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third_party
skia
src
base
SkUtils.h
Go to the documentation of this file.
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/*
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* Copyright 2006 The Android Open Source Project
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkUtils_DEFINED
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#define SkUtils_DEFINED
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#include "
include/private/base/SkAttributes.h
"
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#include <cstring>
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#include <type_traits>
// is_trivially_copyable
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namespace
SkHexadecimalDigits
{
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extern
const
char
gUpper
[16];
// 0-9A-F
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extern
const
char
gLower
[16];
// 0-9a-f
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}
// namespace SkHexadecimalDigits
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///////////////////////////////////////////////////////////////////////////////
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// If T is an 8-byte GCC or Clang vector extension type, it would naturally pass or return in the
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// MMX mm0 register on 32-bit x86 builds. This has the fun side effect of clobbering any state in
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// the x87 st0 register. (There is no ABI governing who should preserve mm?/st? registers, so no
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// one does!)
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//
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// We force-inline sk_unaligned_load() and sk_unaligned_store() to avoid that, making them safe to
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// use for all types on all platforms, thus solving the problem once and for all!
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// A separate problem exists with 32-bit x86. The default calling convention returns values in
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// ST0 (the x87 FPU). Unfortunately, doing so can mutate some bit patterns (signaling NaNs
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// become quiet). If you're using these functions to pass data around as floats, but it's actually
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// integers, that can be bad -- raster pipeline does this.
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//
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// With GCC and Clang, the always_inline attribute ensures we don't have a problem. MSVC, though,
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// ignores __forceinline in debug builds, so the return-via-ST0 is always present. Switching to
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// __vectorcall changes the functions to return in xmm0.
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#if defined(_MSC_VER) && defined(_M_IX86)
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#define SK_FP_SAFE_ABI __vectorcall
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#else
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#define SK_FP_SAFE_ABI
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#endif
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template
<
typename
T,
typename
P>
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static
SK_ALWAYS_INLINE
T
SK_FP_SAFE_ABI
sk_unaligned_load
(
const
P* ptr) {
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static_assert
(std::is_trivially_copyable_v<P> || std::is_void_v<P>);
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static_assert
(std::is_trivially_copyable_v<T>);
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T
val;
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// gcc's class-memaccess sometimes triggers when:
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// - `T` is trivially copyable but
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// - `T` is non-trivial (e.g. at least one eligible default constructor is
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// non-trivial).
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// Use `reinterpret_cast<const void*>` to explicit suppress this warning; a
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// trivially copyable type is safe to memcpy from/to.
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memcpy(&val,
static_cast<
const
void
*
>
(ptr),
sizeof
(val));
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return
val;
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}
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template
<
typename
T,
typename
P>
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static
SK_ALWAYS_INLINE
void
SK_FP_SAFE_ABI
sk_unaligned_store
(P* ptr,
T
val) {
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static_assert
(std::is_trivially_copyable<T>::value);
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memcpy(ptr, &val,
sizeof
(val));
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}
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// Copy the bytes from src into an instance of type Dst and return it.
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template
<
typename
Dst,
typename
Src>
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static
SK_ALWAYS_INLINE
Dst
SK_FP_SAFE_ABI
sk_bit_cast
(
const
Src& src) {
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static_assert
(
sizeof
(Dst) ==
sizeof
(Src));
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static_assert
(std::is_trivially_copyable<Dst>::value);
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static_assert
(std::is_trivially_copyable<Src>::value);
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return
sk_unaligned_load<Dst>(&src);
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}
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#undef SK_FP_SAFE_ABI
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#endif
SkAttributes.h
SK_ALWAYS_INLINE
#define SK_ALWAYS_INLINE
Definition
SkAttributes.h:30
sk_unaligned_load
static SK_ALWAYS_INLINE T SK_FP_SAFE_ABI sk_unaligned_load(const P *ptr)
Definition
SkUtils.h:46
SK_FP_SAFE_ABI
#define SK_FP_SAFE_ABI
Definition
SkUtils.h:42
sk_bit_cast
static SK_ALWAYS_INLINE Dst SK_FP_SAFE_ABI sk_bit_cast(const Src &src)
Definition
SkUtils.h:68
sk_unaligned_store
static SK_ALWAYS_INLINE void SK_FP_SAFE_ABI sk_unaligned_store(P *ptr, T val)
Definition
SkUtils.h:61
SkHexadecimalDigits
Definition
SkUtils.h:16
SkHexadecimalDigits::gUpper
const char gUpper[16]
Definition
SkUtils.cpp:10
SkHexadecimalDigits::gLower
const char gLower[16]
Definition
SkUtils.cpp:12
T
#define T
Definition
precompiler.cc:65
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