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Formalise IndirectNoBase and permit a knowledgable caller to avoid conditionals.

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Thomas Harte 2022-03-09 20:19:40 -05:00
parent c1cc4f96df
commit 520baa6ec8
1 changed files with 51 additions and 16 deletions
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67
InstructionSets/x86/Instruction.hpp
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@ -201,15 +201,19 @@ enum class Operation: uint8_t {
/// Load AL with DS:[AL+BX].
XLAT,
// TODO: expand detail on all operations below.
//
// 80186 additions.
//
/// Checks an array index against bounds.
/// Checks whether the signed value in the destination register is within the bounds
/// stored at the location indicated by the source register, which will point to two
/// 16- or 32-bit words, the first being a signed lower bound and the signed upper.
/// Raises a bounds exception if not.
BOUND,
// TODO: expand detail on all operations below.
/// Create stack frame.
ENTER,
/// Procedure exit; copies BP to SP, then pops a new BP from the stack.
@ -326,9 +330,15 @@ enum class Operation: uint8_t {
/// Two-operand form of IMUL; multiply the source by the destination and write to the destination.
IMUL_2,
// Various conditional sets; each sets the byte at the location given by the operand
// to $ff if the condition is met; $00 otherwise.
SETO, SETNO, SETB, SETNB, SETZ, SETNZ, SETBE, SETNBE,
SETS, SETNS, SETP, SETNP, SETL, SETNL, SETLE, SETNLE,
// Various special-case moves (i.e. those where it is impractical to extend the
// Source enum, so the requirement for special handling is loaded into the operation).
// In all cases the Cx, Dx and Tx Source aliases can be used to reinterpret the relevant
// source or destination.
MOVtoCr, MOVfromCr,
MOVtoDr, MOVfromDr,
MOVtoTr, MOVfromTr,
@ -392,6 +402,11 @@ enum class Source: uint8_t {
eSI = eSIorDH, DH = eSIorDH,
eDI = eDIorBH, BH = eDIorBH,
// Aliases for control, test and debug registers.
C0 = 0, C1 = 1, C2 = 2, C3 = 3, C4 = 4, C5 = 5, C6 = 6, C7 = 7,
T0 = 0, T1 = 1, T2 = 2, T3 = 3, T4 = 4, T5 = 5, T6 = 6, T7 = 7,
D0 = 0, D1 = 1, D2 = 2, D3 = 3, D4 = 4, D5 = 5, D6 = 6, D7 = 7,
// Selectors.
ES, CS, SS, DS, FS, GS,
@ -403,8 +418,6 @@ enum class Source: uint8_t {
/// The address included within this instruction should be used as the source.
DirectAddress,
// TODO: is this better eliminated in favour of an indirect
// source with a base() and index() of 0?
/// The immediate value included within this instruction should be used as the source.
Immediate,
@ -414,8 +427,12 @@ enum class Source: uint8_t {
// Elsewhere, as an implementation detail, the low three bits of an indirect source
// are reused; (Indirect-1) is also used as a sentinel value but is not a valid member
// of the enum and isn't exposed externally.
/// The ScaleIndexBase associated with this source should be used, but
/// its base should be ignored (and is guaranteed to be zero if the default
/// getter is used).
IndirectNoBase = Indirect - 1,
};
constexpr Source SourceIndirectNoBase = Source(uint8_t(Source::Indirect) - 1);
enum class Repetition: uint8_t {
None, RepE, RepNE
@ -436,7 +453,12 @@ class ScaleIndexBase {
public:
constexpr ScaleIndexBase() noexcept {}
constexpr ScaleIndexBase(uint8_t sib) noexcept : sib_(sib) {}
constexpr ScaleIndexBase(int scale, Source index, Source base) noexcept : sib_(uint8_t(scale << 6 | (int(index != Source::None ? index : Source::eSI) << 3) | int(base))) {}
constexpr ScaleIndexBase(int scale, Source index, Source base) noexcept :
sib_(uint8_t(
scale << 6 |
(int(index != Source::None ? index : Source::eSI) << 3) |
int(base)
)) {}
constexpr ScaleIndexBase(Source index, Source base) noexcept : ScaleIndexBase(0, index, base) {}
constexpr explicit ScaleIndexBase(Source base) noexcept : ScaleIndexBase(0, Source::None, base) {}
@ -459,6 +481,10 @@ class ScaleIndexBase {
return Source(sib_ & 0x7);
}
constexpr uint8_t without_base() const {
return sib_ & ~0x3;
}
bool operator ==(const ScaleIndexBase &rhs) const {
// Permit either exact equality or index and base being equal
// but transposed with a scale of 1.
@ -501,20 +527,26 @@ class DataPointer {
constexpr DataPointer(Source source, ScaleIndexBase sib) noexcept : source_(source), sib_(sib) {}
/// Constructs an indirect DataPointer referencing the given base, index and scale.
/// Automatically maps Source::Indirect to Source::IndirectNoBase if base is Source::None.
constexpr DataPointer(Source base, Source index, int scale) noexcept :
source_(base != Source::None ? Source::Indirect : SourceIndirectNoBase),
source_(base != Source::None ? Source::Indirect : Source::IndirectNoBase),
sib_(scale, index, base) {}
constexpr bool operator ==(const DataPointer &rhs) const {
// Require a SIB match only if source_ is ::Indirect or ::IndirectNoBase.
return source_ == rhs.source_ && (source_ < SourceIndirectNoBase || sib_ == rhs.sib_);
return
source_ == rhs.source_ && (
source_ < Source::IndirectNoBase ||
(source_ == Source::Indirect && sib_ == rhs.sib_) ||
(source_ == Source::IndirectNoBase && sib_.without_base() == rhs.sib_.without_base())
);
}
// TODO: determine whether conditionals below
// have introduced branching.
constexpr Source source() const {
return (source_ >= SourceIndirectNoBase) ? Source::Indirect : source_;
template <bool obscure_indirectNoBase = false> constexpr Source source() const {
if constexpr (obscure_indirectNoBase) {
return (source_ >= Source::IndirectNoBase) ? Source::Indirect : source_;
}
return source_;
}
constexpr int scale() const {
@ -525,8 +557,11 @@ class DataPointer {
return sib_.index();
}
constexpr Source base() const {
return (source_ <= SourceIndirectNoBase) ? Source::None : sib_.base();
template <bool obscure_indirectNoBase = false> constexpr Source base() const {
if constexpr (obscure_indirectNoBase) {
return (source_ <= Source::IndirectNoBase) ? Source::None : sib_.base();
}
return sib_.base();
}
private: