[PATCH v7 5/6] rust: str: add radix prefixed integer parsing functions

Andreas Hindborg
2025-02-18T13:01:53Z

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.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
rust/kernel/str.rs | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 118 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index db272d2198fcc..8b0d814b47f52 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -945,3 +945,121 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
macro_rules! fmt {
($($f:tt)*) => ( core::format_args!($($f)*) )
}
+
+pub mod parse_int {
+ //! 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;
+
+ /// Trait that allows parsing a [`&BStr`] to an integer with a radix.
+ ///
+ /// [`&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 trait FromStrRadix: Sized {
+ /// Parse `src` to `Self` using radix `radix`.
+ fn from_str_radix(src: &BStr, radix: u32) -> Result<Self, crate::error::Error>;
+ }
+
+ /// 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://www.kernel.org/doc/html/latest/core-api/kernel-api.html#c.kstrtol
+ /// [`kstrtoul()`]: https://www.kernel.org/doc/html/latest/core-api/kernel-api.html#c.kstrtoul
+ ///
+ /// # Example
+ /// ```
+ /// use kernel::str::parse_int::ParseInt;
+ /// use kernel::b_str;
+ ///
+ /// assert_eq!(Ok(0), 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(127), i8::from_str(b_str!("127")));
+ /// assert!(i8::from_str(b_str!("128")).is_err());
+ /// assert_eq!(Ok(-128), i8::from_str(b_str!("-128")));
+ /// assert!(i8::from_str(b_str!("-129")).is_err());
+ /// assert_eq!(Ok(255), u8::from_str(b_str!("255")));
+ /// assert!(u8::from_str(b_str!("256")).is_err());
+ /// ```
+ pub trait ParseInt: FromStrRadix + TryFrom<i128> {
+ /// 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 i128 as sufficiently large.
+ let val = i128::from_str_radix(
+ core::str::from_utf8(digits).map_err(|_| EINVAL)?,
+ radix,
+ )
+ .map_err(|_| EINVAL)?;
+ let val = -val;
+ val.try_into().map_err(|_| EINVAL)
+ }
+ _ => {
+ let (radix, digits) = strip_radix(src);
+ Self::from_str_radix(digits, radix).map_err(|_| EINVAL)
+ }
+ }
+ }
+ }
+
+ macro_rules! impl_parse_int {
+ ($ty:ty) => {
+ impl FromStrRadix for $ty {
+ fn from_str_radix(src: &BStr, radix: u32) -> Result<Self, crate::error::Error> {
+ <$ty>::from_str_radix(core::str::from_utf8(src).map_err(|_| EINVAL)?, radix)
+ .map_err(|_| EINVAL)
+ }
+ }
+
+ 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);
+}

--
2.47.0