From 41bab3d6ba462e212fcda61fce86fce4f54940e9 Mon Sep 17 00:00:00 2001 From: Rekai Musuka Date: Fri, 21 Oct 2022 05:11:58 -0300 Subject: [PATCH] chore(cpu): refactor barrel shifter --- src/cpu/arm/barrel_shifter.zig | 58 ++++++++++++---------------- src/cpu/arm/data_processing.zig | 14 +------ src/cpu/arm/single_data_transfer.zig | 14 +++---- 3 files changed, 31 insertions(+), 55 deletions(-) diff --git a/src/cpu/arm/barrel_shifter.zig b/src/cpu/arm/barrel_shifter.zig index 29eee16..a7f28d4 100644 --- a/src/cpu/arm/barrel_shifter.zig +++ b/src/cpu/arm/barrel_shifter.zig @@ -19,83 +19,73 @@ pub fn exec(comptime S: bool, cpu: *Arm7tdmi, opcode: u32) u32 { value = cpu.r[opcode & 0xF]; } - if (S) { - return switch (@truncate(u2, opcode >> 5)) { - 0b00 => logicalLeft(&cpu.cpsr, value, shift_amt), - 0b01 => logicalRight(&cpu.cpsr, value, shift_amt), - 0b10 => arithmetic_right(&cpu.cpsr, value, shift_amt), - 0b11 => rotateRight(&cpu.cpsr, value, shift_amt), - }; - } else { - var dummy = CPSR{ .raw = 0x0000_0000 }; - return switch (@truncate(u2, opcode >> 5)) { - 0b00 => logicalLeft(&dummy, value, shift_amt), - 0b01 => logicalRight(&dummy, value, shift_amt), - 0b10 => arithmetic_right(&dummy, value, shift_amt), - 0b11 => rotateRight(&dummy, value, shift_amt), - }; - } + return switch (@truncate(u2, opcode >> 5)) { + 0b00 => logicalLeft(S, &cpu.cpsr, value, shift_amt), + 0b01 => logicalRight(S, &cpu.cpsr, value, shift_amt), + 0b10 => arithmeticRight(S, &cpu.cpsr, value, shift_amt), + 0b11 => rotateRight(S, &cpu.cpsr, value, shift_amt), + }; } -pub fn logicalLeft(cpsr: *CPSR, rm: u32, shift_byte: u8) u32 { - const shift_amt = @truncate(u5, shift_byte); +pub fn logicalLeft(comptime S: bool, cpsr: *CPSR, rm: u32, amount: u8) u32 { + const shift_amt = @truncate(u5, amount); const bit_count: u8 = @typeInfo(u32).Int.bits; var result: u32 = 0x0000_0000; - if (shift_byte < bit_count) { + if (amount < bit_count) { // We can perform a well-defined shift here // FIXME: We assume cpu.r[rs] == 0 and imm_shift == 0 are equivalent - if (shift_amt != 0) { + if (S and shift_amt != 0) { const carry_bit = @truncate(u5, bit_count - shift_amt); cpsr.c.write(rm >> carry_bit & 1 == 1); } result = rm << shift_amt; - } else if (shift_byte == bit_count) { + } else if (amount == bit_count) { // Shifted all bits out, carry bit is bit 0 of rm - cpsr.c.write(rm & 1 == 1); + if (S) cpsr.c.write(rm & 1 == 1); } else { // Shifted all bits out, carry bit has also been shifted out - cpsr.c.write(false); + if (S) cpsr.c.write(false); } return result; } -pub fn logicalRight(cpsr: *CPSR, rm: u32, shift_byte: u8) u32 { - const shift_amt = @truncate(u5, shift_byte); +pub fn logicalRight(comptime S: bool, cpsr: *CPSR, rm: u32, amount: u32) u32 { + const shift_amt = @truncate(u5, amount); const bit_count: u8 = @typeInfo(u32).Int.bits; var result: u32 = 0x0000_0000; - if (shift_byte == 0 or shift_byte == bit_count) { + if (amount == 0 or amount == bit_count) { // Actualy LSR #32 - cpsr.c.write(rm >> 31 & 1 == 1); - } else if (shift_byte < bit_count) { + if (S) cpsr.c.write(rm >> 31 & 1 == 1); + } else if (amount < bit_count) { // We can perform a well-defined shift const carry_bit = shift_amt - 1; - cpsr.c.write(rm >> carry_bit & 1 == 1); + if (S) cpsr.c.write(rm >> carry_bit & 1 == 1); result = rm >> shift_amt; } else { // All bits have been shifted out, including carry bit - cpsr.c.write(false); + if (S) cpsr.c.write(false); } return result; } -pub fn arithmetic_right(_: *CPSR, _: u32, _: u8) u32 { +pub fn arithmeticRight(comptime _: bool, _: *CPSR, _: u32, _: u8) u32 { // @bitCast(u32, @bitCast(i32, r_val) >> @truncate(u5, amount)) std.debug.panic("[BarrelShifter] implement arithmetic shift right", .{}); } -pub fn rotateRight(cpsr: *CPSR, rm: u32, shift_byte: u8) u32 { - const result = std.math.rotr(u32, rm, shift_byte); +pub fn rotateRight(comptime S: bool, cpsr: *CPSR, rm: u32, amount: u8) u32 { + const result = std.math.rotr(u32, rm, amount); - if (result != 0) { + if (S and result != 0) { cpsr.c.write(result >> 31 & 1 == 1); } diff --git a/src/cpu/arm/data_processing.zig b/src/cpu/arm/data_processing.zig index f94db67..b7c214a 100644 --- a/src/cpu/arm/data_processing.zig +++ b/src/cpu/arm/data_processing.zig @@ -22,18 +22,8 @@ pub fn dataProcessing(comptime I: bool, comptime S: bool, comptime instrKind: u4 var op2: u32 = undefined; if (I) { - const amt = @truncate(u8, (opcode >> 8 & 0xF) << 1); - - if (S) { - op2 = BarrelShifter.rotateRight(&cpu.cpsr, opcode & 0xFF, amt); - } else { - const PSR = @import("../../cpu.zig").PSR; - var dummy = PSR{ .raw = 0x0000_0000 }; - - op2 = BarrelShifter.rotateRight(&dummy, opcode & 0xFF, amt); - } - - // op2 = std.math.rotr(u32, opcode & 0xFF, (opcode >> 8 & 0xF) << 1); + const amount = @truncate(u8, (opcode >> 8 & 0xF) << 1); + op2 = BarrelShifter.rotateRight(S, &cpu.cpsr, opcode & 0xFF, amount); } else { op2 = BarrelShifter.exec(S, cpu, opcode); } diff --git a/src/cpu/arm/single_data_transfer.zig b/src/cpu/arm/single_data_transfer.zig index 4b9bcb2..3fabd6d 100644 --- a/src/cpu/arm/single_data_transfer.zig +++ b/src/cpu/arm/single_data_transfer.zig @@ -4,7 +4,6 @@ const util = @import("../../util.zig"); const BarrelShifter = @import("barrel_shifter.zig"); const Bus = @import("../../Bus.zig"); const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi; -const CPSR = @import("../../cpu.zig").PSR; const InstrFn = @import("../../cpu.zig").ArmInstrFn; pub fn singleDataTransfer(comptime I: bool, comptime P: bool, comptime U: bool, comptime B: bool, comptime W: bool, comptime L: bool) InstrFn { @@ -55,16 +54,13 @@ pub fn singleDataTransfer(comptime I: bool, comptime P: bool, comptime U: bool, } fn registerOffset(cpu: *Arm7tdmi, opcode: u32) u32 { - const shift_byte = @truncate(u8, opcode >> 7 & 0x1F); - + const amount = @truncate(u8, opcode >> 7 & 0x1F); const rm = cpu.r[opcode & 0xF]; - var dummy = CPSR{ .raw = 0x0000_0000 }; - return switch (@truncate(u2, opcode >> 5)) { - 0b00 => BarrelShifter.logicalLeft(&dummy, rm, shift_byte), - 0b01 => BarrelShifter.logicalRight(&dummy, rm, shift_byte), - 0b10 => BarrelShifter.arithmetic_right(&dummy, rm, shift_byte), - 0b11 => BarrelShifter.rotateRight(&dummy, rm, shift_byte), + 0b00 => BarrelShifter.logicalLeft(false, &cpu.cpsr, rm, amount), + 0b01 => BarrelShifter.logicalRight(false, &cpu.cpsr, rm, amount), + 0b10 => BarrelShifter.arithmeticRight(false, &cpu.cpsr, rm, amount), + 0b11 => BarrelShifter.rotateRight(false, &cpu.cpsr, rm, amount), }; }