From 988d304c5ce1882b553503df6e8577b4856f7171 Mon Sep 17 00:00:00 2001
From: Alex <270190108+CouchRiv@users.noreply.github.com>
Date: Sun, 11 Oct 2026 11:42:42 -0400
Subject: [PATCH] fix(libc): keep the acosf result and leave errno unchanged

The previous commit replaced the out-of-range result with the default
quiet NaN 0x7fc00000, but main and FreeBSD e_acosf.c return 0xffc00000.

acosf now calls the host and restores errno, so only errno differs from
main. The guest test pins the result bits for 2.0f and -2.0f and keeps
the in-range case acosf(0.5f).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 core/libs/prx/libc/src/Math.cpp | 9 ++++-----
 core/libs/tests/GuestMath.cpp   | 8 +++-----
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/core/libs/prx/libc/src/Math.cpp b/core/libs/prx/libc/src/Math.cpp
index f6ccc2b03..f127140ab 100644
--- a/core/libs/prx/libc/src/Math.cpp
+++ b/core/libs/prx/libc/src/Math.cpp
@@ -183,11 +183,10 @@ float APS5_VABI asinf_nid_postfix(float x) {
     return result;
 }
 float APS5_VABI acosf_nid_postfix(float x) {
-    if (x < -1.0f || x > 1.0f) {
-        std::feraiseexcept(FE_INVALID);
-        return std::numeric_limits<float>::quiet_NaN();
-    }
-    return std::acos(x);
+    const int saved_errno = errno;
+    const float result = std::acos(x);
+    errno = saved_errno;
+    return result;
 }
 float APS5_VABI atan2f_nid_postfix(float y, float x) { return std::atan2(y, x); }
 float APS5_VABI hypotf_nid_postfix(float x, float y) { return static_cast<float>(std::hypot(static_cast<double>(x), static_cast<double>(y))); }
diff --git a/core/libs/tests/GuestMath.cpp b/core/libs/tests/GuestMath.cpp
index 64c693895..cc1760c60 100644
--- a/core/libs/tests/GuestMath.cpp
+++ b/core/libs/tests/GuestMath.cpp
@@ -216,13 +216,11 @@ static void CheckPowfSpecialValue() {
 
 static void CheckAcosfErrno() {
     errno = 0;
-    (void)acosf_nid_postfix(2.0f);
+    Require(std::bit_cast<std::uint32_t>(acosf_nid_postfix(2.0f)) == 0xffc00000u);
     Require(errno == 0);
-    errno = 0;
-    (void)acosf_nid_postfix(-2.0f);
+    Require(std::bit_cast<std::uint32_t>(acosf_nid_postfix(-2.0f)) == 0xffc00000u);
     Require(errno == 0);
-    errno = 0;
-    (void)acosf_nid_postfix(0.5f);
+    Require(std::bit_cast<std::uint32_t>(acosf_nid_postfix(0.5f)) == 0x3f860a92u);
     Require(errno == 0);
 }