58 lines
2.0 KiB
Zig
58 lines
2.0 KiB
Zig
const std = @import("std");
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const Bus = @import("../../Bus.zig");
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const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
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const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
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pub fn format3(comptime op: u2, comptime rd: u3) InstrFn {
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return struct {
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fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u16) void {
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const offset = @truncate(u8, opcode);
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switch (op) {
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0b00 => {
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// MOV
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cpu.r[rd] = offset;
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cpu.cpsr.n.unset();
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cpu.cpsr.z.write(offset == 0);
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},
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0b01 => {
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// CMP
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const left = cpu.r[rd];
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const result = left -% offset;
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cpu.cpsr.n.write(result >> 31 & 1 == 1);
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cpu.cpsr.z.write(result == 0);
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cpu.cpsr.c.write(offset <= left);
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cpu.cpsr.v.write(((left ^ result) & (~offset ^ result)) >> 31 & 1 == 1);
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},
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0b10 => {
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// ADD
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const left = cpu.r[rd];
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var result: u32 = undefined;
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const didOverflow = @addWithOverflow(u32, left, offset, &result);
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cpu.r[rd] = result;
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cpu.cpsr.n.write(result >> 31 & 1 == 1);
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cpu.cpsr.z.write(result == 0);
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cpu.cpsr.c.write(didOverflow);
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cpu.cpsr.v.write(((left ^ result) & (offset ^ result)) >> 31 & 1 == 1);
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},
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0b11 => {
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// SUB
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const left = cpu.r[rd];
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const result = left -% offset;
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cpu.r[rd] = result;
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cpu.cpsr.n.write(result >> 31 & 1 == 1);
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cpu.cpsr.z.write(result == 0);
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cpu.cpsr.c.write(offset <= left);
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cpu.cpsr.v.write(((left ^ result) & (~offset ^ result)) >> 31 & 1 == 1);
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},
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}
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}
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}.inner;
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}
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