zba/src/cpu/arm/data_processing.zig

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const std = @import("std");
const shifter = @import("barrel_shifter.zig");
const Bus = @import("../../Bus.zig");
const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
const InstrFn = @import("../../cpu.zig").ArmInstrFn;
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pub fn dataProcessing(comptime I: bool, comptime S: bool, comptime instrKind: u4) InstrFn {
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return struct {
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fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u32) void {
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const rd = @truncate(u4, opcode >> 12 & 0xF);
const rn = opcode >> 16 & 0xF;
const old_carry = @boolToInt(cpu.cpsr.c.read());
// If certain conditions are met, PC is 12 ahead instead of 8
if (!I and opcode >> 4 & 1 == 1) cpu.r[15] += 4;
const op1 = if (rn == 0xF) cpu.fakePC() else cpu.r[rn];
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var op2: u32 = undefined;
if (I) {
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const amount = @truncate(u8, (opcode >> 8 & 0xF) << 1);
op2 = shifter.rotateRight(S, &cpu.cpsr, opcode & 0xFF, amount);
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} else {
op2 = shifter.execute(S, cpu, opcode);
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}
// Undo special condition from above
if (!I and opcode >> 4 & 1 == 1) cpu.r[15] -= 4;
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switch (instrKind) {
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0x0 => {
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// AND
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const result = op1 & op2;
cpu.r[rd] = result;
logicFlags(S, cpu, rd, result);
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},
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0x1 => {
// EOR
const result = op1 ^ op2;
cpu.r[rd] = result;
logicFlags(S, cpu, rd, result);
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},
0x2 => cpu.r[rd] = sub(S, cpu, rd, op1, op2), // SUB
0x3 => cpu.r[rd] = sub(S, cpu, rd, op2, op1), // RSB
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0x4 => {
// ADD
var result: u32 = undefined;
const didOverflow = @addWithOverflow(u32, op1, op2, &result);
cpu.r[rd] = result;
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if (S) {
if (rd == 0xF) {
cpu.setCpsr(cpu.spsr.raw);
} else {
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(didOverflow);
cpu.cpsr.v.write(((op1 ^ result) & (op2 ^ result)) >> 31 & 1 == 1);
}
}
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},
0x5 => {
// ADC
var result: u32 = undefined;
const did = @addWithOverflow(u32, op1, op2, &result);
const overflow = @addWithOverflow(u32, result, old_carry, &result);
cpu.r[rd] = result;
if (S) {
if (rd == 0xF) {
cpu.setCpsr(cpu.spsr.raw);
} else {
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(did or overflow);
cpu.cpsr.v.write(((op1 ^ result) & (op2 ^ result)) >> 31 & 1 == 1);
}
}
},
0x6 => cpu.r[rd] = sbc(S, cpu, rd, op1, op2, old_carry), // SBC
0x7 => cpu.r[rd] = sbc(S, cpu, rd, op2, op1, old_carry), // RSC
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0x8 => {
// TST
const result = op1 & op2;
testFlags(S, cpu, opcode, result);
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},
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0x9 => {
// TEQ
const result = op1 ^ op2;
testFlags(S, cpu, opcode, result);
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},
0xA => {
// CMP
const result = op1 -% op2;
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cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(op2 <= op1);
cpu.cpsr.v.write(((op1 ^ result) & (~op2 ^ result)) >> 31 & 1 == 1);
},
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0xB => {
// CMN
var result: u32 = undefined;
const didOverflow = @addWithOverflow(u32, op1, op2, &result);
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(didOverflow);
cpu.cpsr.v.write(((op1 ^ result) & (op2 ^ result)) >> 31 & 1 == 1);
},
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0xC => {
// ORR
const result = op1 | op2;
cpu.r[rd] = result;
logicFlags(S, cpu, rd, result);
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},
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0xD => {
// MOV
cpu.r[rd] = op2;
logicFlags(S, cpu, rd, op2);
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},
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0xE => {
// BIC
const result = op1 & ~op2;
cpu.r[rd] = result;
logicFlags(S, cpu, rd, result);
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},
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0xF => {
// MVN
const result = ~op2;
cpu.r[rd] = result;
logicFlags(S, cpu, rd, result);
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},
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}
}
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}.inner;
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}
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fn sbc(comptime S: bool, cpu: *Arm7tdmi, rd: u4, left: u32, right: u32, old_carry: u1) u32 {
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// TODO: Make your own version (thanks peach.bot)
const subtrahend = @as(u64, right) - old_carry + 1;
const result = @truncate(u32, left -% subtrahend);
if (S) {
if (rd == 0xF) {
cpu.setCpsr(cpu.spsr.raw);
} else {
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(subtrahend <= left);
cpu.cpsr.v.write(((left ^ result) & (~right ^ result)) >> 31 & 1 == 1);
}
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}
return result;
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}
fn sub(comptime S: bool, cpu: *Arm7tdmi, rd: u4, left: u32, right: u32) u32 {
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const result = left -% right;
if (S) {
if (rd == 0xF) {
cpu.setCpsr(cpu.spsr.raw);
} else {
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
cpu.cpsr.c.write(right <= left);
cpu.cpsr.v.write(((left ^ result) & (~right ^ result)) >> 31 & 1 == 1);
}
}
return result;
}
fn logicFlags(comptime S: bool, cpu: *Arm7tdmi, rd: u4, result: u32) void {
if (S) {
if (rd == 0xF) {
cpu.setCpsr(cpu.spsr.raw);
} else {
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
// C set by Barrel Shifter, V is unaffected
}
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}
}
fn testFlags(comptime S: bool, cpu: *Arm7tdmi, opcode: u32, result: u32) void {
cpu.cpsr.n.write(result >> 31 & 1 == 1);
cpu.cpsr.z.write(result == 0);
// Barrel Shifter should always calc CPSR C in TST
if (!S) _ = shifter.execute(true, cpu, opcode);
}