diff options
Diffstat (limited to 'src/main/kotlin/cpu/opcodes/Loads16Bit.kt')
| -rw-r--r-- | src/main/kotlin/cpu/opcodes/Loads16Bit.kt | 23 |
1 files changed, 22 insertions, 1 deletions
diff --git a/src/main/kotlin/cpu/opcodes/Loads16Bit.kt b/src/main/kotlin/cpu/opcodes/Loads16Bit.kt index 671a02d..830f6ab 100644 --- a/src/main/kotlin/cpu/opcodes/Loads16Bit.kt +++ b/src/main/kotlin/cpu/opcodes/Loads16Bit.kt @@ -2,6 +2,7 @@ package cpu.opcodes import cpu.Operation import cpu.Registers +import cpu.Registers.Flag import ram.Ram import BitManipulation as bm @@ -15,7 +16,27 @@ var loads16Bit = mapOf( 0xF9 to Operation("LD SP,HL", 0, 8, {r, _, _ -> r.SP = r.HL}), - 0xF8 to Operation("LDHL SP,n", 1, 12, {r, _, a -> r.HL = (r.SP + a[0])}), // TODO - not sure what the flags should be here + 0xF8 to Operation("LDHL SP,n", 1, 12, {r, _, a -> + + // https://stackoverflow.com/questions/5159603/gbz80-how-does-ld-hl-spe-affect-h-and-c-flags + // the carry flag is set if there's an overflow from the 7th to 8th bit. + // the half carry flag is set if there's an overflow from the 3rd into the 4th bit. + r.clearFlags() + + val absoluteValue = bm.getAbsoluteValue(a[0]) + + if (bm.isSignedBitNegative(a[0])) { + r.setFlagFromBool(Flag.HALF_CARRY, r.SP and 0x0F < absoluteValue and 0x0F) + r.setFlagFromBool(Flag.CARRY,r.SP and 0xFF < absoluteValue) + r.HL = r.SP - absoluteValue + + } else { + r.setFlagFromBool(Flag.HALF_CARRY,(r.SP and 0x0F) + (absoluteValue and 0x0F) > 0x0F) + r.setFlagFromBool(Flag.CARRY,(r.SP and 0xFF) + absoluteValue > 0xFF) + r.HL = r.SP + absoluteValue + } + + }), 0x08 to Operation("LD (nn),SP", 2, 20, {r, m, a -> m.writeByte(bm.argsToWord(a), bm.getLsb(r.SP)) m.writeByte(bm.argsToWord(a) + 1, bm.getMsb(r.SP)) |