From 03255c1c53bcdb45959ef67b6f4dcfb90503d0d8 Mon Sep 17 00:00:00 2001
From: Idan Horowitz <idan.horowitz@gmail.com>
Date: Sat, 5 Jun 2021 02:53:30 +0300
Subject: [PATCH] LibJS: Handle NaN/Infinity/Zero edge cases in Math.pow()

This commit replaces the current simple call to LibM's pow with the
full implementation of 6.1.6.1.3 Number::exponentiate:
https://tc39.es/ecma262/#sec-numeric-types-number-exponentiate
---
 .../Libraries/LibJS/Runtime/MathObject.cpp    | 54 ++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/Userland/Libraries/LibJS/Runtime/MathObject.cpp b/Userland/Libraries/LibJS/Runtime/MathObject.cpp
index ac9e202175..b005d0fff6 100644
--- a/Userland/Libraries/LibJS/Runtime/MathObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/MathObject.cpp
@@ -235,7 +235,59 @@ JS_DEFINE_NATIVE_FUNCTION(MathObject::tan)
 
 JS_DEFINE_NATIVE_FUNCTION(MathObject::pow)
 {
-    return JS::exp(global_object, vm.argument(0), vm.argument(1));
+    auto base = vm.argument(0).to_number(global_object);
+    if (vm.exception())
+        return {};
+    auto exponent = vm.argument(1).to_number(global_object);
+    if (vm.exception())
+        return {};
+    if (exponent.is_nan())
+        return js_nan();
+    if (exponent.is_positive_zero() || exponent.is_negative_zero())
+        return Value(1);
+    if (base.is_nan())
+        return js_nan();
+    if (base.is_positive_infinity())
+        return exponent.as_double() > 0 ? js_infinity() : Value(0);
+    if (base.is_negative_infinity()) {
+        auto is_odd_integral_number = exponent.is_integer() && (exponent.as_i32() % 2 != 0);
+        if (exponent.as_double() > 0)
+            return is_odd_integral_number ? js_negative_infinity() : js_infinity();
+        else
+            return is_odd_integral_number ? Value(-0.0) : Value(0);
+    }
+    if (base.is_positive_zero())
+        return exponent.as_double() > 0 ? Value(0) : js_infinity();
+    if (base.is_negative_zero()) {
+        auto is_odd_integral_number = exponent.is_integer() && (exponent.as_i32() % 2 != 0);
+        if (exponent.as_double() > 0)
+            return is_odd_integral_number ? Value(-0.0) : Value(0);
+        else
+            return is_odd_integral_number ? js_negative_infinity() : js_infinity();
+    }
+    VERIFY(base.is_finite_number() && !base.is_positive_zero() && !base.is_negative_zero());
+    if (exponent.is_positive_infinity()) {
+        auto absolute_base = fabs(base.as_double());
+        if (absolute_base > 1)
+            return js_infinity();
+        else if (absolute_base == 1)
+            return js_nan();
+        else if (absolute_base < 1)
+            return Value(0);
+    }
+    if (exponent.is_negative_infinity()) {
+        auto absolute_base = fabs(base.as_double());
+        if (absolute_base > 1)
+            return Value(0);
+        else if (absolute_base == 1)
+            return js_nan();
+        else if (absolute_base < 1)
+            return js_infinity();
+    }
+    VERIFY(exponent.is_finite_number() && !exponent.is_positive_zero() && !exponent.is_negative_zero());
+    if (base.as_double() < 0 && !exponent.is_integer())
+        return js_nan();
+    return Value(::pow(base.as_double(), exponent.as_double()));
 }
 
 JS_DEFINE_NATIVE_FUNCTION(MathObject::exp)