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Conclusion: a union does produce better code.

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(But needn't be so verbose)
This commit is contained in:
Thomas Harte 2022-04-29 04:51:02 -04:00
parent 727a14c6f9
commit 824d3ae3f7
2 changed files with 290 additions and 267 deletions
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501
InstructionSets/M68k/Implementation/PerformImplementation.hpp
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File diff suppressed because it is too large Load Diff

56
Numeric/RegisterSizes.hpp
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@ -11,17 +11,19 @@
#include <cstdint>
#pragma pack(push, 1)
// Unions below assume a modern consumer architecture,
// and that this compiler offers C-style anonymous structs.
namespace CPU {
/// Provides a union that — on most compilers for modern consumer architectures,
/// and therefore this project assumes universally — provides access to the low and
/// high halves of some larger integer type.
/// Provides access to all intermediate parts of a larger int.
template <typename Full, typename Half> union RegisterPair {
RegisterPair(Full v) : full(v) {}
RegisterPair() {}
Full full;
#pragma pack(push, 1)
#if TARGET_RT_BIG_ENDIAN
struct {
Half high, low;
@ -31,12 +33,52 @@ template <typename Full, typename Half> union RegisterPair {
Half low, high;
} halves;
#endif
#pragma pack(pop)
};
typedef RegisterPair<uint16_t, uint8_t> RegisterPair16;
typedef RegisterPair<uint32_t, RegisterPair16> RegisterPair32;
using RegisterPair16 = RegisterPair<uint16_t, uint8_t>;
using RegisterPair32 = RegisterPair<uint32_t, RegisterPair16>;
/// Provides access to lower portions of a larger int.
template <typename IntT> union SlicedInt {};
template <> union SlicedInt<uint16_t> {
struct {
uint16_t w;
};
struct {
#if TARGET_RT_BIG_ENDIAN
uint8_t __padding[1];
#endif
uint8_t b;
};
};
template <> union SlicedInt<uint32_t> {
struct {
uint32_t l;
};
struct {
#if TARGET_RT_BIG_ENDIAN
uint16_t __padding[1];
#endif
uint16_t w;
};
struct {
#if TARGET_RT_BIG_ENDIAN
uint8_t __padding[3];
#endif
uint8_t b;
};
};
using SlicedInt16 = SlicedInt<uint16_t>;
using SlicedInt32 = SlicedInt<uint32_t>;
}
#pragma pack(pop)
#endif /* RegisterSizes_hpp */