diff options
| author | Ian C <ianc@noddybox.co.uk> | 2011-12-31 00:10:45 +0000 |
|---|---|---|
| committer | Ian C <ianc@noddybox.co.uk> | 2011-12-31 00:10:45 +0000 |
| commit | 4a14a990665f766e349b9027dbf980bc39f395f6 (patch) | |
| tree | ba44e3f58e4792d5e496744a8f3651d5b30b3121 /Noddybox.Emulation.EightBit/Register16.cs | |
| parent | f96332b0913a8a365db73a1af3443c0e225a23d8 (diff) | |
Development check-in.
Diffstat (limited to 'Noddybox.Emulation.EightBit/Register16.cs')
| -rw-r--r-- | Noddybox.Emulation.EightBit/Register16.cs | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/Noddybox.Emulation.EightBit/Register16.cs b/Noddybox.Emulation.EightBit/Register16.cs new file mode 100644 index 0000000..06c9c01 --- /dev/null +++ b/Noddybox.Emulation.EightBit/Register16.cs @@ -0,0 +1,88 @@ +//
+// Copyright (c) 2012 Ian Cowburn
+//
+using System;
+using System.Runtime.InteropServices;
+
+namespace Noddybox.Emulation.EightBit
+{
+ /// <summary>
+ /// Provides a common 8-bit register pattern, which is two 8-bit registers rolled into one.
+ /// While this could be done at runtime using <see cref="BitConverter.IsLittleEndian"/> this
+ /// method was chosen for speed reasons; interfaces cannot define fields, which is sensible
+ /// enoough, but accessing fields directly would allow ref variables to be used with this type's
+ /// fields.
+ /// </summary>
+ [StructLayout(LayoutKind.Explicit)]
+ public struct Register16
+ {
+#if TARGET_IS_BIGENDIAN
+
+ /// <summary>
+ /// The 16-bit register.
+ /// </summary>
+ [FieldOffset(0)]
+ public ushort reg;
+
+ /// <summary>
+ /// The high 8-bits of the register.
+ /// </summary>
+ [FieldOffset(0)]
+ public byte high;
+
+ /// <summary>
+ /// The low 8-bits of the register.
+ /// </summary>
+ [FieldOffset(1)]
+ public byte low;
+
+#else
+
+ /// <summary>
+ /// The 16-bit register.
+ /// </summary>
+ [FieldOffset(0)]
+ public ushort reg;
+
+ /// <summary>
+ /// The low 8-bits of the register.
+ /// </summary>
+ [FieldOffset(0)]
+ public byte low;
+
+ /// <summary>
+ /// The high 8-bits of the register.
+ /// </summary>
+ [FieldOffset(1)]
+ public byte high;
+
+#endif
+
+ /// <summary>
+ /// Public constructor. This is provided to stop the compiler complaining when you use the struct as it
+ /// doesn't realise that setting <see cref="reg"/> will also set <see cref="low"/> and <see cref="high"/>.
+ /// </summary>
+ /// <param name="val">The 16-bit value to assign.</param>
+ public Register16(ushort val)
+ {
+ high = 0;
+ low = 0;
+ reg = val;
+ }
+
+ /// <summary>
+ /// Used to verify the compile-time setting at runtime.
+ /// </summary>
+ public static void Verify()
+ {
+ Register16 r = new Register16(0);
+
+ r.reg = 0x1234;
+
+ if (r.low != 0x24 || r.high != 0x12)
+ {
+ throw new Exception("Compile time endian setting incorrect");
+ }
+ }
+ }
+}
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