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Decision: operation is not a template parameter. Hence can use condition as fully typed.

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This commit is contained in:
Thomas Harte 2022-04-30 14:08:51 -04:00
parent a86c5ccdc9
commit 52f355db24
3 changed files with 29 additions and 45 deletions
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31
InstructionSets/M68k/Implementation/PerformImplementation.hpp
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@ -28,41 +28,24 @@ namespace M68k {
// TODO: decisions outstanding:
//
// (1) for DBcc, etc, should this receive the opcode in order to decode the conditional,
// or is it a design error to do any _decoding_ here rather than in the decoder? If
// the latter, should the internal cc operations all treat conditional as another
// Q-style operand?
//
// (2) should I reintroduce the BTSTl/BTSTw-type distinctions, given that the only way to
// (1) should I reintroduce the BTSTl/BTSTw-type distinctions, given that the only way to
// determine them otherwise is by operand types and I'm hoping to treat data into
// here as a black box?
//
// (3) to what extent, if any, should this function have responsibility for a MOVEM, MOVEP,
// (2) to what extent, if any, should this function have responsibility for a MOVEM, MOVEP,
// etc? This factoring is inteded to separate the bus interface from internal logic so
// is there much to do here in any case? As currently drafted, something else will
// already have had to check the operation and cue up data.
//
// (4) related to that, should the flow controller actually offer effective address calculation
// and load/stores, along with a flag indicating whether to stop after loads? By the
// magic of templates that'd avoid having a correlated sequencer — for the non-bus-accurate
// 68ks the loads and stores could be performed immediately, for the accurate they could
// be enqueued, then performed, then a second call to perform that now has the data loaded
// could be performed.
//
// (5) is it really helpful for operation to be a template parameter? I'm trying to avoid forcing
// an additional `switch` if it's likely that the caller has already applied one, but does
// that objective justify the syntax overhead for callers that don't inherently have their
// own `switch`? Do the first sort of callers really exist?
template <
Operation operation,
Model model,
typename FlowController
> void perform(CPU::SlicedInt32 &src, CPU::SlicedInt32 &dest, Status &status, FlowController &flow_controller) {
> void perform(Preinstruction instruction, CPU::SlicedInt32 &src, CPU::SlicedInt32 &dest, Status &status, FlowController &flow_controller) {
#define sub_overflow() ((result ^ destination) & (destination ^ source))
#define add_overflow() ((result ^ destination) & ~(destination ^ source))
switch(operation) {
switch(instruction.operation) {
/*
ABCD adds the lowest bytes from the source and destination using BCD arithmetic,
obeying the extend flag.
@ -298,7 +281,7 @@ template <
case Operation::Bccw:
case Operation::Bccl: {
// Test the conditional, treating 'false' as true.
const bool should_branch = status.evaluate_condition(flow_controller.decode_conditional());
const bool should_branch = status.evaluate_condition(instruction.condition());
// Schedule something appropriate, by rewriting the program for this instruction temporarily.
if(should_branch) {
@ -310,7 +293,7 @@ template <
case Operation::DBcc:
// Decide what sort of DBcc this is.
if(!status.evaluate_condition(flow_controller.decode_conditional())) {
if(!status.evaluate_condition(instruction.condition())) {
-- src.w;
if(src.w == 0xffff) {
@ -327,7 +310,7 @@ template <
break;
case Operation::Scc:
dest.b = status.evaluate_condition(src.l) ? 0xff : 0x00;
dest.b = status.evaluate_condition(instruction.condition()) ? 0xff : 0x00;
break;
/*

3
InstructionSets/M68k/Perform.hpp
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@ -27,10 +27,9 @@ struct NullFlowController {
/// branch, or consumes additional cycles due to the particular value of the operands (on the 68000, think DIV or MUL),
/// that'll be notified to the @c flow_controller.
template <
Operation op,
Model model,
typename FlowController
> void perform(CPU::RegisterPair32 &source, CPU::RegisterPair32 &dest, Status &status, FlowController &flow_controller);
> void perform(Preinstruction instruction, CPU::RegisterPair32 &source, CPU::RegisterPair32 &dest, Status &status, FlowController &flow_controller);
}
}

40
InstructionSets/M68k/Status.hpp
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@ -9,6 +9,8 @@
#ifndef InstructionSets_M68k_Status_h
#define InstructionSets_M68k_Status_h
#include "Instruction.hpp"
namespace InstructionSet {
namespace M68k {
@ -70,29 +72,29 @@ struct Status {
return is_supervisor_;
}
/// Evaluates the condition described in the low four bits of @c code
template <typename IntT> bool evaluate_condition(IntT code) {
switch(code & 0xf) {
/// Evaluates @c condition.
bool evaluate_condition(Condition condition) {
switch(condition) {
default:
case 0x00: return true; // true
case 0x01: return false; // false
case 0x02: return zero_result_ && !carry_flag_; // high
case 0x03: return !zero_result_ || carry_flag_; // low or same
case 0x04: return !carry_flag_; // carry clear
case 0x05: return carry_flag_; // carry set
case 0x06: return zero_result_; // not equal
case 0x07: return !zero_result_; // equal
case 0x08: return !overflow_flag_; // overflow clear
case 0x09: return overflow_flag_; // overflow set
case 0x0a: return !negative_flag_; // positive
case 0x0b: return negative_flag_; // negative
case 0x0c: // greater than or equal
case Condition::True: return true;
case Condition::False: return false;
case Condition::High: return zero_result_ && !carry_flag_;
case Condition::LowOrSame: return !zero_result_ || carry_flag_;
case Condition::CarryClear: return !carry_flag_;
case Condition::CarrySet: return carry_flag_;
case Condition::NotEqual: return zero_result_;
case Condition::Equal: return !zero_result_;
case Condition::OverflowClear: return !overflow_flag_;
case Condition::OverflowSet: return overflow_flag_;
case Condition::Positive: return !negative_flag_;
case Condition::Negative: return negative_flag_;
case Condition::GreaterThanOrEqual:
return (negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_);
case 0x0d: // less than
case Condition::LessThan:
return (negative_flag_ && !overflow_flag_) || (!negative_flag_ && overflow_flag_);
case 0x0e: // greater than
case Condition::GreaterThan:
return zero_result_ && ((negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_));
case 0x0f: // less than or equal
case Condition::LessThanOrEqual:
return !zero_result_ || (negative_flag_ && !overflow_flag_) || (!negative_flag_ && overflow_flag_);
}
}