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author | Lorry Tar Creator <lorry-tar-importer@baserock.org> | 2013-12-11 22:24:18 +0000 |
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committer | <> | 2014-07-24 09:30:59 +0000 |
commit | 59e2936f588aa945e8dcd6c737523c299067e9d0 (patch) | |
tree | 97e74980cc54baa19de5faa11f5a50a0121a48ea /mfbt/PodOperations.h | |
download | mozjs24-master.tar.gz |
Imported from /home/lorry/working-area/delta_mozilla_mozjs24/mozjs-24.2.0.tar.bz2.HEADmozjs-24.2.0master
Diffstat (limited to 'mfbt/PodOperations.h')
-rw-r--r-- | mfbt/PodOperations.h | 159 |
1 files changed, 159 insertions, 0 deletions
diff --git a/mfbt/PodOperations.h b/mfbt/PodOperations.h new file mode 100644 index 0000000..6c6af27 --- /dev/null +++ b/mfbt/PodOperations.h @@ -0,0 +1,159 @@ +/* -*- Mode: C++; tab-width: 2; 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/. */ + +/* + * 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/Attributes.h" +#include "mozilla/Util.h" + +#include <string.h> + +namespace mozilla { + +/** Set the contents of |t| to 0. */ +template<typename T> +static void +PodZero(T* t) +{ + memset(t, 0, sizeof(T)); +} + +/** Set the contents of |nelem| elements starting at |t| to 0. */ +template<typename T> +static 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 void +PodArrayZero(T (&t)[N]) +{ + memset(t, 0, N * sizeof(T)); +} + +/** + * Assign |*src| to |*dst|. The locations must not be the same and must not + * overlap. + */ +template<typename T> +static 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> +MOZ_ALWAYS_INLINE static 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> +MOZ_ALWAYS_INLINE static 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 void +PodArrayCopy(T (&dst)[N], const T (&src)[N]) +{ + PodCopy(dst, src, N); +} + +/** + * Determine whether the |len| elements at |one| are memory-identical to the + * |len| elements at |two|. + */ +template<typename T> +MOZ_ALWAYS_INLINE static 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_ |