[PATCH v6 5/6] rust: str: add radix prefixed integer parsing functions

[Andreas Hindborg <a.hindborg@kernel.org>]

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 | 111 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index c102adac32757..192cd0ff5974f 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -945,3 +945,114 @@ 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::alloc::flags;
+    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', ..] => (16, &src[2..]),
+            [b'0', b'o' | b'O', ..] => (8, &src[2..]),
+            [b'0', b'b' | b'B', ..] => (2, &src[2..]),
+            [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 {
+        /// Parse a string according to the description in [`Self`].
+        fn from_str(src: &BStr) -> Result<Self> {
+            match src.iter().next() {
+                None => Err(EINVAL),
+                Some(sign @ b'-') | Some(sign @ b'+') => {
+                    let (radix, digits) = strip_radix(BStr::from_bytes(&src[1..]));
+                    let mut n_digits: KVec<u8> =
+                        KVec::with_capacity(digits.len() + 1, flags::GFP_KERNEL)?;
+                    n_digits.push(*sign, flags::GFP_KERNEL)?;
+                    n_digits.extend_from_slice(digits, flags::GFP_KERNEL)?;
+                    Self::from_str_radix(BStr::from_bytes(&n_digits), radix).map_err(|_| EINVAL)
+                }
+                Some(_) => {
+                    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