private static BeImageReader?GetA5InitImageReader(ImageSegment a5dataSegment)
{
var a5data = a5dataSegment.MemoryArea;
var a5dr = new BeImageReader((ByteMemoryArea)a5data, 0);
if (!a5dr.TryReadBeUInt32(out uint a5d0))
{
return(null);
}
if (!a5dr.TryReadBeUInt16(out ushort a5d1))
{
return(null);
}
var a5dheaderOffset = a5dr.ReadBeUInt16();
const uint A5Init_Sig_Movem_l = 0x48E77FF8; // movem.l\td1-d7/a0-a4,-(a7)
const ushort A5Init_Sig_Lea = 0x49FA; // First word of lea\t$????(pc),a4 instruction
if (a5d0 != A5Init_Sig_Movem_l || a5d1 != A5Init_Sig_Lea || a5dheaderOffset >= a5dataSegment.MemoryArea.Length)
{
// Starting code bytes incorrect or
// Invalid offset to compressed global data - outside of A5World memory segment.
// No global compressed data
return(null);
}
a5dr.Seek(a5dheaderOffset - 2);
return(a5dr);
}
public void Relocate()
{
var memA5 = (ByteMemoryArea)platform.A5World.MemoryArea;
var a5belowWriter = new BeImageWriter(memA5, 0);
var a5belowReader = new BeImageReader(memA5, 0);
uint a5globalOffset = platform.A5Offset - a5dbelow;
var a5WorldAddress = (UInt32)((platform.A5World.Address.Offset + platform.A5Offset) & 0xFFFFFFFF);
// set Repeat count = 1, reset after each completed copy cycle
// byte token lower 4 bits number of words to copy from compressed data
// byte token upper 4 bits number of words to skip in global application data space
// if either value is 0 then get run length value which is in bytes.
// if the new run length value for copy is 0 then it's the end of compression data.
for (;;)
{
int a5repeat = 1;
// Skip is number of 16-bit words to skip
uint a5globalSkip = a5dr.ReadByte();
if (a5globalSkip == 0)
{
a5globalSkip = a5dr.ReadByte();
if (a5globalSkip == 0)
{
break;
}
if (a5globalSkip > 0x7F)
{
a5globalSkip = ((a5globalSkip & 0x7F) << 8) + a5dr.ReadByte();
a5globalSkip = (a5globalSkip << 16) + a5dr.ReadBeUInt16();
}
else
{
a5repeat = ResourceFork.GetRunLengthValue(a5dr, ref a5repeat);
//$BUG: a5repeat could return the value 0. The do-while below will
// decrement a5repeat before testing. This will lead to an effective
// repeat count of 2^32; likely not wanted.
}
}
else
{
if ((a5globalSkip & 0x80) == 0x80)
{
a5globalSkip = ((a5globalSkip & 0x7F) << 8) + a5dr.ReadByte();
}
}
a5globalSkip = a5globalSkip * 2;
do
{
a5globalOffset += a5globalSkip;
a5belowReader.Seek(a5globalOffset, SeekOrigin.Begin);
uint a5ptrOffset = a5belowReader.ReadBeUInt32();
a5belowWriter.Position = (int)a5globalOffset;
// write relocated A5World pointers to absolute address in A5World segment
// Possible register/mark as Global pointer references to strings
a5belowWriter.WriteBeUInt32((a5WorldAddress + a5ptrOffset) & 0xFFFFFFFF);
--a5repeat;
} while (a5repeat > 0);
}
}