From a9fa80ce919b7d3f71f5a18340c2e4edb943033c Mon Sep 17 00:00:00 2001
From: Juho Kahala <57393910+quaternic@users.noreply.github.com>
Date: Wed, 17 Dec 2025 07:56:45 +0200
Subject: [PATCH] Fix `expm1f` overflow threshold

Due to an erroneous overflow threshold, `expm1f` was incorrectly
returning `inf` for inputs in the range `[88.72169, 88.72283]`. This
additionally caused `sinhf` to return `NaN` for inputs in that range.

The bug was ported from the original in musl, which has since been fixed
in [1].

[1]: https://git.musl-libc.org/cgit/musl/commit/?id=964104f9f0e056cf58d9defa0b716d7756f040f6
---
 .../libm-test/src/precision.rs                | 21 -------------------
 .../compiler-builtins/libm/src/math/expm1f.rs |  4 ++--
 2 files changed, 2 insertions(+), 23 deletions(-)

diff --git a/library/compiler-builtins/libm-test/src/precision.rs b/library/compiler-builtins/libm-test/src/precision.rs
index 968ac7170c08..7887c032394b 100644
--- a/library/compiler-builtins/libm-test/src/precision.rs
+++ b/library/compiler-builtins/libm-test/src/precision.rs
@@ -218,27 +218,6 @@ impl MaybeOverride<(f16,)> for SpecialCase {}
 
 impl MaybeOverride<(f32,)> for SpecialCase {
     fn check_float<F: Float>(input: (f32,), actual: F, expected: F, ctx: &CheckCtx) -> CheckAction {
-        if ctx.base_name == BaseName::Expm1
-            && !input.0.is_infinite()
-            && input.0 > 80.0
-            && actual.is_infinite()
-            && !expected.is_infinite()
-        {
-            // we return infinity but the number is representable
-            if ctx.basis == CheckBasis::Musl {
-                return XFAIL_NOCHECK;
-            }
-            return XFAIL("expm1 representable numbers");
-        }
-
-        if ctx.base_name == BaseName::Sinh && input.0.abs() > 80.0 && actual.is_nan() {
-            // we return some NaN that should be real values or infinite
-            if ctx.basis == CheckBasis::Musl {
-                return XFAIL_NOCHECK;
-            }
-            return XFAIL("sinh unexpected NaN");
-        }
-
         if (ctx.base_name == BaseName::Lgamma || ctx.base_name == BaseName::LgammaR)
             && input.0 > 4e36
             && expected.is_infinite()
diff --git a/library/compiler-builtins/libm/src/math/expm1f.rs b/library/compiler-builtins/libm/src/math/expm1f.rs
index f77515a4b99b..388da3f30173 100644
--- a/library/compiler-builtins/libm/src/math/expm1f.rs
+++ b/library/compiler-builtins/libm/src/math/expm1f.rs
@@ -13,7 +13,6 @@
  * ====================================================
  */
 
-const O_THRESHOLD: f32 = 8.8721679688e+01; /* 0x42b17180 */
 const LN2_HI: f32 = 6.9313812256e-01; /* 0x3f317180 */
 const LN2_LO: f32 = 9.0580006145e-06; /* 0x3717f7d1 */
 const INV_LN2: f32 = 1.4426950216e+00; /* 0x3fb8aa3b */
@@ -50,7 +49,8 @@ pub fn expm1f(mut x: f32) -> f32 {
         if sign {
             return -1.;
         }
-        if x > O_THRESHOLD {
+        if hx > 0x42b17217 {
+            /* x > log(FLT_MAX) */
             x *= x1p127;
             return x;
         }