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// Copyright 2024 Gabriel Bjørnager Jensen.
//
// This file is part of Pollex.
//
// Pollex is free software: you can redistribute it
// and/or modify it under the terms of the GNU Af-
// fero General Public License as published by the
// Free Software Foundation, either version 3 of
// the License, or (at your option) any later ver-
// sion.
//
// Pollex is distributed in the hope that it will
// be useful, but WITHOUT ANY WARRANTY; without
// even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Affero General Public License for more details.
//
// You should have received a copy of the GNU Af-
// fero General Public License along with Pollex.
// If not, see <https://www.gnu.org/licenses/>.
use core::fmt::Display;
use core::mem::transmute;
/// An instruction predicate (condition code).
///
/// Most Arm32 opcodes embed a condition code, as well as some Thumb opcodes.
///
/// Any 4-bit values is always a valid predicate *except* `0b1111`, which sometimes denotes a different instruction altogether
/// In most cases, it is invalid, however..
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
#[repr(u8)]
pub enum Predicate {
Equal = 0b0000,
NotEqual = 0b0001,
HigherOrSame = 0b0010,
Lower = 0b0011,
Minus = 0b0100,
Plus = 0b0101,
Overflow = 0b0110,
NoOverflow = 0b0111,
Higher = 0b1000,
LowerOrSame = 0b1001,
GreaterThanOrEqual = 0b1010,
LessThan = 0b1011,
GreaterThan = 0b1100,
LessThanOrEqual = 0b1101,
Always = 0b1110,
//Never = 0b1111,
}
impl Predicate {
/// Converts the provided byte into a register identifier.
/// If the byte's value is not a valid predicate, [`None`] is returned.
///
/// This conversion is valid for all values less than or equal (14).
#[inline]
#[must_use]
pub const fn from_u8(value: u8) -> Option<Self> {
if value <= 0b1110 {
Some(unsafe { transmute::<u8, Self>(value) })
} else {
None
}
}
}
impl Display for Predicate {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
use Predicate::*;
match *self {
Equal => write!(f, "EQ"),
NotEqual => write!(f, "NE"),
HigherOrSame => write!(f, "HS"),
Lower => write!(f, "LO"),
Minus => write!(f, "MI"),
Plus => write!(f, "PL"),
Overflow => write!(f, "VS"),
NoOverflow => write!(f, "VC"),
Higher => write!(f, "HI"),
LowerOrSame => write!(f, "LS"),
GreaterThanOrEqual => write!(f, "GE"),
LessThan => write!(f, "LT"),
GreaterThan => write!(f, "GT"),
LessThanOrEqual => write!(f, "LE"),
Always => Ok(()), // No need to print this one.
//Never => write!(f, "NV"),
}
}
}
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