AK: Make StringView::hash() constexpr

This required moving string_hash() to its own header so that everyone
can see it.

AK/StringHash.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2018-2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace AK {
+
+constexpr u32 string_hash(char const* characters, size_t length)
+{
+    u32 hash = 0;
+    for (size_t i = 0; i < length; ++i) {
+        hash += (u32)characters[i];
+        hash += (hash << 10);
+        hash ^= (hash >> 6);
+    }
+    hash += hash << 3;
+    hash ^= hash >> 11;
+    hash += hash << 15;
+    return hash;
+}
+
+}
+
+using AK::string_hash;

AK/StringImpl.cpp

@@ -6,9 +6,9 @@
 
 #include <AK/Debug.h>
 #include <AK/FlyString.h>
-#include <AK/HashTable.h>
 #include <AK/Memory.h>
 #include <AK/StdLibExtras.h>
+#include <AK/StringHash.h>
 #include <AK/StringImpl.h>
 #include <AK/kmalloc.h>
 

AK/StringImpl.h

@@ -96,20 +96,6 @@ private:
     char m_inline_buffer[0];
 };
 
-constexpr u32 string_hash(const char* characters, size_t length)
-{
-    u32 hash = 0;
-    for (size_t i = 0; i < length; ++i) {
-        hash += (u32)characters[i];
-        hash += (hash << 10);
-        hash ^= (hash >> 6);
-    }
-    hash += hash << 3;
-    hash ^= hash >> 11;
-    hash += hash << 15;
-    return hash;
-}
-
 template<>
 struct Formatter<StringImpl> : Formatter<StringView> {
     void format(FormatBuilder& builder, const StringImpl& value)
@@ -122,5 +108,4 @@ struct Formatter<StringImpl> : Formatter<StringView> {
 
 using AK::Chomp;
 using AK::NoChomp;
-using AK::string_hash;
 using AK::StringImpl;

AK/StringView.cpp

@@ -214,13 +214,6 @@ template Optional<u64> StringView::to_uint() const;
 template Optional<long> StringView::to_uint() const;
 template Optional<long long> StringView::to_uint() const;
 
-unsigned StringView::hash() const
-{
-    if (is_empty())
-        return 0;
-    return string_hash(characters_without_null_termination(), length());
-}
-
 bool StringView::operator==(const String& string) const
 {
     if (string.is_null())

AK/StringView.h

@@ -11,6 +11,7 @@
 #include <AK/Forward.h>
 #include <AK/Span.h>
 #include <AK/StdLibExtras.h>
+#include <AK/StringHash.h>
 #include <AK/StringUtils.h>
 #include <AK/Vector.h>
 
@@ -49,7 +50,7 @@ public:
     [[nodiscard]] constexpr bool is_null() const { return !m_characters; }
     [[nodiscard]] constexpr bool is_empty() const { return m_length == 0; }
 
-    [[nodiscard]] const char* characters_without_null_termination() const { return m_characters; }
+    [[nodiscard]] constexpr char const* characters_without_null_termination() const { return m_characters; }
     [[nodiscard]] constexpr size_t length() const { return m_length; }
 
     [[nodiscard]] ReadonlyBytes bytes() const { return { m_characters, m_length }; }
@@ -61,7 +62,12 @@ public:
     [[nodiscard]] constexpr ConstIterator begin() const { return ConstIterator::begin(*this); }
     [[nodiscard]] constexpr ConstIterator end() const { return ConstIterator::end(*this); }
 
-    [[nodiscard]] unsigned hash() const;
+    [[nodiscard]] constexpr unsigned hash() const
+    {
+        if (is_empty())
+            return 0;
+        return string_hash(characters_without_null_termination(), length());
+    }
 
     [[nodiscard]] bool starts_with(const StringView&, CaseSensitivity = CaseSensitivity::CaseSensitive) const;
     [[nodiscard]] bool ends_with(const StringView&, CaseSensitivity = CaseSensitivity::CaseSensitive) const;