zba/lib/bitfield.zig

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const std = @import("std");
fn PtrCastPreserveCV(comptime T: type, comptime PtrToT: type, comptime NewT: type) type {
return switch (PtrToT) {
*T => *NewT,
*const T => *const NewT,
*volatile T => *volatile NewT,
*const volatile T => *const volatile NewT,
else => @compileError("wtf you doing"),
};
}
fn BitType(comptime FieldType: type, comptime ValueType: type, comptime shamt: usize) type {
const self_bit: FieldType = (1 << shamt);
return extern struct {
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bits: Bitfield(FieldType, shamt, 1),
pub fn set(self: anytype) void {
self.bits.field().* |= self_bit;
}
pub fn unset(self: anytype) void {
self.bits.field().* &= ~self_bit;
}
pub fn read(self: anytype) ValueType {
return @bitCast(ValueType, @truncate(u1, self.bits.field().* >> shamt));
}
// Since these are mostly used with MMIO, I want to avoid
// reading the memory just to write it again, also races
pub fn write(self: anytype, val: ValueType) void {
if (@bitCast(bool, val)) {
self.set();
} else {
self.unset();
}
}
};
}
// Original Bit Constructor
// pub fn Bit(comptime FieldType: type, comptime shamt: usize) type {
// return BitType(FieldType, u1, shamt);
// }
pub fn Bit(comptime FieldType: type, comptime shamt: usize) type {
return BitType(FieldType, bool, shamt);
}
fn Boolean(comptime FieldType: type, comptime shamt: usize) type {
return BitType(FieldType, bool, shamt);
}
pub fn Bitfield(comptime FieldType: type, comptime shamt: usize, comptime num_bits: usize) type {
if (shamt + num_bits > @bitSizeOf(FieldType)) {
@compileError("bitfield doesn't fit");
}
const self_mask: FieldType = ((1 << num_bits) - 1) << shamt;
const ValueType = std.meta.Int(.unsigned, num_bits);
return extern struct {
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dummy: FieldType,
fn field(self: anytype) PtrCastPreserveCV(@This(), @TypeOf(self), FieldType) {
return @ptrCast(PtrCastPreserveCV(@This(), @TypeOf(self), FieldType), self);
}
pub fn write(self: anytype, val: ValueType) void {
self.field().* &= ~self_mask;
self.field().* |= @intCast(FieldType, val) << shamt;
}
pub fn read(self: anytype) ValueType {
const val: FieldType = self.field().*;
return @intCast(ValueType, (val & self_mask) >> shamt);
}
};
}
test "bit" {
const S = extern union {
low: Bit(u32, 0),
high: Bit(u32, 1),
val: u32,
};
std.testing.expect(@sizeOf(S) == 4);
std.testing.expect(@bitSizeOf(S) == 32);
var s: S = .{ .val = 1 };
std.testing.expect(s.low.read() == 1);
std.testing.expect(s.high.read() == 0);
s.low.write(0);
s.high.write(1);
std.testing.expect(s.val == 2);
}
test "boolean" {
const S = extern union {
low: Boolean(u32, 0),
high: Boolean(u32, 1),
val: u32,
};
std.testing.expect(@sizeOf(S) == 4);
std.testing.expect(@bitSizeOf(S) == 32);
var s: S = .{ .val = 2 };
std.testing.expect(s.low.read() == false);
std.testing.expect(s.high.read() == true);
s.low.write(true);
s.high.write(false);
std.testing.expect(s.val == 1);
}
test "bitfield" {
const S = extern union {
low: Bitfield(u32, 0, 16),
high: Bitfield(u32, 16, 16),
val: u32,
};
std.testing.expect(@sizeOf(S) == 4);
std.testing.expect(@bitSizeOf(S) == 32);
var s: S = .{ .val = 0x13376969 };
std.testing.expect(s.low.read() == 0x6969);
std.testing.expect(s.high.read() == 0x1337);
s.low.write(0x1337);
s.high.write(0x6969);
std.testing.expect(s.val == 0x69691337);
}