diff options
Diffstat (limited to 'src/arm32/register')
| -rw-r--r-- | src/arm32/register/mod.rs | 35 |
1 files changed, 32 insertions, 3 deletions
diff --git a/src/arm32/register/mod.rs b/src/arm32/register/mod.rs index 0013c46..0c86093 100644 --- a/src/arm32/register/mod.rs +++ b/src/arm32/register/mod.rs @@ -19,16 +19,31 @@ // fero General Public License along with Pollex. // If not, see <https://www.gnu.org/licenses/>. +use alloc::borrow::ToOwned; + use crate::Error; use core::fmt::Display; +use core::mem::transmute; use core::str::FromStr; /// An Arm register. /// /// Some opcodes can only encode specific registers. -/// For example, many Thumb instructions only accept registers from `r0` to `r7` (the so-called *low* registers). -/// Other opcodes only encode a single register (which is then inferred from the opcode in question). +/// And yet other opcodes only encode a single register (which is then inferred from the opcode in question). +/// +/// # Low registers +/// +/// The registers whose identifiers can fit into `3` bits (i.e. registers from `r0` to `r7`, inclusive) are called *low* registers. +/// +/// Some instructions (primarily on Thumb) can only encode low registers. +/// In the case of Thumb, a few instructions can be used to move values to and from low registers. +/// +/// # High registers +/// +/// In contrast to low registers, registers that can only be addressed using `4` bíts are called *high registers*. +/// +/// Some instructions are pedantic about combining both low and high registers. #[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)] #[repr(u8)] pub enum Register { @@ -51,6 +66,20 @@ pub enum Register { } impl Register { + /// Converts the provided byte into a register identifier. + /// If the byte's value is not a valid identifier, [`None`] is returned. + /// + /// This conversion is valid for all `4`-bit values. + #[inline] + #[must_use] + pub const fn from_u8(value: u8) -> Option<Self> { + if value <= 0b1111 { + Some(unsafe { transmute::<u8, Self>(value) }) + } else { + None + } + } + /// Checks if the register is a low register. /// /// That is, it is any of `r0`, `r1`, `r2`, `r3`, `r4`, `r5`, `r6`, or `r7` -- or any alias herof. @@ -166,7 +195,7 @@ impl FromStr for Register { | "r15" => Ok(Pc), - _ => Err(Error::UnknownRegister) + _ => Err(Error::UnknownRegister(s.to_owned())) } } } |