diff -r 000000000000 -r 6474c204b198 mfbt/PodOperations.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mfbt/PodOperations.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,184 @@
+/* -*- 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/. */
+
+/*
+ * Operations for zeroing POD types, arrays, and so on.
+ *
+ * These operations are preferable to memset, memcmp, and the like because they
+ * don't require remembering to multiply by sizeof(T), array lengths, and so on
+ * everywhere.
+ */
+
+#ifndef mozilla_PodOperations_h
+#define mozilla_PodOperations_h
+
+#include "mozilla/Array.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Attributes.h"
+
+#include <stdint.h>
+#include <string.h>
+
+namespace mozilla {
+
+/** Set the contents of |t| to 0. */
+template<typename T>
+static MOZ_ALWAYS_INLINE void
+PodZero(T* t)
+{
+  memset(t, 0, sizeof(T));
+}
+
+/** Set the contents of |nelem| elements starting at |t| to 0. */
+template<typename T>
+static MOZ_ALWAYS_INLINE void
+PodZero(T* t, size_t nelem)
+{
+  /*
+   * This function is often called with 'nelem' small; we use an inline loop
+   * instead of calling 'memset' with a non-constant length.  The compiler
+   * should inline the memset call with constant size, though.
+   */
+  for (T* end = t + nelem; t < end; t++)
+    memset(t, 0, sizeof(T));
+}
+
+/*
+ * Arrays implicitly convert to pointers to their first element, which is
+ * dangerous when combined with the above PodZero definitions.  Adding an
+ * overload for arrays is ambiguous, so we need another identifier.  The
+ * ambiguous overload is left to catch mistaken uses of PodZero; if you get a
+ * compile error involving PodZero and array types, use PodArrayZero instead.
+ */
+template<typename T, size_t N>
+static void PodZero(T (&t)[N]) MOZ_DELETE;
+template<typename T, size_t N>
+static void PodZero(T (&t)[N], size_t nelem) MOZ_DELETE;
+
+/** Set the contents of the array |t| to zero. */
+template <class T, size_t N>
+static MOZ_ALWAYS_INLINE void
+PodArrayZero(T (&t)[N])
+{
+  memset(t, 0, N * sizeof(T));
+}
+
+template <typename T, size_t N>
+static MOZ_ALWAYS_INLINE void
+PodArrayZero(Array<T, N>& arr)
+{
+  memset(&arr[0], 0, N * sizeof(T));
+}
+
+/**
+ * Assign |*src| to |*dst|.  The locations must not be the same and must not
+ * overlap.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE void
+PodAssign(T* dst, const T* src)
+{
+  MOZ_ASSERT(dst != src);
+  MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= 1);
+  MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= 1);
+  memcpy(reinterpret_cast<char*>(dst), reinterpret_cast<const char*>(src), sizeof(T));
+}
+
+/**
+ * Copy |nelem| T elements from |src| to |dst|.  The two memory ranges must not
+ * overlap!
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE void
+PodCopy(T* dst, const T* src, size_t nelem)
+{
+  MOZ_ASSERT(dst != src);
+  MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= nelem);
+  MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= nelem);
+
+  if (nelem < 128) {
+    /*
+     * Avoid using operator= in this loop, as it may have been
+     * intentionally deleted by the POD type.
+     */
+    for (const T* srcend = src + nelem; src < srcend; src++, dst++)
+      PodAssign(dst, src);
+  } else {
+    memcpy(dst, src, nelem * sizeof(T));
+  }
+}
+
+template<typename T>
+static MOZ_ALWAYS_INLINE void
+PodCopy(volatile T* dst, const volatile T* src, size_t nelem)
+{
+  MOZ_ASSERT(dst != src);
+  MOZ_ASSERT_IF(src < dst,
+                PointerRangeSize(src, static_cast<const volatile T*>(dst)) >= nelem);
+  MOZ_ASSERT_IF(dst < src,
+                PointerRangeSize(static_cast<const volatile T*>(dst), src) >= nelem);
+
+  /*
+   * Volatile |dst| requires extra work, because it's undefined behavior to
+   * modify volatile objects using the mem* functions.  Just write out the
+   * loops manually, using operator= rather than memcpy for the same reason,
+   * and let the compiler optimize to the extent it can.
+   */
+  for (const volatile T* srcend = src + nelem; src < srcend; src++, dst++)
+    *dst = *src;
+}
+
+/*
+ * Copy the contents of the array |src| into the array |dst|, both of size N.
+ * The arrays must not overlap!
+ */
+template <class T, size_t N>
+static MOZ_ALWAYS_INLINE void
+PodArrayCopy(T (&dst)[N], const T (&src)[N])
+{
+  PodCopy(dst, src, N);
+}
+
+/**
+ * Copy the memory for |nelem| T elements from |src| to |dst|.  If the two
+ * memory ranges overlap, then the effect is as if the |nelem| elements are
+ * first copied from |src| to a temporary array, and then from the temporary
+ * array to |dst|.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE void
+PodMove(T* dst, const T* src, size_t nelem)
+{
+  MOZ_ASSERT(nelem <= SIZE_MAX / sizeof(T),
+             "trying to move an impossible number of elements");
+  memmove(dst, src, nelem * sizeof(T));
+}
+
+/**
+ * Determine whether the |len| elements at |one| are memory-identical to the
+ * |len| elements at |two|.
+ */
+template<typename T>
+static MOZ_ALWAYS_INLINE bool
+PodEqual(const T* one, const T* two, size_t len)
+{
+  if (len < 128) {
+    const T* p1end = one + len;
+    const T* p1 = one;
+    const T* p2 = two;
+    for (; p1 < p1end; p1++, p2++) {
+      if (*p1 != *p2)
+        return false;
+    }
+    return true;
+  }
+
+  return !memcmp(one, two, len * sizeof(T));
+}
+
+} // namespace mozilla
+
+#endif /* mozilla_PodOperations_h */