From 5883c255521226bba9a059d08ea2fdb705d012a1 Mon Sep 17 00:00:00 2001
From: ivica00 <ivica00@users.noreply.github.com>
Date: Mon, 12 Oct 2026 22:51:11 +0200
Subject: [PATCH] feat(libc): implement nearbyint

The float helper is already on main. The double helper rounds with the current mode and does not raise the inexact flag.
---
 core/libs/prx/libc/src/Math.cpp |  1 +
 core/libs/tests/GuestMath.cpp   | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/core/libs/prx/libc/src/Math.cpp b/core/libs/prx/libc/src/Math.cpp
index 031ac5c4e..154bfa5ae 100644
--- a/core/libs/prx/libc/src/Math.cpp
+++ b/core/libs/prx/libc/src/Math.cpp
@@ -183,6 +183,7 @@ int APS5_VABI __isnormalf_nid_postfix(float x) { return std::isnormal(x) ? 1 : 0
 int APS5_VABI __isinff_nid_postfix(float x) { return std::isinf(x) ? 1 : 0; }
 float APS5_VABI nearbyintf_nid_postfix(float x) { return std::nearbyintf(x); }
 long double APS5_VABI nearbyintl_nid_postfix(long double x) { return std::nearbyint(x); }
+double APS5_VABI nearbyint_nid_postfix(double x) { return std::nearbyint(x); }
 
 double APS5_VABI cbrt_nid_postfix(double x) { return std::cbrt(x); }
 double APS5_VABI asin_nid_postfix(double x) {
diff --git a/core/libs/tests/GuestMath.cpp b/core/libs/tests/GuestMath.cpp
index 68ddcf1ec..103c6e5bd 100644
--- a/core/libs/tests/GuestMath.cpp
+++ b/core/libs/tests/GuestMath.cpp
@@ -34,6 +34,7 @@ double APS5_VABI fabs_nid_postfix(double);
 int APS5_VABI abs_nid_postfix(int);
 double APS5_VABI trunc_nid_postfix(double);
 double APS5_VABI ceil_nid_postfix(double);
+double APS5_VABI nearbyint_nid_postfix(double);
 double APS5_VABI fma_nid_postfix(double, double, double);
 long double APS5_VABI acosl_nid_postfix(long double);
 long double APS5_VABI asinl_nid_postfix(long double);
@@ -152,6 +153,19 @@ static void CheckExactOperations() {
     Require(std::isnan(fma_nid_postfix(INFINITY, 0., 1.)));
 }
 
+static void CheckNearbyint() {
+    std::feclearexcept(FE_ALL_EXCEPT);
+    const double zero = nearbyint_nid_postfix(0.5);
+    Require(zero == 0.0 && !std::signbit(zero));
+    Require(nearbyint_nid_postfix(1.5) == 2.0 && nearbyint_nid_postfix(2.5) == 2.0);
+    Require(nearbyint_nid_postfix(2.7) == 3.0 && nearbyint_nid_postfix(-2.7) == -3.0);
+    Require(std::bit_cast<std::uint64_t>(nearbyint_nid_postfix(-0.5)) == 0x8000000000000000ull);
+    Require(nearbyint_nid_postfix(0x1p53) == 0x1p53);
+    Require(nearbyint_nid_postfix(INFINITY) == INFINITY && nearbyint_nid_postfix(-INFINITY) == -INFINITY);
+    Require(std::isnan(nearbyint_nid_postfix(NAN)));
+    Require(std::fetestexcept(FE_INEXACT) == 0);
+}
+
 static bool ExtendedBits(long double value, std::uint64_t mantissa, std::uint16_t signExponent) {
     unsigned char bytes[sizeof(long double)]{};
     std::memcpy(bytes, &value, sizeof(value));
@@ -709,6 +723,7 @@ int main() {
     CheckSquareRoot();
     CheckExp2Errno();
     CheckExactOperations();
+    CheckNearbyint();
     CheckLongDouble();
     CheckNearbyintl();
     CheckAsinl();