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Merge pull request #270 from neobrain/bitfield_fixes

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Bitfield fixes
This commit is contained in:
Pierre Bourdon 2014-04-14 20:24:01 +02:00
commit fc71494742
2 changed files with 58 additions and 3 deletions
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19
Source/Core/Common/BitField.h
View File

@ -36,6 +36,8 @@
#include <limits>
#include <type_traits>
#include "Common.h"
/*
* Abstract bitfield class
*
@ -92,13 +94,23 @@
*
* Caveats:
*
* 1)
* BitField provides automatic casting from and to the storage type where
* appropriate. However, when using non-typesafe functions like printf, an
* explicit cast must be performed on the BitField object to make sure it gets
* passed correctly, e.g.:
* printf("Value: %d", (s32)some_register.some_signed_fields);
*
* 2)
* Not really a caveat, but potentially irritating: This class is used in some
* packed structures that do not guarantee proper alignment. Therefore we have
* to use #pragma pack here not to pack the members of the class, but instead
* to break GCC's assumption that the members of the class are aligned on
* sizeof(StorageType).
* TODO(neobrain): Confirm that this is a proper fix and not just masking
* symptoms.
*/
#pragma pack(1)
template<std::size_t position, std::size_t bits, typename T>
struct BitField
{
@ -113,13 +125,13 @@ public:
// so that we can use this within unions
BitField() = default;
BitField& operator=(T val)
__forceinline BitField& operator=(T val)
{
storage = (storage & ~GetMask()) | ((val << position) & GetMask());
return *this;
}
operator T() const
__forceinline operator T() const
{
if (std::numeric_limits<T>::is_signed)
{
@ -144,7 +156,7 @@ private:
// Unsigned version of StorageType
typedef typename std::make_unsigned<StorageType>::type StorageTypeU;
StorageType GetMask() const
__forceinline StorageType GetMask() const
{
return ((~(StorageTypeU)0) >> (8*sizeof(T) - bits)) << position;
}
@ -158,3 +170,4 @@ private:
static_assert(bits <= 8 * sizeof(T), "Invalid number of bits");
static_assert(bits > 0, "Invalid number of bits");
};
#pragma pack()

42
Source/UnitTests/Common/BitFieldTest.cpp
View File

@ -125,3 +125,45 @@ TEST(BitField, Assignment)
EXPECT_EQ(object.regular_field_unsigned, object.at_dword_boundary);
}
}
// Test class behavior on oddly aligned structures.
TEST(BitField, Alignment)
{
#pragma pack(1)
struct OddlyAlignedTestStruct
{
u8 padding;
TestUnion obj;
};
#pragma pack()
GC_ALIGNED16(OddlyAlignedTestStruct test_struct);
TestUnion& object = test_struct.obj;
static_assert(alignof(test_struct.obj.signed_1bit) == 1, "Incorrect variable alignment");
for (u64 val : table)
{
// Assignments with fixed values
object.full_u64 = val;
EXPECT_EQ(val, object.full_u64);
object.full_s64 = (s64)val;
EXPECT_EQ((s64)val, object.full_u64);
object.regular_field_unsigned = val;
EXPECT_EQ(val & 0x7, object.regular_field_unsigned);
object.at_dword_boundary = val;
EXPECT_EQ(((s64)(val << 60)) >> 60, object.at_dword_boundary);
object.signed_1bit = val;
EXPECT_EQ((val & 1) ? -1 : 0, object.signed_1bit);
object.regular_field_signed = val;
EXPECT_EQ(((s64)(object.hex << 61)) >> 61, object.regular_field_signed);
// Assignment from other BitField
object.at_dword_boundary = object.regular_field_unsigned;
EXPECT_EQ(object.regular_field_unsigned, object.at_dword_boundary);
}
}