[PATCH v12 1/3] rust: str: add radix prefixed integer parsing functions

Andreas Hindborg
2025-05-06T13:02:48Z

Add the trait `ParseInt` for parsing string representations of integers
where the string representations are optionally prefixed by a radix
specifier. Implement the trait for the primitive integer types.

Tested-by: Daniel Gomez <da.gomez@samsung.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
rust/kernel/str.rs | 172 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 171 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 878111cb77bc..174e70397305 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -573,7 +573,6 @@ macro_rules! c_str {
}

#[cfg(test)]
-#[expect(clippy::items_after_test_module)]
mod tests {
use super::*;

@@ -946,3 +945,174 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
macro_rules! fmt {
($($f:tt)*) => ( core::format_args!($($f)*) )
}
+
+/// Integer parsing functions for parsing signed and unsigned integers
+/// potentially prefixed with `0x`, `0o`, or `0b`.
+pub mod parse_int {
+ use crate::prelude::*;
+ use crate::str::BStr;
+ use core::ops::Deref;
+
+ // Make `FromStrRadix` a public type with a private name. This seals
+ // `ParseInt`, that is, prevents downstream users from implementing the
+ // trait.
+ mod private {
+ use crate::str::BStr;
+
+ /// Trait that allows parsing a [`&BStr`] to an integer with a radix.
+ ///
+ /// # Safety
+ ///
+ /// The member functions of this trait must be implemented according to
+ /// their documentation.
+ ///
+ /// [`&BStr`]: kernel::str::BStr
+ // This is required because the `from_str_radix` function on the primitive
+ // integer types is not part of any trait.
+ pub unsafe trait FromStrRadix: Sized {
+ /// The minimum value this integer type can assume.
+ const MIN: Self;
+
+ /// Parse `src` to [`Self`] using radix `radix`.
+ fn from_str_radix(src: &BStr, radix: u32) -> Result<Self, crate::error::Error>;
+
+ /// Return the absolute value of [`Self::MIN`].
+ fn abs_min() -> u64;
+
+ /// Perform bitwise 2's complement on `self`.
+ ///
+ /// Note: This function does not make sense for unsigned integers.
+ fn complement(self) -> Self;
+ }
+ }
+
+ /// Extract the radix from an integer literal optionally prefixed with
+ /// one of `0x`, `0X`, `0o`, `0O`, `0b`, `0B`, `0`.
+ fn strip_radix(src: &BStr) -> (u32, &BStr) {
+ match src.deref() {
+ [b'0', b'x' | b'X', rest @ ..] => (16, rest.as_ref()),
+ [b'0', b'o' | b'O', rest @ ..] => (8, rest.as_ref()),
+ [b'0', b'b' | b'B', rest @ ..] => (2, rest.as_ref()),
+ // NOTE: We are including the leading zero to be able to parse
+ // literal `0` here. If we removed it as a radix prefix, we would
+ // not be able to parse `0`.
+ [b'0', ..] => (8, src),
+ _ => (10, src),
+ }
+ }
+
+ /// Trait for parsing string representations of integers.
+ ///
+ /// Strings beginning with `0x`, `0o`, or `0b` are parsed as hex, octal, or
+ /// binary respectively. Strings beginning with `0` otherwise are parsed as
+ /// octal. Anything else is parsed as decimal. A leading `+` or `-` is also
+ /// permitted. Any string parsed by [`kstrtol()`] or [`kstrtoul()`] will be
+ /// successfully parsed.
+ ///
+ /// [`kstrtol()`]: https://docs.kernel.org/core-api/kernel-api.html#c.kstrtol
+ /// [`kstrtoul()`]: https://docs.kernel.org/core-api/kernel-api.html#c.kstrtoul
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// # use kernel::str::parse_int::ParseInt;
+ /// # use kernel::b_str;
+ ///
+ /// assert_eq!(Ok(0u8), u8::from_str(b_str!("0")));
+ ///
+ /// assert_eq!(Ok(0xa2u8), u8::from_str(b_str!("0xa2")));
+ /// assert_eq!(Ok(-0xa2i32), i32::from_str(b_str!("-0xa2")));
+ ///
+ /// assert_eq!(Ok(-0o57i8), i8::from_str(b_str!("-0o57")));
+ /// assert_eq!(Ok(0o57i8), i8::from_str(b_str!("057")));
+ ///
+ /// assert_eq!(Ok(0b1001i16), i16::from_str(b_str!("0b1001")));
+ /// assert_eq!(Ok(-0b1001i16), i16::from_str(b_str!("-0b1001")));
+ ///
+ /// assert_eq!(Ok(127i8), i8::from_str(b_str!("127")));
+ /// assert!(i8::from_str(b_str!("128")).is_err());
+ /// assert_eq!(Ok(-128i8), i8::from_str(b_str!("-128")));
+ /// assert!(i8::from_str(b_str!("-129")).is_err());
+ /// assert_eq!(Ok(255u8), u8::from_str(b_str!("255")));
+ /// assert!(u8::from_str(b_str!("256")).is_err());
+ /// ```
+ pub trait ParseInt: private::FromStrRadix + TryFrom<u64> {
+ /// Parse a string according to the description in [`Self`].
+ fn from_str(src: &BStr) -> Result<Self> {
+ match src.deref() {
+ [b'-', rest @ ..] => {
+ let (radix, digits) = strip_radix(rest.as_ref());
+ // 2's complement values range from -2^(b-1) to 2^(b-1)-1.
+ // So if we want to parse negative numbers as positive and
+ // later multiply by -1, we have to parse into a larger
+ // integer. We choose `u64` as sufficiently large.
+ //
+ // NOTE: 128 bit integers are not available on all
+ // platforms, hence the choice of 64 bits.
+ let val = u64::from_str_radix(
+ core::str::from_utf8(digits).map_err(|_| EINVAL)?,
+ radix,
+ )
+ .map_err(|_| EINVAL)?;
+
+ if val > Self::abs_min() {
+ return Err(EINVAL);
+ }
+
+ if val == Self::abs_min() {
+ return Ok(Self::MIN);
+ }
+
+ // SAFETY: We checked that `val` will fit in `Self` above.
+ let val: Self = unsafe { val.try_into().unwrap_unchecked() };
+
+ Ok(val.complement())
+ }
+ _ => {
+ let (radix, digits) = strip_radix(src);
+ Self::from_str_radix(digits, radix).map_err(|_| EINVAL)
+ }
+ }
+ }
+ }
+
+ macro_rules! impl_parse_int {
+ ($ty:ty) => {
+ // SAFETY: We implement the trait according to the documentation.
+ unsafe impl private::FromStrRadix for $ty {
+ const MIN: Self = <$ty>::MIN;
+
+ fn from_str_radix(src: &BStr, radix: u32) -> Result<Self, crate::error::Error> {
+ <$ty>::from_str_radix(core::str::from_utf8(src).map_err(|_| EINVAL)?, radix)
+ .map_err(|_| EINVAL)
+ }
+
+ fn abs_min() -> u64 {
+ #[allow(unused_comparisons)]
+ if Self::MIN < 0 {
+ 1u64 << (Self::BITS - 1)
+ } else {
+ 0
+ }
+ }
+
+ fn complement(self) -> Self {
+ (!self).wrapping_add((1 as $ty))
+ }
+ }
+
+ impl ParseInt for $ty {}
+ };
+ }
+
+ impl_parse_int!(i8);
+ impl_parse_int!(u8);
+ impl_parse_int!(i16);
+ impl_parse_int!(u16);
+ impl_parse_int!(i32);
+ impl_parse_int!(u32);
+ impl_parse_int!(i64);
+ impl_parse_int!(u64);
+ impl_parse_int!(isize);
+ impl_parse_int!(usize);
+}

--
2.47.2