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Relocate and clarify barrel shifts.
With a view to independent testing.
This commit is contained in:
Thomas Harte
parent
9b42d35d56
commit
c49b26701f
122
InstructionSets/ARM/BarrelShifter.hpp
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122
InstructionSets/ARM/BarrelShifter.hpp
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@ -0,0 +1,122 @@
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//
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// BarrelShifter.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 28/02/2024.
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// Copyright © 2024 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace InstructionSet::ARM {
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enum class ShiftType {
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LogicalLeft = 0b00,
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LogicalRight = 0b01,
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ArithmeticRight = 0b10,
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RotateRight = 0b11,
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};
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template <bool writeable> struct Carry;
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template <> struct Carry<true> {
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using type = uint32_t &;
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};
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template <> struct Carry<false> {
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using type = uint32_t;
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};
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/// Apply a rotation of @c type to @c source of @c amount; @c carry should be either @c 1 or @c 0
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/// at call to represent the current value of the carry flag. If @c set_carry is @c true then @c carry will
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/// receive the new value of the carry flag following the rotation — @c 0 for no carry, @c non-0 for carry.
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template <ShiftType type, bool set_carry>
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void shift(uint32_t &source, uint32_t amount, typename Carry<set_carry>::type carry) {
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switch(type) {
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case ShiftType::LogicalLeft:
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if(amount > 32) {
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if constexpr (set_carry) carry = 0;
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source = 0;
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} else if(amount == 32) {
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if constexpr (set_carry) carry = source & 1;
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source = 0;
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} else if(amount > 0) {
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if constexpr (set_carry) carry = source & (0x8000'0000 >> (amount - 1));
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source <<= amount;
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}
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break;
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case ShiftType::LogicalRight:
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if(amount > 32) {
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if constexpr (set_carry) carry = 0;
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source = 0;
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} else if(amount == 32) {
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if constexpr (set_carry) carry = source & 0x8000'0000;
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source = 0;
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} else if(amount > 0) {
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if constexpr (set_carry) carry = source & (1 << (amount - 1));
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source >>= amount;
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} else {
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// A logical shift right by '0' is treated as a shift by 32;
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// assemblers are supposed to map LSR #0 to LSL #0.
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if constexpr (set_carry) carry = source & 0x8000'0000;
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source = 0;
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}
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break;
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case ShiftType::ArithmeticRight: {
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const uint32_t sign = (source & 0x8000'0000) ? 0xffff'ffff : 0x0000'0000;
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if(amount >= 32) {
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if constexpr (set_carry) carry = sign;
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source = sign;
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} else if(amount > 0) {
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if constexpr (set_carry) carry = source & (1 << (amount - 1));
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source = (source >> amount) | (sign << (32 - amount));
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} else {
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// As per logical right, an arithmetic shift of '0' is
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// treated as a shift by 32.
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if constexpr (set_carry) carry = source & 0x8000'0000;
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source = sign;
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}
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} break;
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case ShiftType::RotateRight: {
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if(amount == 32) {
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if constexpr (set_carry) carry = source & 0x8000'0000;
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} else if(amount == 0) {
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// Rotate right by 0 is treated as a rotate right by 1 through carry.
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const uint32_t high = carry << 31;
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if constexpr (set_carry) carry = source & 1;
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source = (source >> 1) | high;
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} else {
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amount &= 31;
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if constexpr (set_carry) carry = source & (1 << (amount - 1));
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source = (source >> amount) | (source << (32 - amount));
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}
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} break;
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// TODO: upon adoption of C++20, use std::rotr.
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default: break;
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}
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}
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/// Acts as per @c shift above, but applies runtime shift-type selection.
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template <bool set_carry>
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void shift(ShiftType type, uint32_t &source, uint32_t amount, typename Carry<set_carry>::type carry) {
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switch(type) {
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case ShiftType::LogicalLeft:
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shift<ShiftType::LogicalLeft, set_carry>(source, amount, carry);
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break;
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case ShiftType::LogicalRight:
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shift<ShiftType::LogicalRight, set_carry>(source, amount, carry);
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break;
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case ShiftType::ArithmeticRight:
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shift<ShiftType::ArithmeticRight, set_carry>(source, amount, carry);
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break;
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case ShiftType::RotateRight:
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shift<ShiftType::RotateRight, set_carry>(source, amount, carry);
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break;
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}
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}
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}
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@ -9,6 +9,7 @@
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#pragma once
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#include "../../Reflection/Dispatcher.hpp"
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#include "BarrelShifter.hpp"
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namespace InstructionSet::ARM {
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@ -96,13 +97,6 @@ enum class Condition {
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GT, LE, AL, NV,
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};
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enum class ShiftType {
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LogicalLeft = 0b00,
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LogicalRight = 0b01,
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ArithmeticRight = 0b10,
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RotateRight = 0b11,
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};
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//
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// Implementation details.
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//
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@ -1336,6 +1336,7 @@
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4B2005402B804AA300420C5C /* OperationMapper.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = OperationMapper.hpp; sourceTree = "<group>"; };
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4B2005422B804D6400420C5C /* ARMDecoderTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ARMDecoderTests.mm; sourceTree = "<group>"; };
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4B2005462B8BD7A500420C5C /* Registers.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Registers.hpp; sourceTree = "<group>"; };
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4B2005472B8FB13D00420C5C /* BarrelShifter.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = BarrelShifter.hpp; sourceTree = "<group>"; };
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4B2130E0273A7A0A008A77B4 /* Audio.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = Audio.cpp; sourceTree = "<group>"; };
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4B2130E1273A7A0A008A77B4 /* Audio.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Audio.hpp; sourceTree = "<group>"; };
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4B228CD424D773B30077EF25 /* CSScanTarget.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = CSScanTarget.mm; sourceTree = "<group>"; };
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@ -2759,6 +2760,7 @@
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4B20053D2B804A4F00420C5C /* ARM */ = {
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isa = PBXGroup;
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children = (
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4B2005472B8FB13D00420C5C /* BarrelShifter.hpp */,
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4B2005402B804AA300420C5C /* OperationMapper.hpp */,
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4B2005462B8BD7A500420C5C /* Registers.hpp */,
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);
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@ -8,6 +8,7 @@
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#import <XCTest/XCTest.h>
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#include "../../../InstructionSets/ARM/BarrelShifter.hpp"
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#include "../../../InstructionSets/ARM/OperationMapper.hpp"
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#include "../../../InstructionSets/ARM/Registers.hpp"
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#include "../../../Numeric/Carry.hpp"
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@ -16,94 +17,6 @@ using namespace InstructionSet::ARM;
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namespace {
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template <ShiftType type, bool set_carry>
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void shift(uint32_t &source, uint32_t amount, uint32_t *carry = nullptr) {
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switch(type) {
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case ShiftType::LogicalLeft:
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if(amount > 32) {
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if constexpr (set_carry) *carry = 0;
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source = 0;
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} else if(amount == 32) {
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if constexpr (set_carry) *carry = source & 1;
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source = 0;
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} else if(amount > 0) {
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if constexpr (set_carry) *carry = source & (0x8000'0000 >> (amount - 1));
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source <<= amount;
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}
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break;
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case ShiftType::LogicalRight:
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if(amount > 32) {
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if constexpr (set_carry) *carry = 0;
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source = 0;
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} else if(amount == 32) {
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if constexpr (set_carry) *carry = source & 0x8000'0000;
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source = 0;
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} else if(amount > 0) {
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if constexpr (set_carry) *carry = source & (1 << (amount - 1));
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source >>= amount;
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} else {
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// A logical shift right by '0' is treated as a shift by 32;
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// assemblers are supposed to map LSR #0 to LSL #0.
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if constexpr (set_carry) *carry = source & 0x8000'0000;
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source = 0;
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}
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break;
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case ShiftType::ArithmeticRight: {
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const uint32_t sign = (source & 0x8000'0000) ? 0xffff'ffff : 0x0000'0000;
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if(amount >= 32) {
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if constexpr (set_carry) *carry = sign;
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source = sign;
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} else if(amount > 0) {
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if constexpr (set_carry) *carry = source & (1 << (amount - 1));
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source = (source >> amount) | (sign << (32 - amount));
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} else {
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// As per logical right, an arithmetic shift of '0' is
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// treated as a shift by 32.
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if constexpr (set_carry) *carry = source & 0x8000'0000;
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source = sign;
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}
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} break;
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case ShiftType::RotateRight: {
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if(amount == 32) {
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if constexpr (set_carry) *carry = source & 0x8000'0000;
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} else if(amount == 0) {
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// Rotate right by 0 is treated as a rotate right by 1 through carry.
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const uint32_t high = *carry << 31;
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if constexpr (set_carry) *carry = source & 1;
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source = (source >> 1) | high;
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} else {
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amount &= 31;
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if constexpr (set_carry) *carry = source & (1 << (amount - 1));
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source = (source >> amount) | (source << (32 - amount));
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}
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} break;
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default: break;
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}
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}
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template <bool set_carry>
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void shift(ShiftType type, uint32_t &source, uint32_t amount, uint32_t *carry) {
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switch(type) {
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case ShiftType::LogicalLeft:
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shift<ShiftType::LogicalLeft, set_carry>(source, amount, carry);
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break;
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case ShiftType::LogicalRight:
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shift<ShiftType::LogicalRight, set_carry>(source, amount, carry);
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break;
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case ShiftType::ArithmeticRight:
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shift<ShiftType::ArithmeticRight, set_carry>(source, amount, carry);
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break;
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case ShiftType::RotateRight:
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shift<ShiftType::RotateRight, set_carry>(source, amount, carry);
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break;
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}
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}
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struct Scheduler {
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bool should_schedule(Condition condition) {
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return registers_.test(condition);
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@ -138,7 +51,7 @@ struct Scheduler {
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if constexpr (flags.operand2_is_immediate()) {
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operand2 = fields.immediate();
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if(fields.rotate()) {
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shift<ShiftType::RotateRight, shift_sets_carry>(operand2, fields.rotate(), &rotate_carry);
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shift<ShiftType::RotateRight, shift_sets_carry>(operand2, fields.rotate(), rotate_carry);
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}
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} else {
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uint32_t shift_amount;
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@ -167,7 +80,7 @@ struct Scheduler {
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} else {
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operand2 = registers_.active[fields.operand2()];
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}
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shift<shift_sets_carry>(fields.shift_type(), operand2, shift_amount, &rotate_carry);
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shift<shift_sets_carry>(fields.shift_type(), operand2, shift_amount, rotate_carry);
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}
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// Perform the data processing operation.
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