From 721960c17244975f65f6b542e39a00d04807728e Mon Sep 17 00:00:00 2001
From: Trevor Gross <tmgross@umich.edu>
Date: Sat, 11 Jan 2025 23:40:19 +0000
Subject: [PATCH] Remove `ExpInt` from `Float`, always use `i32` instead

`ExpInt` is likely to only have performance benefits on 16-bit
platforms, but makes working with the exponent more difficult. It seems
like a worthwhile tradeoff to instead just use `i32`, so do that here.
---
 .../libm/crates/libm-test/src/f8_impl.rs      |  5 -----
 .../libm/src/math/support/float_traits.rs     | 22 +++++++------------
 .../libm/src/math/support/int_traits.rs       |  2 ++
 3 files changed, 10 insertions(+), 19 deletions(-)

diff --git a/library/compiler-builtins/libm/crates/libm-test/src/f8_impl.rs b/library/compiler-builtins/libm/crates/libm-test/src/f8_impl.rs
index d378863f2fd9..299553d202ad 100644
--- a/library/compiler-builtins/libm/crates/libm-test/src/f8_impl.rs
+++ b/library/compiler-builtins/libm/crates/libm-test/src/f8_impl.rs
@@ -20,7 +20,6 @@ pub struct f8(u8);
 impl Float for f8 {
     type Int = u8;
     type SignedInt = i8;
-    type ExpInt = i8;
 
     const ZERO: Self = Self(0b0_0000_000);
     const NEG_ZERO: Self = Self(0b1_0000_000);
@@ -62,10 +61,6 @@ impl Float for f8 {
         self.0 & Self::SIGN_MASK != 0
     }
 
-    fn exp(self) -> Self::ExpInt {
-        unimplemented!()
-    }
-
     fn from_bits(a: Self::Int) -> Self {
         Self(a)
     }
diff --git a/library/compiler-builtins/libm/src/math/support/float_traits.rs b/library/compiler-builtins/libm/src/math/support/float_traits.rs
index 697050966589..f795527db977 100644
--- a/library/compiler-builtins/libm/src/math/support/float_traits.rs
+++ b/library/compiler-builtins/libm/src/math/support/float_traits.rs
@@ -1,6 +1,6 @@
 use core::{fmt, mem, ops};
 
-use super::int_traits::{Int, MinInt};
+use super::int_traits::{CastInto, Int, MinInt};
 
 /// Trait for some basic operations on floats
 #[allow(dead_code)]
@@ -25,9 +25,6 @@ pub trait Float:
     /// A int of the same width as the float
     type SignedInt: Int + MinInt<OtherSign = Self::Int, Unsigned = Self::Int>;
 
-    /// An int capable of containing the exponent bits plus a sign bit. This is signed.
-    type ExpInt: Int;
-
     const ZERO: Self;
     const NEG_ZERO: Self;
     const ONE: Self;
@@ -98,7 +95,9 @@ pub trait Float:
     }
 
     /// Returns the exponent, not adjusting for bias.
-    fn exp(self) -> Self::ExpInt;
+    fn exp(self) -> i32 {
+        ((self.to_bits() & Self::EXP_MASK) >> Self::SIG_BITS).cast()
+    }
 
     /// Returns the significand with no implicit bit (or the "fractional" part)
     fn frac(self) -> Self::Int {
@@ -146,7 +145,6 @@ macro_rules! float_impl {
         $ty:ident,
         $ity:ident,
         $sity:ident,
-        $expty:ident,
         $bits:expr,
         $significand_bits:expr,
         $from_bits:path
@@ -154,7 +152,6 @@ macro_rules! float_impl {
         impl Float for $ty {
             type Int = $ity;
             type SignedInt = $sity;
-            type ExpInt = $expty;
 
             const ZERO: Self = 0.0;
             const NEG_ZERO: Self = -0.0;
@@ -191,9 +188,6 @@ macro_rules! float_impl {
             fn is_sign_negative(self) -> bool {
                 self.is_sign_negative()
             }
-            fn exp(self) -> Self::ExpInt {
-                ((self.to_bits() & Self::EXP_MASK) >> Self::SIG_BITS) as Self::ExpInt
-            }
             fn from_bits(a: Self::Int) -> Self {
                 Self::from_bits(a)
             }
@@ -226,11 +220,11 @@ macro_rules! float_impl {
 }
 
 #[cfg(f16_enabled)]
-float_impl!(f16, u16, i16, i8, 16, 10, f16::from_bits);
-float_impl!(f32, u32, i32, i16, 32, 23, f32_from_bits);
-float_impl!(f64, u64, i64, i16, 64, 52, f64_from_bits);
+float_impl!(f16, u16, i16, 16, 10, f16::from_bits);
+float_impl!(f32, u32, i32, 32, 23, f32_from_bits);
+float_impl!(f64, u64, i64, 64, 52, f64_from_bits);
 #[cfg(f128_enabled)]
-float_impl!(f128, u128, i128, i16, 128, 112, f128::from_bits);
+float_impl!(f128, u128, i128, 128, 112, f128::from_bits);
 
 /* FIXME(msrv): vendor some things that are not const stable at our MSRV */
 
diff --git a/library/compiler-builtins/libm/src/math/support/int_traits.rs b/library/compiler-builtins/libm/src/math/support/int_traits.rs
index 0f2d72d9be38..459f0a58bb2a 100644
--- a/library/compiler-builtins/libm/src/math/support/int_traits.rs
+++ b/library/compiler-builtins/libm/src/math/support/int_traits.rs
@@ -55,6 +55,8 @@ pub trait Int:
     + ops::BitAnd<Output = Self>
     + cmp::Ord
     + CastInto<usize>
+    + CastInto<i32>
+    + CastFrom<i32>
     + CastFrom<u8>
 {
     fn signed(self) -> OtherSign<Self::Unsigned>;