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feat(cpu): implement fix for ADC and implement SBC

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-01-18 14:16:58 -04:00
parent faa8f724a0
commit ae69d9981e
1 changed files with 15 additions and 2 deletions
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17
src/cpu/arm/data_processing.zig
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@ -10,6 +10,7 @@ pub fn dataProcessing(comptime I: bool, comptime S: bool, comptime instrKind: u4
fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u32) void { fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u32) void {
const rd = opcode >> 12 & 0xF; const rd = opcode >> 12 & 0xF;
const rn = opcode >> 16 & 0xF; const rn = opcode >> 16 & 0xF;
const old_carry = @boolToInt(cpu.cpsr.c.read());
const op1 = if (rn == 0xF) cpu.fakePC() else cpu.r[rn]; const op1 = if (rn == 0xF) cpu.fakePC() else cpu.r[rn];
@ -49,11 +50,10 @@ pub fn dataProcessing(comptime I: bool, comptime S: bool, comptime instrKind: u4
}, },
0x5 => { 0x5 => {
// ADC // ADC
const carry = @boolToInt(cpu.cpsr.c.read());
var result: u32 = undefined; var result: u32 = undefined;
const did = @addWithOverflow(u32, op1, op2, &result); const did = @addWithOverflow(u32, op1, op2, &result);
const overflow = @addWithOverflow(u32, result, carry, &result); const overflow = @addWithOverflow(u32, result, old_carry, &result);
cpu.r[rd] = result; cpu.r[rd] = result;
if (S and rd != 0xF) { if (S and rd != 0xF) {
@ -63,6 +63,19 @@ pub fn dataProcessing(comptime I: bool, comptime S: bool, comptime instrKind: u4
cpu.cpsr.v.write(((op1 ^ result) & (op2 ^ result)) >> 31 & 1 == 1); cpu.cpsr.v.write(((op1 ^ result) & (op2 ^ result)) >> 31 & 1 == 1);
} }
}, },
0x6 => {
// SBC
const subtrahend = @as(u64, op2) - old_carry + 1;
const result = @truncate(u32, op1 -% subtrahend);
cpu.r[rd] = result;
if (S and rd != 0xF) {
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(subtrahend <= op1);
cpu.cpsr.v.write(((op1 ^ result) & (~op2 ^ result)) >> 31 & 1 == 1);
}
},
0x8 => { 0x8 => {
// TST // TST
const result = op1 & op2; const result = op1 & op2;