[PATCH v15 2/7] rust: str: add radix prefixed integer parsing functions

Andreas Hindborg
2025-07-07T13:32:13Z

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>
Suggested-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
rust/kernel/str.rs | 2 +
rust/kernel/str/parse_int.rs | 148 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 150 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index a927db8e079c3..2b6c8b4a0ae4b 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -8,6 +8,8 @@

use crate::prelude::*;

+pub mod parse_int;
+
/// Byte string without UTF-8 validity guarantee.
#[repr(transparent)]
pub struct BStr([u8]);
diff --git a/rust/kernel/str/parse_int.rs b/rust/kernel/str/parse_int.rs
new file mode 100644
index 0000000000000..48eb4c202984c
--- /dev/null
+++ b/rust/kernel/str/parse_int.rs
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Integer parsing functions.
+//!
+//! Integer parsing functions for parsing signed and unsigned integers
+//! potentially prefixed with `0x`, `0o`, or `0b`.
+
+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::prelude::*;
+ use crate::str::BStr;
+
+ /// Trait that allows parsing a [`&BStr`] to an integer with a radix.
+ pub trait FromStrRadix: Sized {
+ /// Parse `src` to [`Self`] using radix `radix`.
+ fn from_str_radix(src: &BStr, radix: u32) -> Result<Self>;
+
+ /// Tries to convert `value` into [`Self`] and negates the resulting value.
+ fn from_u64_negated(value: u64) -> Result<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)?;
+ Self::from_u64_negated(val)
+ }
+ _ => {
+ let (radix, digits) = strip_radix(src);
+ Self::from_str_radix(digits, radix).map_err(|_| EINVAL)
+ }
+ }
+ }
+}
+
+macro_rules! impl_parse_int {
+ ($($ty:ty),*) => {
+ $(
+ impl private::FromStrRadix for $ty {
+ fn from_str_radix(src: &BStr, radix: u32) -> Result<Self> {
+ <$ty>::from_str_radix(core::str::from_utf8(src).map_err(|_| EINVAL)?, radix)
+ .map_err(|_| EINVAL)
+ }
+
+ fn from_u64_negated(value: u64) -> Result<Self> {
+ const ABS_MIN: u64 = {
+ #[allow(unused_comparisons)]
+ if <$ty>::MIN < 0 {
+ 1u64 << (<$ty>::BITS - 1)
+ } else {
+ 0
+ }
+ };
+
+ if value > ABS_MIN {
+ return Err(EINVAL);
+ }
+
+ if value == ABS_MIN {
+ return Ok(<$ty>::MIN);
+ }
+
+ // SAFETY: The above checks guarantee that `value` fits into `Self`:
+ // - if `Self` is unsigned, then `ABS_MIN == 0` and thus we have returned above
+ // (either `EINVAL` or `MIN`).
+ // - if `Self` is signed, then we have that `0 <= value < ABS_MIN`. And since
+ // `ABS_MIN - 1` fits into `Self` by construction, `value` also does.
+ let value: Self = unsafe { value.try_into().unwrap_unchecked() };
+
+ Ok((!value).wrapping_add(1))
+ }
+ }
+
+ impl ParseInt for $ty {}
+ )*
+ };
+}
+
+impl_parse_int![i8, u8, i16, u16, i32, u32, i64, u64, isize, usize];

--
2.47.2