Mzxrules: /* Example C# Code */ pretty

2015-11-07T00:00:13Z

‎Example C# Code: pretty

Mzxrules: Created page with "The CRC is a special value used to verify the rom's data. == How it works == On system boot, the rom performs a calculation that I don't understand. It checks the state of 0x..."

2015-11-02T09:18:03Z

Created page with "The CRC is a special value used to verify the rom's data. == How it works == On system boot, the rom performs a calculation that I don't understand. It checks the state of 0x..."

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The CRC is a special value used to verify the rom's data.

== How it works ==
On system boot, the rom performs a calculation that I don't understand. It checks the state of 0x100000 bytes, starting at 0x1000 into the rom. Because of this, the CRC must be recalculated and written to the [[makerom]] header whenever the following files are modified:

{|class="wikitable"
! File
|-
| [[boot]]
|-
| [[dmadata]]
|-
| [[Audiobank]]
|-
| [[Audioseq]]
|-
| [[Audiotable]]
|}

== Example C# Code ==
<pre>public static void Write(Stream sw)
{
uint[] crc = new uint[2];
byte[] data = new byte[0x00101000];

uint d, r, t1, t2, t3, t4, t5, t6 = 0xDF26F436;

t1 = t2 = t3 = t4 = t5 = t6;

sw.Position = 0;
sw.Read(data, 0, 0x00101000);

for (int i = 0x00001000; i < 0x00101000; i += 4)
{
d = (uint)((data[i] << 24) | (data[i + 1] << 16) | (data[i + 2] << 8) | data[i + 3]);
if ((t6 + d) < t6) t4++;
t6 += d;
t3 ^= d;
r = (d << (int)(d & 0x1F)) | (d >> (32 - (int)(d & 0x1F)));
t5 += r;
if (t2 > d) t2 ^= r;
else t2 ^= t6 ^ d;
t1 += (uint)((data[0x00000750 + (i & 0xFF)] << 24) | (data[0x00000751 + (i & 0xFF)] << 16) |
(data[0x00000752 + (i & 0xFF)] << 8) | data[0x00000753 + (i & 0xFF)]) ^ d;
}
crc[0] = t6 ^ t4 ^ t3;
crc[1] = t5 ^ t2 ^ t1;

if (BitConverter.IsLittleEndian)
{
crc[0] = (crc[0] >> 24) | ((crc[0] >> 8) & 0xFF00) | ((crc[0] << 8) & 0xFF0000) | ((crc[0] << 24) & 0xFF000000);
crc[1] = (crc[1] >> 24) | ((crc[1] >> 8) & 0xFF00) | ((crc[1] << 8) & 0xFF0000) | ((crc[1] << 24) & 0xFF000000);
}

//Seek to 0x10 from rom start
sw.Position = 0x10;
BinaryWriter br = new BinaryWriter(sw);
br.Write(crc[0]);
br.Write(crc[1]);
}
</pre>
[[Category:Documentation]]

@@ Line 19: / Line 19: @@
 == Example C# Code ==
-<pre>public static void Write(Stream sw)
+{
      uint[] crc = new uint[2];
@@ Line 59: / Line 60: @@
      br.Write(crc[1]);
+}
-</pre>
+</syntaxhighlight>
 [[Category:Documentation]]

CRC - Revision history

Mzxrules: /* Example C# Code */ pretty

Mzxrules: Created page with "The CRC is a special value used to verify the rom's data. == How it works == On system boot, the rom performs a calculation that I don't understand. It checks the state of 0x..."