From 7fd114712c1921cb03748d42deeb655f6b225cce Mon Sep 17 00:00:00 2001
From: James Barnett <noreply@jamesbarnett.xyz>
Date: Tue, 17 Jul 2018 21:01:26 +0100
Subject: Implement the last set of ops. RETs

---
 src/main/kotlin/cpu/opcodes/Returns.kt | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 src/main/kotlin/cpu/opcodes/Returns.kt

(limited to 'src/main/kotlin/cpu/opcodes')

diff --git a/src/main/kotlin/cpu/opcodes/Returns.kt b/src/main/kotlin/cpu/opcodes/Returns.kt
new file mode 100644
index 0000000..b78e2d6
--- /dev/null
+++ b/src/main/kotlin/cpu/opcodes/Returns.kt
@@ -0,0 +1,28 @@
+package cpu.opcodes
+
+import cpu.Operation
+import cpu.Registers
+import ram.Ram
+import BitManipulation as bm
+
+val returns = mapOf(
+
+  0xC9 to Operation("RET", 0, 8, {r, m, _ -> ret(r, m)}),
+
+  0xC0 to Operation("RET NZ,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.ZERO) == 0) ret(r, m)}),
+  0xC8 to Operation("RET Z,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.ZERO) == 1) ret(r, m)}),
+  0xD0 to Operation("RET NC,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.CARRY) == 0) ret(r, m)}),
+  0xD8 to Operation("RET C,nn", 0, 8, {r, m, _ -> if(r.getFlag(Registers.Flag.CARRY) == 1) ret(r, m)}),
+
+  // TODO - enable interrupts once added
+  0xC9 to Operation("RET", 0, 8, {r, m, _ -> ret(r, m)})
+
+)
+
+private fun ret(r: Registers, m: Ram) {
+
+  val lsb = m.readByte(r.getAndIncrementSP())
+  val msb = m.readByte(r.getAndIncrementSP())
+
+  r.PC = bm.bytesToWord(msb, lsb)
+}
\ No newline at end of file
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