AK: Implement ShortString for big-endian

AK/StringBase.h

@@ -14,26 +14,29 @@ namespace AK::Detail {
 
 class StringData;
 
-static constexpr size_t MAX_SHORT_STRING_BYTE_COUNT = sizeof(StringData*) - 1;
+static constexpr size_t MAX_SHORT_STRING_BYTE_COUNT = sizeof(StringData*) - sizeof(u8);
 
 struct ShortString {
     ReadonlyBytes bytes() const;
     size_t byte_count() const;
 
     // NOTE: This is the byte count shifted left 1 step and or'ed with a 1 (the SHORT_STRING_FLAG)
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     u8 byte_count_and_short_string_flag { 0 };
     u8 storage[MAX_SHORT_STRING_BYTE_COUNT] = { 0 };
+#else
+    u8 storage[MAX_SHORT_STRING_BYTE_COUNT] = { 0 };
+    u8 byte_count_and_short_string_flag { 0 };
+#endif
 };
 
-static_assert(HostIsLittleEndian, "Order of fields in ShortString assumes LE.");
-static_assert(sizeof(ShortString) >= sizeof(StringData*));
-static_assert(__builtin_offsetof(ShortString, byte_count_and_short_string_flag) == 0);
+static_assert(sizeof(ShortString) == sizeof(StringData*));
 
 class StringBase {
 public:
     // Creates an empty (zero-length) String.
     constexpr StringBase()
-        : StringBase(ShortString { SHORT_STRING_FLAG, {} })
+        : StringBase(ShortString { .byte_count_and_short_string_flag = SHORT_STRING_FLAG })
     {
     }
 

Tests/AK/TestString.cpp

@@ -63,27 +63,37 @@ TEST_CASE(copy_assignment)
 
 TEST_CASE(short_strings)
 {
+    /** NOTE: make sure that the test strings' first character has an even ASCII code.
+     *        This is important for the odd pointer address checks (this is to
+     *        test if the ShortString structs are endian agnostic). */
 #ifdef AK_ARCH_64_BIT
-    auto string1 = MUST(String::from_utf8("abcdefg"sv));
+    auto string1 = MUST(String::from_utf8("foo bar"sv));
     EXPECT_EQ(string1.is_short_string(), true);
     EXPECT_EQ(string1.bytes().size(), 7u);
-    EXPECT_EQ(string1.bytes_as_string_view(), "abcdefg"sv);
+    EXPECT_EQ(string1.bytes_as_string_view(), "foo bar"sv);
+    // check for odd "pointer" value, i.e. short string flag
+    EXPECT_EQ(*((uintptr_t*)&string1) % 2UL, 1U);
 
-    auto string2 = "abcdefg"_string;
+    auto string2 = "foo bar"_string;
     EXPECT_EQ(string2.is_short_string(), true);
     EXPECT_EQ(string2.bytes().size(), 7u);
     EXPECT_EQ(string2, string1);
-
+    // check for odd "pointer" value, i.e. short string flag
+    EXPECT_EQ(*((uintptr_t*)&string2) % 2UL, 1U);
 #else
-    auto string1 = MUST(String::from_utf8("abc"sv));
+    auto string1 = MUST(String::from_utf8("foo"sv));
     EXPECT_EQ(string1.is_short_string(), true);
     EXPECT_EQ(string1.bytes().size(), 3u);
-    EXPECT_EQ(string1.bytes_as_string_view(), "abc"sv);
+    EXPECT_EQ(string1.bytes_as_string_view(), "foo"sv);
+    // check for odd "pointer" value, i.e. short string flag
+    EXPECT_EQ(*((uintptr_t*)&string1) % 2U, 1U);
 
-    auto string2 = "abc"_string;
+    auto string2 = "foo"_string;
     EXPECT_EQ(string2.is_short_string(), true);
     EXPECT_EQ(string2.bytes().size(), 3u);
     EXPECT_EQ(string2, string1);
+    // check for odd "pointer" value, i.e. short string flag
+    EXPECT_EQ(*((uintptr_t*)&string2) % 2U, 1U);
 #endif
 }