paoda/zba
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

chore(cpu): refactor barrel shifter

Browse Source
This commit is contained in:
Rekai Nyangadzayi Musuka
2022-01-17 11:17:04 -04:00
parent d05a924420
commit 1025500407
3 changed files with 31 additions and 55 deletions
Download Patch File Download Diff File Expand all files Collapse all files

58
src/cpu/arm/barrel_shifter.zig
View File

@@ -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);
}