Bug 1358297: Part 2. Helper class to mask ascii characters, letting us do a faster test for membership in a string/character set. r=froydnj

MozReview-Commit-ID: 1s3mYNVThoD

--HG--
extra : rebase_source : d9c845addaa4a7a326b787a99f5cc83abb567848

xpcom/string/moz.build

@@ -8,6 +8,7 @@ with Files('**'):
     BUG_COMPONENT = ('Core', 'String')
 
 EXPORTS += [
+    'nsASCIIMask.h',
     'nsAString.h',
     'nsCharTraits.h',
     'nsDependentString.h',
@@ -38,6 +39,7 @@ EXPORTS += [
 ]
 
 UNIFIED_SOURCES += [
+    'nsASCIIMask.cpp',
     'nsDependentString.cpp',
     'nsDependentSubstring.cpp',
     'nsPromiseFlatString.cpp',

xpcom/string/nsASCIIMask.cpp

@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsASCIIMask.h"
+
+namespace mozilla {
+
+constexpr bool TestWhitespace(char c)
+{
+  return c == '\f' || c == '\t' || c == '\r' || c == '\n' || c == ' ';
+}
+constexpr ASCIIMaskArray sWhitespaceMask = CreateASCIIMask(TestWhitespace);
+
+constexpr bool TestCRLF(char c)
+{
+  return c == '\r' || c == '\n';
+}
+constexpr ASCIIMaskArray sCRLFMask = CreateASCIIMask(TestCRLF);
+
+constexpr bool TestCRLFTab(char c)
+{
+  return c == '\r' || c == '\n' || c == '\t';
+}
+constexpr ASCIIMaskArray sCRLFTabMask = CreateASCIIMask(TestCRLFTab);
+
+constexpr bool TestZeroToNine(char c)
+{
+  return c == '0' || c == '1' || c == '2' || c == '3' || c == '4' ||
+         c == '5' || c == '6' || c == '7' || c == '8' || c == '9';
+}
+constexpr ASCIIMaskArray sZeroToNineMask = CreateASCIIMask(TestZeroToNine);
+
+const ASCIIMaskArray& ASCIIMask::MaskWhitespace()
+{
+  return sWhitespaceMask;
+}
+
+const ASCIIMaskArray& ASCIIMask::MaskCRLF()
+{
+  return sCRLFMask;
+}
+
+const ASCIIMaskArray& ASCIIMask::MaskCRLFTab()
+{
+  return sCRLFTabMask;
+}
+
+const ASCIIMaskArray& ASCIIMask::Mask0to9()
+{
+  return sZeroToNineMask;
+}
+
+} // namespace mozilla

xpcom/string/nsASCIIMask.h

@@ -0,0 +1,70 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsASCIIMask_h_
+#define nsASCIIMask_h_
+
+#include <array>
+#include "mozilla/IndexSequence.h"
+
+typedef std::array<bool, 128> ASCIIMaskArray;
+
+namespace mozilla {
+
+// Boolean arrays, fixed size and filled in at compile time, meant to
+// record something about each of the (standard) ASCII characters.
+// No extended ASCII for now, there has been no use case.
+// If you have loops that go through a string character by character
+// and test for equality to a certain set of characters before deciding
+// on a course of action, chances are building up one of these arrays
+// and using it is going to be faster, especially if the set of
+// characters is more than one long, and known at compile time.
+class ASCIIMask
+{
+public:
+  // Preset masks for some common character groups
+  // When testing, you must check if the index is < 128 or use IsMasked()
+  //
+  // if (someChar < 128 && MaskCRLF()[someChar]) this is \r or \n
+
+  static const ASCIIMaskArray& MaskCRLF();
+  static const ASCIIMaskArray& Mask0to9();
+  static const ASCIIMaskArray& MaskCRLFTab();
+  static const ASCIIMaskArray& MaskWhitespace();
+
+  static MOZ_ALWAYS_INLINE bool IsMasked(const ASCIIMaskArray& aMask, uint32_t aChar)
+  {
+    return aChar < 128 && aMask[aChar];
+  }
+};
+
+// Outside of the preset ones, use these templates to create more masks.
+//
+// The example creation will look like this:
+//
+// constexpr bool TestABC(char c) { return c == 'A' || c == 'B' || c == 'C'; }
+// constexpr std::array<bool, 128> sABCMask = CreateASCIIMask(TestABC);
+// ...
+// if (someChar < 128 && sABCMask[someChar]) this is A or B or C
+
+
+namespace details
+{
+template<typename F, size_t... Indices>
+constexpr std::array<bool, 128> CreateASCIIMask(F fun, mozilla::IndexSequence<Indices...>)
+{
+  return {{ fun(Indices)... }};
+}
+} // namespace details
+
+template<typename F>
+constexpr std::array<bool, 128> CreateASCIIMask(F fun)
+{
+  return details::CreateASCIIMask(fun, mozilla::MakeIndexSequence<128>::Type{});
+}
+
+} // namespace mozilla
+
+#endif // nsASCIIMask_h_

xpcom/tests/gtest/TestStrings.cpp

@@ -6,6 +6,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include "nsASCIIMask.h"
 #include "nsString.h"
 #include "nsStringBuffer.h"
 #include "nsReadableUtils.h"
@@ -1088,6 +1089,53 @@ TEST(Strings, Split)
   EXPECT_EQ(counter, (size_t)2);
 }
 
+constexpr bool TestSomeChars(char c)
+{
+  return c == 'a' || c == 'c' || c == 'e' || c == '7' ||
+         c == 'G' || c == 'Z' || c == '\b' || c == '?';
+}
+TEST(Strings,ASCIIMask)
+{
+  const ASCIIMaskArray& maskCRLF = mozilla::ASCIIMask::MaskCRLF();
+  EXPECT_TRUE(maskCRLF['\n'] && mozilla::ASCIIMask::IsMasked(maskCRLF, '\n'));
+  EXPECT_TRUE(maskCRLF['\r'] && mozilla::ASCIIMask::IsMasked(maskCRLF, '\r'));
+  EXPECT_FALSE(maskCRLF['g'] || mozilla::ASCIIMask::IsMasked(maskCRLF, 'g'));
+  EXPECT_FALSE(maskCRLF[' '] || mozilla::ASCIIMask::IsMasked(maskCRLF, ' '));
+  EXPECT_FALSE(maskCRLF['\0'] || mozilla::ASCIIMask::IsMasked(maskCRLF, '\0'));
+  EXPECT_FALSE(mozilla::ASCIIMask::IsMasked(maskCRLF, 14324));
+
+  const ASCIIMaskArray& mask0to9 = mozilla::ASCIIMask::Mask0to9();
+  EXPECT_TRUE(mask0to9['9'] && mozilla::ASCIIMask::IsMasked(mask0to9, '9'));
+  EXPECT_TRUE(mask0to9['0'] && mozilla::ASCIIMask::IsMasked(mask0to9, '0'));
+  EXPECT_TRUE(mask0to9['4'] && mozilla::ASCIIMask::IsMasked(mask0to9, '4'));
+  EXPECT_FALSE(mask0to9['g'] || mozilla::ASCIIMask::IsMasked(mask0to9, 'g'));
+  EXPECT_FALSE(mask0to9[' '] || mozilla::ASCIIMask::IsMasked(mask0to9, ' '));
+  EXPECT_FALSE(mask0to9['\n'] || mozilla::ASCIIMask::IsMasked(mask0to9, '\n'));
+  EXPECT_FALSE(mask0to9['\0'] || mozilla::ASCIIMask::IsMasked(mask0to9, '\0'));
+  EXPECT_FALSE(mozilla::ASCIIMask::IsMasked(maskCRLF, 14324));
+
+  const ASCIIMaskArray& maskWS = mozilla::ASCIIMask::MaskWhitespace();
+  EXPECT_TRUE(maskWS[' '] && mozilla::ASCIIMask::IsMasked(maskWS, ' '));
+  EXPECT_TRUE(maskWS['\t'] && mozilla::ASCIIMask::IsMasked(maskWS, '\t'));
+  EXPECT_FALSE(maskWS['8'] || mozilla::ASCIIMask::IsMasked(maskWS, '8'));
+  EXPECT_FALSE(maskWS['\0'] || mozilla::ASCIIMask::IsMasked(maskWS, '\0'));
+  EXPECT_FALSE(mozilla::ASCIIMask::IsMasked(maskCRLF, 14324));
+
+  constexpr ASCIIMaskArray maskSome = mozilla::CreateASCIIMask(TestSomeChars);
+  EXPECT_TRUE(maskSome['a'] && mozilla::ASCIIMask::IsMasked(maskSome, 'a'));
+  EXPECT_TRUE(maskSome['c'] && mozilla::ASCIIMask::IsMasked(maskSome, 'c'));
+  EXPECT_TRUE(maskSome['e'] && mozilla::ASCIIMask::IsMasked(maskSome, 'e'));
+  EXPECT_TRUE(maskSome['7'] && mozilla::ASCIIMask::IsMasked(maskSome, '7'));
+  EXPECT_TRUE(maskSome['G'] && mozilla::ASCIIMask::IsMasked(maskSome, 'G'));
+  EXPECT_TRUE(maskSome['Z'] && mozilla::ASCIIMask::IsMasked(maskSome, 'Z'));
+  EXPECT_TRUE(maskSome['\b'] && mozilla::ASCIIMask::IsMasked(maskSome, '\b'));
+  EXPECT_TRUE(maskSome['?'] && mozilla::ASCIIMask::IsMasked(maskSome, '?'));
+  EXPECT_FALSE(maskSome['8'] || mozilla::ASCIIMask::IsMasked(maskSome, '8'));
+  EXPECT_FALSE(maskSome['\0'] || mozilla::ASCIIMask::IsMasked(maskSome, '\0'));
+  EXPECT_FALSE(mozilla::ASCIIMask::IsMasked(maskCRLF, 14324));
+}
+
+
 template <typename T> void
 CompressWhitespaceHelper()
 {