self) -> Self::Output {
@@ -107,12 +126,33 @@ impl<const N: usize> Num<N> {
     pub fn max() -> Self {
         Num(i32::MAX)
     }
+
     pub fn min() -> Self {
         Num(i32::MIN)
     }
 
     pub fn int(&self) -> i32 {
-        self.0 >> N
+        let fractional_part = self.0 & ((1 << N) - 1);
+        let self_as_int = self.0 >> N;
+
+        if self_as_int < 0 && fractional_part != 0 {
+            self_as_int + 1
+        } else {
+            self_as_int
+        }
+    }
+
+    pub fn rem_euclid(&self, rhs: Self) -> Self {
+        let r = *self % rhs;
+        if r < 0.into() {
+            if rhs < 0.into() {
+                r - rhs
+            } else {
+                r + rhs
+            }
+        } else {
+            r
+        }
     }
 
     pub fn new(integral: i32) -> Self {
@@ -183,6 +223,71 @@ fn test_change_base(_gba: &mut super::Gba) {
     assert_eq!(three + change_base(two), 5.into());
 }
 
+#[test_case]
+fn test_rem_returns_sensible_values_for_integers(_gba: &mut super::Gba) {
+    for i in -50..50 {
+        for j in -50..50 {
+            if j == 0 {
+                continue;
+            }
+
+            let i_rem_j_normally = i % j;
+            let i_fixnum: Num<8> = i.into();
+
+            assert_eq!(i_fixnum % j, i_rem_j_normally.into());
+        }
+    }
+}
+
+#[test_case]
+fn test_rem_returns_sensible_values_for_non_integers(_gba: &mut super::Gba) {
+    let one: Num<8> = 1.into();
+    let third = one / 3;
+
+    for i in -50..50 {
+        for j in -50..50 {
+            if j == 0 {
+                continue;
+            }
+
+            // full calculation in the normal way
+            let x: Num<8> = third + i;
+            let y: Num<8> = j.into();
+
+            let truncated_division: Num<8> = (x / y).int().into();
+
+            let remainder = x - truncated_division * y;
+
+            assert_eq!(x % y, remainder);
+        }
+    }
+}
+
+#[test_case]
+fn test_rem_euclid_is_always_positive_and_sensible(_gba: &mut super::Gba) {
+    let one: Num<8> = 1.into();
+    let third = one / 3;
+
+    for i in -50..50 {
+        for j in -50..50 {
+            if j == 0 {
+                continue;
+            }
+
+            // full calculation in the normal way
+            let x: Num<8> = third + i;
+            let y: Num<8> = j.into();
+
+            let truncated_division: Num<8> = (x / y).int().into();
+
+            let remainder = x - truncated_division * y;
+
+            let rem_euclid = x.rem_euclid(y);
+            assert!(rem_euclid > 0.into());
+        }
+    }
+}
+
 impl<const N: usize> Display for Num<N> {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         let integral = self.0 >> N;
@@ -203,3 +308,9 @@ impl<const N: usize> Display for Num<N> {
         Ok(())
     }
 }
+
+impl<const N: usize> Debug for Num<N> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "Num<{}>({})", N, self)
+    }
+}