From 8db5ff73e62605ad5d94bb0c17124475058b8b54 Mon Sep 17 00:00:00 2001
From: Trevor Gross <tmgross@umich.edu>
Date: Fri, 31 Jan 2025 12:31:35 +0000
Subject: [PATCH] Rename `EXP_MAX` to `EXP_SAT`

`EXP_MAX` sounds like it would be the maximum value representable by
that float type's exponent, rather than the maximum unsigned value of
its bits. Clarify this by renaming to `EXP_SAT`, the "saturated"
exponent representation.
---
 .../libm/src/math/generic/fmod.rs             |  2 +-
 .../libm/src/math/generic/sqrt.rs             |  4 ++--
 .../libm/src/math/support/float_traits.rs     | 21 +++++++++++--------
 3 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/library/compiler-builtins/libm/src/math/generic/fmod.rs b/library/compiler-builtins/libm/src/math/generic/fmod.rs
index 93da6c51e7e1..ca1cda383235 100644
--- a/library/compiler-builtins/libm/src/math/generic/fmod.rs
+++ b/library/compiler-builtins/libm/src/math/generic/fmod.rs
@@ -13,7 +13,7 @@ pub fn fmod<F: Float>(x: F, y: F) -> F {
     let mut ey = y.exp().signed();
     let sx = ix & F::SIGN_MASK;
 
-    if iy << 1 == zero || y.is_nan() || ex == F::EXP_MAX as i32 {
+    if iy << 1 == zero || y.is_nan() || ex == F::EXP_SAT as i32 {
         return (x * y) / (x * y);
     }
 
diff --git a/library/compiler-builtins/libm/src/math/generic/sqrt.rs b/library/compiler-builtins/libm/src/math/generic/sqrt.rs
index c20c0f20525e..90d6c01e9171 100644
--- a/library/compiler-builtins/libm/src/math/generic/sqrt.rs
+++ b/library/compiler-builtins/libm/src/math/generic/sqrt.rs
@@ -68,7 +68,7 @@ where
         (Exp::NoShift(()), special_case)
     } else {
         let top = u32::cast_from(ix >> F::SIG_BITS);
-        let special_case = top.wrapping_sub(1) >= F::EXP_MAX - 1;
+        let special_case = top.wrapping_sub(1) >= F::EXP_SAT - 1;
         (Exp::Shifted(top), special_case)
     };
 
@@ -119,7 +119,7 @@ where
             if even {
                 m_u2 >>= 1;
             }
-            e = (e.wrapping_add(F::EXP_MAX >> 1)) >> 1;
+            e = (e.wrapping_add(F::EXP_SAT >> 1)) >> 1;
             (m_u2, Exp::Shifted(e))
         }
         Exp::NoShift(()) => {
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 57e4aebecfc8..1fe2cb424b9a 100644
--- a/library/compiler-builtins/libm/src/math/support/float_traits.rs
+++ b/library/compiler-builtins/libm/src/math/support/float_traits.rs
@@ -48,11 +48,14 @@ pub trait Float:
     /// The bitwidth of the exponent
     const EXP_BITS: u32 = Self::BITS - Self::SIG_BITS - 1;
 
-    /// The saturated value of the exponent (infinite representation), in the rightmost postiion.
-    const EXP_MAX: u32 = (1 << Self::EXP_BITS) - 1;
+    /// The saturated (maximum bitpattern) value of the exponent, i.e. the infinite
+    /// representation.
+    ///
+    /// This shifted fully right, use `EXP_MASK` for the shifted value.
+    const EXP_SAT: u32 = (1 << Self::EXP_BITS) - 1;
 
     /// The exponent bias value
-    const EXP_BIAS: u32 = Self::EXP_MAX >> 1;
+    const EXP_BIAS: u32 = Self::EXP_SAT >> 1;
 
     /// A mask for the sign bit
     const SIGN_MASK: Self::Int;
@@ -109,7 +112,7 @@ pub trait Float:
 
     /// Returns the exponent, not adjusting for bias, not accounting for subnormals or zero.
     fn exp(self) -> u32 {
-        u32::cast_from(self.to_bits() >> Self::SIG_BITS) & Self::EXP_MAX
+        u32::cast_from(self.to_bits() >> Self::SIG_BITS) & Self::EXP_SAT
     }
 
     /// Extract the exponent and adjust it for bias, not accounting for subnormals or zero.
@@ -135,7 +138,7 @@ pub trait Float:
         let sign = if negative { Self::Int::ONE } else { Self::Int::ZERO };
         Self::from_bits(
             (sign << (Self::BITS - 1))
-                | (Self::Int::cast_from(exponent & Self::EXP_MAX) << Self::SIG_BITS)
+                | (Self::Int::cast_from(exponent & Self::EXP_SAT) << Self::SIG_BITS)
                 | (significand & Self::SIG_MASK),
         )
     }
@@ -267,7 +270,7 @@ mod tests {
     #[cfg(f16_enabled)]
     fn check_f16() {
         // Constants
-        assert_eq!(f16::EXP_MAX, 0b11111);
+        assert_eq!(f16::EXP_SAT, 0b11111);
         assert_eq!(f16::EXP_BIAS, 15);
 
         // `exp_unbiased`
@@ -289,7 +292,7 @@ mod tests {
     #[test]
     fn check_f32() {
         // Constants
-        assert_eq!(f32::EXP_MAX, 0b11111111);
+        assert_eq!(f32::EXP_SAT, 0b11111111);
         assert_eq!(f32::EXP_BIAS, 127);
 
         // `exp_unbiased`
@@ -312,7 +315,7 @@ mod tests {
     #[test]
     fn check_f64() {
         // Constants
-        assert_eq!(f64::EXP_MAX, 0b11111111111);
+        assert_eq!(f64::EXP_SAT, 0b11111111111);
         assert_eq!(f64::EXP_BIAS, 1023);
 
         // `exp_unbiased`
@@ -336,7 +339,7 @@ mod tests {
     #[cfg(f128_enabled)]
     fn check_f128() {
         // Constants
-        assert_eq!(f128::EXP_MAX, 0b111111111111111);
+        assert_eq!(f128::EXP_SAT, 0b111111111111111);
         assert_eq!(f128::EXP_BIAS, 16383);
 
         // `exp_unbiased`