Hello, I’m writing a gameboy emulator to learn zig and ran into a compile error I cannot figure out. I’m implementing an instruction to add or subtract binary coded decimals and need to check some flags and also the value of the register.
The error is
src\cpu.zig:189:35: error: unable to evaluate comptime expression
if ((flags.subtract and a & 0xF > 0x09) || flags.half_carry) {
I’ve also tried chaning it to
if (flags.subtract || flags.half_carry)
but got the same error on the flag.subtract. The full code for this is below, thank you in advance for any help.
pub const Flags = struct {
zero: bool, // Z flag
subtract: bool, // N flag
half_carry: bool, // H flag
carry: bool, // C flag
pub fn set(self: *Flags, zero: bool, subtract: bool, half_carry: bool, carry: bool) void {
self.zero = zero;
self.subtract = subtract;
self.half_carry = half_carry;
self.carry = carry;
}
};
fn daa(self: *CPU) struct { u8, bool } {
var offset: u8 = 0;
var should_carry = false;
const a = self.registers.a;
const flags = self.flags;
// Compile error is on the line under this
if ((flags.subtract and a & 0xF > 0x09) || flags.half_carry) {
offset |= 0x06;
}
if ((flags.subtract and a > 0x99) || self.flags.carry) {
offset |= 0x60;
should_carry = true;
}
return .{ if (flags.subtract) @subWithOverflow(a, offset)[0] else @addWithOverflow(a, offset)[0], should_carry };
}