AK: Implement StringView::to_{lower,upper}case_string

This patch refactors StringImpl::to_{lower,upper}case to use the new
static methods StringImpl::create_{lower,upper}cased if they have to use
to create a new StringImpl. This allows implementing StringView's
to_{lower,upper}case_string using the same methods.

It also replaces the usage of hand-written to_ascii_lowercase() and
similar methods with those from CharacterTypes.h.

AK/StringImpl.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/CharacterTypes.h>
 #include <AK/FlyString.h>
 #include <AK/HashTable.h>
 #include <AK/Memory.h>
@@ -90,60 +91,48 @@ RefPtr<StringImpl> StringImpl::create(ReadonlyBytes bytes, ShouldChomp shouldCho
     return StringImpl::create(reinterpret_cast<const char*>(bytes.data()), bytes.size(), shouldChomp);
 }
 
-static inline bool is_ascii_lowercase(char c)
+RefPtr<StringImpl> StringImpl::create_lowercased(char const* cstring, size_t length)
 {
-    return c >= 'a' && c <= 'z';
+    if (!cstring)
+        return nullptr;
+    if (!length)
+        return the_empty_stringimpl();
+    char* buffer;
+    auto impl = create_uninitialized(length, buffer);
+    for (size_t i = 0; i < length; ++i)
+        buffer[i] = (char)to_ascii_lowercase(cstring[i]);
+    return impl;
 }
 
-static inline bool is_ascii_uppercase(char c)
+RefPtr<StringImpl> StringImpl::create_uppercased(char const* cstring, size_t length)
 {
-    return c >= 'A' && c <= 'Z';
-}
-
-static inline char to_ascii_lowercase(char c)
-{
-    if (is_ascii_uppercase(c))
-        return c | 0x20;
-    return c;
-}
-
-static inline char to_ascii_uppercase(char c)
-{
-    if (is_ascii_lowercase(c))
-        return c & ~0x20;
-    return c;
+    if (!cstring)
+        return nullptr;
+    if (!length)
+        return the_empty_stringimpl();
+    char* buffer;
+    auto impl = create_uninitialized(length, buffer);
+    for (size_t i = 0; i < length; ++i)
+        buffer[i] = (char)to_ascii_uppercase(cstring[i]);
+    return impl;
 }
 
 NonnullRefPtr<StringImpl> StringImpl::to_lowercase() const
 {
     for (size_t i = 0; i < m_length; ++i) {
-        if (!is_ascii_lowercase(characters()[i]))
-            goto slow_path;
+        if (is_ascii_upper_alpha(characters()[i]))
+            return create_lowercased(characters(), m_length).release_nonnull();
     }
     return const_cast<StringImpl&>(*this);
-
-slow_path:
-    char* buffer;
-    auto lowercased = create_uninitialized(m_length, buffer);
-    for (size_t i = 0; i < m_length; ++i)
-        buffer[i] = to_ascii_lowercase(characters()[i]);
-    return lowercased;
 }
 
 NonnullRefPtr<StringImpl> StringImpl::to_uppercase() const
 {
     for (size_t i = 0; i < m_length; ++i) {
-        if (!is_ascii_uppercase(characters()[i]))
-            goto slow_path;
+        if (is_ascii_lower_alpha(characters()[i]))
+            return create_uppercased(characters(), m_length).release_nonnull();
     }
     return const_cast<StringImpl&>(*this);
-
-slow_path:
-    char* buffer;
-    auto uppercased = create_uninitialized(m_length, buffer);
-    for (size_t i = 0; i < m_length; ++i)
-        buffer[i] = to_ascii_uppercase(characters()[i]);
-    return uppercased;
 }
 
 void StringImpl::compute_hash() const

AK/StringImpl.h

@@ -26,6 +26,9 @@ public:
     static RefPtr<StringImpl> create(const char* cstring, ShouldChomp = NoChomp);
     static RefPtr<StringImpl> create(const char* cstring, size_t length, ShouldChomp = NoChomp);
     static RefPtr<StringImpl> create(ReadonlyBytes, ShouldChomp = NoChomp);
+    static RefPtr<StringImpl> create_lowercased(char const* cstring, size_t length);
+    static RefPtr<StringImpl> create_uppercased(char const* cstring, size_t length);
+
     NonnullRefPtr<StringImpl> to_lowercase() const;
     NonnullRefPtr<StringImpl> to_uppercase() const;
 

AK/StringView.cpp

@@ -173,6 +173,16 @@ bool StringView::equals_ignoring_case(const StringView& other) const
     return StringUtils::equals_ignoring_case(*this, other);
 }
 
+String StringView::to_lowercase_string() const
+{
+    return StringImpl::create_lowercased(characters_without_null_termination(), length());
+}
+
+String StringView::to_uppercase_string() const
+{
+    return StringImpl::create_uppercased(characters_without_null_termination(), length());
+}
+
 StringView StringView::substring_view_starting_from_substring(const StringView& substring) const
 {
     const char* remaining_characters = substring.characters_without_null_termination();

AK/StringView.h

@@ -83,6 +83,9 @@ public:
     [[nodiscard]] StringView trim(const StringView& characters, TrimMode mode = TrimMode::Both) const { return StringUtils::trim(*this, characters, mode); }
     [[nodiscard]] StringView trim_whitespace(TrimMode mode = TrimMode::Both) const { return StringUtils::trim_whitespace(*this, mode); }
 
+    [[nodiscard]] String to_lowercase_string() const;
+    [[nodiscard]] String to_uppercase_string() const;
+
     Optional<size_t> find_first_of(char) const;
     Optional<size_t> find_first_of(const StringView&) const;