Complete 'Round' trait implementation of 'Fraction' generic struct

lycantropos · Jun 20, 2023 · 1578e0b · 1578e0b
1 parent e99e95c
commit 1578e0b
Showing 1 changed file with 75 additions and 17 deletions.
diff --git a/src/fraction/round.rs b/src/fraction/round.rs
@@ -9,20 +9,20 @@ use crate::big_int::BigInt;
 
 use super::types::Fraction;
 
-impl<Digit, const DIGIT_BITNESS: usize> Round
-    for Fraction<BigInt<Digit, DIGIT_BITNESS>>
+impl<'a, Digit, const DIGIT_BITNESS: usize> Round
+    for &'a Fraction<BigInt<Digit, DIGIT_BITNESS>>
 where
-    for<'a> &'a BigInt<Digit, DIGIT_BITNESS>: Parity + Signed,
-    for<'a> BigInt<Digit, DIGIT_BITNESS>: Add<Output = BigInt<Digit, DIGIT_BITNESS>>
-        + CheckedDivRemEuclid<
-            &'a BigInt<Digit, DIGIT_BITNESS>,
-            Output = Option<(
-                BigInt<Digit, DIGIT_BITNESS>,
-                BigInt<Digit, DIGIT_BITNESS>,
-            )>,
-        > + One
+    &'a BigInt<Digit, DIGIT_BITNESS>: CheckedDivRemEuclid<
+        Output = Option<(
+            BigInt<Digit, DIGIT_BITNESS>,
+            BigInt<Digit, DIGIT_BITNESS>,
+        )>,
+    >,
+    BigInt<Digit, DIGIT_BITNESS>: Add<Output = BigInt<Digit, DIGIT_BITNESS>>
+        + One
         + Ord
         + Shl<usize, Output = BigInt<Digit, DIGIT_BITNESS>>,
+    for<'b> &'b BigInt<Digit, DIGIT_BITNESS>: Parity + Signed,
 {
     type Output = BigInt<Digit, DIGIT_BITNESS>;
 
@@ -54,17 +54,17 @@ where
 }
 
 impl<Digit, const DIGIT_BITNESS: usize> Round
-    for &Fraction<BigInt<Digit, DIGIT_BITNESS>>
+    for Fraction<BigInt<Digit, DIGIT_BITNESS>>
 where
-    for<'a> &'a BigInt<Digit, DIGIT_BITNESS>: CheckedDivRemEuclid<
+    for<'a> &'a BigInt<Digit, DIGIT_BITNESS>: Parity + Signed,
+    for<'a> BigInt<Digit, DIGIT_BITNESS>: Add<Output = BigInt<Digit, DIGIT_BITNESS>>
+        + CheckedDivRemEuclid<
+            &'a BigInt<Digit, DIGIT_BITNESS>,
             Output = Option<(
                 BigInt<Digit, DIGIT_BITNESS>,
                 BigInt<Digit, DIGIT_BITNESS>,
             )>,
-        > + Parity
-        + Signed,
-    for<'a> BigInt<Digit, DIGIT_BITNESS>: Add<Output = BigInt<Digit, DIGIT_BITNESS>>
-        + One
+        > + One
         + Ord
         + Shl<usize, Output = BigInt<Digit, DIGIT_BITNESS>>,
 {
@@ -99,6 +99,36 @@ where
 
 macro_rules! signed_integer_fraction_round_impl {
     ($($integer:ty)*) => ($(
+        impl Round for &Fraction<$integer> {
+            type Output = $integer;
+
+            fn round(self, tie_breaking: TieBreaking) -> Self::Output {
+                let (quotient, remainder) = unsafe {
+                    self.numerator
+                        .checked_div_rem_euclid(self.denominator)
+                        .unwrap_unchecked()
+                };
+                match (remainder << 1).cmp(&self.denominator) {
+                    Ordering::Equal => {
+                        if match tie_breaking {
+                            TieBreaking::AwayFromZero => {
+                                !quotient.is_negative()
+                            }
+                            TieBreaking::ToEven => quotient.is_odd(),
+                            TieBreaking::ToOdd => quotient.is_even(),
+                            TieBreaking::TowardZero => quotient.is_negative(),
+                        } {
+                            quotient + 1
+                        } else {
+                            quotient
+                        }
+                    }
+                    Ordering::Greater => quotient + 1,
+                    Ordering::Less => quotient,
+                }
+            }
+        }
+
         impl Round for Fraction<$integer> {
             type Output = $integer;
 
@@ -135,6 +165,34 @@ signed_integer_fraction_round_impl!(i8 i16 i32 i64 i128 isize);
 
 macro_rules! unsigned_integer_fraction_round_impl {
     ($($integer:ty)*) => ($(
+        impl Round for &Fraction<$integer> {
+            type Output = $integer;
+
+            fn round(self, tie_breaking: TieBreaking) -> Self::Output {
+                let (quotient, remainder) = unsafe {
+                    self.numerator
+                        .checked_div_rem_euclid(self.denominator)
+                        .unwrap_unchecked()
+                };
+                match (remainder << 1).cmp(&self.denominator) {
+                    Ordering::Equal => {
+                        if match tie_breaking {
+                            TieBreaking::AwayFromZero => true,
+                            TieBreaking::ToEven => quotient.is_odd(),
+                            TieBreaking::ToOdd => quotient.is_even(),
+                            TieBreaking::TowardZero => false,
+                        } {
+                            quotient + 1
+                        } else {
+                            quotient
+                        }
+                    }
+                    Ordering::Greater => quotient + 1,
+                    Ordering::Less => quotient,
+                }
+            }
+        }
+
         impl Round for Fraction<$integer> {
             type Output = $integer;