From 94f5389934aeb2060fb3d85f34269138424d834d Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Mon, 12 Jun 2023 13:28:25 +0330
Subject: [PATCH] AK: Add a 'HostIsLittleEndian' constant and use it instead of
 BYTE_ORDER

Previously we were using the preprocessor everywhere we needed this
constant, so let's move away from that and use a constexpr constant.
---
 AK/Endian.h                                   | 45 ++++++++++---------
 AK/FloatingPointStringConversions.cpp         |  6 +--
 .../Libraries/LibJS/Runtime/AtomicsObject.cpp |  2 +-
 3 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/AK/Endian.h b/AK/Endian.h
index 05743cb119..e3636e6758 100644
--- a/AK/Endian.h
+++ b/AK/Endian.h
@@ -35,39 +35,40 @@
 #endif
 
 namespace AK {
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+inline constexpr static bool HostIsLittleEndian = true;
+#else
+inline constexpr static bool HostIsLittleEndian = false;
+#endif
 
 template<typename T>
 ALWAYS_INLINE constexpr T convert_between_host_and_little_endian(T value)
 {
-#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-    return value;
-#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
-    if constexpr (sizeof(T) == 8)
-        return static_cast<T>(__builtin_bswap64(static_cast<u64>(value)));
-    if constexpr (sizeof(T) == 4)
-        return static_cast<T>(__builtin_bswap32(static_cast<u32>(value)));
-    if constexpr (sizeof(T) == 2)
-        return static_cast<T>(__builtin_bswap16(static_cast<u16>(value)));
-    if constexpr (sizeof(T) == 1)
+    if constexpr (HostIsLittleEndian || sizeof(T) == 1)
         return value;
-#endif
+    else if constexpr (sizeof(T) == 8)
+        return static_cast<T>(__builtin_bswap64(static_cast<u64>(value)));
+    else if constexpr (sizeof(T) == 4)
+        return static_cast<T>(__builtin_bswap32(static_cast<u32>(value)));
+    else if constexpr (sizeof(T) == 2)
+        return static_cast<T>(__builtin_bswap16(static_cast<u16>(value)));
+    else
+        static_assert(DependentFalse<T>, "Cannot byte-swap values larger than 64-bits");
 }
 
 template<typename T>
 ALWAYS_INLINE constexpr T convert_between_host_and_big_endian(T value)
 {
-#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-    if constexpr (sizeof(T) == 8)
-        return static_cast<T>(__builtin_bswap64(static_cast<u64>(value)));
-    if constexpr (sizeof(T) == 4)
-        return static_cast<T>(__builtin_bswap32(static_cast<u32>(value)));
-    if constexpr (sizeof(T) == 2)
-        return static_cast<T>(__builtin_bswap16(static_cast<u16>(value)));
-    if constexpr (sizeof(T) == 1)
+    if constexpr (sizeof(T) == 1 || !HostIsLittleEndian)
         return value;
-#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
-    return value;
-#endif
+    else if constexpr (sizeof(T) == 8)
+        return static_cast<T>(__builtin_bswap64(static_cast<u64>(value)));
+    else if constexpr (sizeof(T) == 4)
+        return static_cast<T>(__builtin_bswap32(static_cast<u32>(value)));
+    else if constexpr (sizeof(T) == 2)
+        return static_cast<T>(__builtin_bswap16(static_cast<u16>(value)));
+    else
+        static_assert(DependentFalse<T>, "Cannot byte-swap values larger than 64-bits");
 }
 
 template<typename T>
diff --git a/AK/FloatingPointStringConversions.cpp b/AK/FloatingPointStringConversions.cpp
index 8a26dc2c28..d63aaa5231 100644
--- a/AK/FloatingPointStringConversions.cpp
+++ b/AK/FloatingPointStringConversions.cpp
@@ -176,10 +176,8 @@ static constexpr auto max_representable_power_of_ten_in_u64 = 19;
 static_assert(1e19 <= static_cast<double>(NumericLimits<u64>::max()));
 static_assert(1e20 >= static_cast<double>(NumericLimits<u64>::max()));
 
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
-#    error Float parsing currently assumes little endian, this fact is only used in fast parsing of 8 digits at a time \
-           you _should_ only need to change read eight_digits to make this big endian compatible.
-#endif
+static_assert(HostIsLittleEndian, "Float parsing currently assumes little endian, this fact is only used in fast parsing of 8 digits at a time"
+                                  "\nyou _should_ only need to change read eight_digits to make this big endian compatible.");
 constexpr u64 read_eight_digits(char const* string)
 {
     u64 val;
diff --git a/Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp b/Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp
index 423beec7e9..a93ce76580 100644
--- a/Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp
@@ -225,7 +225,7 @@ static ThrowCompletionOr<Value> atomic_compare_exchange_impl(VM& vm, TypedArrayB
     // 9. Let elementSize be TypedArrayElementSize(typedArray).
 
     // 10. Let isLittleEndian be the value of the [[LittleEndian]] field of the surrounding agent's Agent Record.
-    constexpr bool is_little_endian = __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__;
+    constexpr bool is_little_endian = AK::HostIsLittleEndian;
 
     // 11. Let expectedBytes be NumericToRawBytes(elementType, expected, isLittleEndian).
     auto expected_bytes = MUST_OR_THROW_OOM(numeric_to_raw_bytes<T>(vm, expected, is_little_endian));