58 lines
2.2 KiB
Zig
58 lines
2.2 KiB
Zig
const Bus = @import("../../Bus.zig");
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const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
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const InstrFn = @import("../../cpu.zig").arm.InstrFn;
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pub fn multiply(comptime A: bool, comptime S: bool) 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 = opcode >> 16 & 0xF;
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const rn = opcode >> 12 & 0xF;
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const rs = opcode >> 8 & 0xF;
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const rm = opcode & 0xF;
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const temp: u64 = @as(u64, cpu.r[rm]) * @as(u64, cpu.r[rs]) + if (A) cpu.r[rn] else 0;
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const result = @truncate(u32, temp);
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cpu.r[rd] = result;
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if (S) {
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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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// V is unaffected, C is *actually* undefined in ARMv4
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}
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}
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}.inner;
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}
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pub fn multiplyLong(comptime U: bool, comptime A: bool, comptime S: bool) 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_hi = opcode >> 16 & 0xF;
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const rd_lo = opcode >> 12 & 0xF;
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const rs = opcode >> 8 & 0xF;
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const rm = opcode & 0xF;
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if (U) {
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// Signed (WHY IS IT U THEN?)
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var result: i64 = @as(i64, @bitCast(i32, cpu.r[rm])) * @as(i64, @bitCast(i32, cpu.r[rs]));
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if (A) result +%= @bitCast(i64, @as(u64, cpu.r[rd_hi]) << 32 | @as(u64, cpu.r[rd_lo]));
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cpu.r[rd_hi] = @bitCast(u32, @truncate(i32, result >> 32));
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cpu.r[rd_lo] = @bitCast(u32, @truncate(i32, result));
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} else {
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// Unsigned
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var result: u64 = @as(u64, cpu.r[rm]) * @as(u64, cpu.r[rs]);
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if (A) result +%= @as(u64, cpu.r[rd_hi]) << 32 | @as(u64, cpu.r[rd_lo]);
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cpu.r[rd_hi] = @truncate(u32, result >> 32);
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cpu.r[rd_lo] = @truncate(u32, result);
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}
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if (S) {
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cpu.cpsr.z.write(cpu.r[rd_hi] == 0 and cpu.r[rd_lo] == 0);
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cpu.cpsr.n.write(cpu.r[rd_hi] >> 31 & 1 == 1);
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// C and V are set to meaningless values
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}
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}
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}.inner;
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}
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