Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 126 insertions, 0 deletions

diff --git a/mfbt/TemplateLib.h b/mfbt/TemplateLib.h
new file mode 100644
index 0000000000..8c620390b3
--- /dev/null
+++ b/mfbt/TemplateLib.h
@@ -0,0 +1,126 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+/*
+ * Reusable template meta-functions on types and compile-time values.  Meta-
+ * functions are placed inside the 'tl' namespace to avoid conflict with non-
+ * meta functions of the same name (e.g., mozilla::tl::FloorLog2 vs.
+ * mozilla::FloorLog2).
+ *
+ * When constexpr support becomes universal, we should probably use that instead
+ * of some of these templates, for simplicity.
+ */
+
+#ifndef mozilla_TemplateLib_h
+#define mozilla_TemplateLib_h
+
+#include <limits.h>
+#include <stddef.h>
+#include <type_traits>
+
+namespace mozilla {
+
+namespace tl {
+
+/** Compute min/max. */
+template <size_t Size, size_t... Rest>
+struct Min {
+  static constexpr size_t value =
+      Size < Min<Rest...>::value ? Size : Min<Rest...>::value;
+};
+
+template <size_t Size>
+struct Min<Size> {
+  static constexpr size_t value = Size;
+};
+
+template <size_t Size, size_t... Rest>
+struct Max {
+  static constexpr size_t value =
+      Size > Max<Rest...>::value ? Size : Max<Rest...>::value;
+};
+
+template <size_t Size>
+struct Max<Size> {
+  static constexpr size_t value = Size;
+};
+
+/** Compute floor(log2(i)). */
+template <size_t I>
+struct FloorLog2 {
+  static const size_t value = 1 + FloorLog2<I / 2>::value;
+};
+template <>
+struct FloorLog2<0> { /* Error */
+};
+template <>
+struct FloorLog2<1> {
+  static const size_t value = 0;
+};
+
+/** Compute ceiling(log2(i)). */
+template <size_t I>
+struct CeilingLog2 {
+  static const size_t value = FloorLog2<2 * I - 1>::value;
+};
+
+/** Round up to the nearest power of 2. */
+template <size_t I>
+struct RoundUpPow2 {
+  static const size_t value = size_t(1) << CeilingLog2<I>::value;
+};
+template <>
+struct RoundUpPow2<0> {
+  static const size_t value = 1;
+};
+
+/** Compute the number of bits in the given unsigned type. */
+template <typename T>
+struct BitSize {
+  static const size_t value = sizeof(T) * CHAR_BIT;
+};
+
+/**
+ * Produce an N-bit mask, where N <= BitSize<size_t>::value.  Handle the
+ * language-undefined edge case when N = BitSize<size_t>::value.
+ */
+template <size_t N>
+struct NBitMask {
+  // Assert the precondition.  On success this evaluates to 0.  Otherwise it
+  // triggers divide-by-zero at compile time: a guaranteed compile error in
+  // C++11, and usually one in C++98.  Add this value to |value| to assure
+  // its computation.
+  static const size_t checkPrecondition =
+      0 / size_t(N < BitSize<size_t>::value);
+  static const size_t value = (size_t(1) << N) - 1 + checkPrecondition;
+};
+template <>
+struct NBitMask<BitSize<size_t>::value> {
+  static const size_t value = size_t(-1);
+};
+
+/**
+ * For the unsigned integral type size_t, compute a mask M for N such that
+ * for all X, !(X & M) implies X * N will not overflow (w.r.t size_t)
+ */
+template <size_t N>
+struct MulOverflowMask {
+  static const size_t value =
+      ~NBitMask<BitSize<size_t>::value - CeilingLog2<N>::value>::value;
+};
+template <>
+struct MulOverflowMask<0> { /* Error */
+};
+template <>
+struct MulOverflowMask<1> {
+  static const size_t value = 0;
+};
+
+}  // namespace tl
+
+}  // namespace mozilla
+
+#endif /* mozilla_TemplateLib_h */