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M6502: Avoid allocating "Tuples" when processing crossed page boundary conditions. (~20% speedup)

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Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2019-05-04 12:44:53 +01:00
parent 87be068e5a
commit fc9263fb3a
1 changed files with 23 additions and 32 deletions
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55
M6502/M6502.cs
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@ -13,6 +13,7 @@ namespace EightBit
private const byte NMIvector = 0xfa; // NMI vector
private readonly Register16 intermediate = new Register16();
private byte crossedPage;
private bool handlingRESET = false;
private bool handlingNMI = false;
@ -627,30 +628,30 @@ namespace EightBit
return Chip.LowByte(address + this.Y);
}
private Tuple<Register16, byte> Address_AbsoluteX()
private Register16 Address_AbsoluteX()
{
var address = this.Address_Absolute();
var page = address.High;
this.crossedPage = address.High;
address.Word += this.X;
return new Tuple<Register16, byte>(address, page);
return address;
}
private Tuple<Register16, byte> Address_AbsoluteY()
private Register16 Address_AbsoluteY()
{
var address = this.Address_Absolute();
var page = address.High;
this.crossedPage = address.High;
address.Word += this.Y;
return new Tuple<Register16, byte>(address, page);
return address;
}
private Register16 Address_IndexedIndirectX() => this.GetWordPaged(0, this.Address_ZeroPageX());
private Tuple<Register16, byte> Address_IndirectIndexedY()
private Register16 Address_IndirectIndexedY()
{
var address = this.Address_ZeroPageIndirect();
var page = address.High;
this.crossedPage = address.High;
address.Word += this.Y;
return new Tuple<Register16, byte>(address, page);
return address;
}
private ushort Address_relative_byte()
@ -668,11 +669,9 @@ namespace EightBit
private byte AM_AbsoluteX(PageCrossingBehavior behaviour = PageCrossingBehavior.MaybeReadTwice)
{
var crossed = this.Address_AbsoluteX();
var address = crossed.Item1;
var page = crossed.Item2;
var possible = this.BusRead(address.Low, page);
if ((behaviour == PageCrossingBehavior.AlwaysReadTwice) || (page != address.High))
var address = this.Address_AbsoluteX();
var possible = this.BusRead(address.Low, this.crossedPage);
if ((behaviour == PageCrossingBehavior.AlwaysReadTwice) || (this.crossedPage != address.High))
{
possible = this.BusRead(address.Word);
}
@ -682,11 +681,9 @@ namespace EightBit
private byte AM_AbsoluteY()
{
var crossed = this.Address_AbsoluteY();
var address = crossed.Item1;
var page = crossed.Item2;
var possible = this.BusRead(address.Low, page);
if (page != address.High)
var address = this.Address_AbsoluteY();
var possible = this.BusRead(address.Low, this.crossedPage);
if (this.crossedPage != address.High)
{
possible = this.BusRead(address.Word);
}
@ -702,11 +699,9 @@ namespace EightBit
private byte AM_IndirectIndexedY()
{
var crossed = this.Address_IndirectIndexedY();
var address = crossed.Item1;
var page = crossed.Item2;
var possible = this.BusRead(address.Low, page);
if (page != address.High)
var address = this.Address_IndirectIndexedY();
var possible = this.BusRead(address.Low, this.crossedPage);
if (this.crossedPage != address.High)
{
possible = this.BusRead(address);
}
@ -982,19 +977,15 @@ namespace EightBit
private void STA_AbsoluteX()
{
var crossed = this.Address_AbsoluteX();
var address = crossed.Item1;
var page = crossed.Item2;
this.BusRead(address.Low, page);
var address = this.Address_AbsoluteX();
this.BusRead(address.Low, this.crossedPage);
this.BusWrite(address, this.A);
}
private void STA_AbsoluteY()
{
var crossed = this.Address_AbsoluteY();
var address = crossed.Item1;
var page = crossed.Item2;
this.BusRead(address.Low, page);
var address = this.Address_AbsoluteY();
this.BusRead(address.Low, this.crossedPage);
this.BusWrite(address, this.A);
}
}