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//! Miscelaneous functions. //! //! # Features //! //! This module is only exported with the "fmt" feature. use core::ops::Range; /// Newtype wrapper to get around limitations in `const fn`s pub(crate) struct Constructor<T>(fn() -> T); /// A const equivalent of `&str` equality comparison. /// /// # Example /// /// ```rust /// use const_format::utils::str_eq; /// /// const STRS: &[&str] = &[ /// "foo", /// "fooooo", /// "bar", /// "baz", /// ]; /// /// const ARE_0_0_EQ: bool = str_eq(STRS[0], STRS[0]); /// const ARE_0_1_EQ: bool = str_eq(STRS[0], STRS[1]); /// /// const ARE_1_1_EQ: bool = str_eq(STRS[1], STRS[1]); /// const ARE_1_2_EQ: bool = str_eq(STRS[1], STRS[2]); /// /// const ARE_2_2_EQ: bool = str_eq(STRS[2], STRS[2]); /// const ARE_2_3_EQ: bool = str_eq(STRS[2], STRS[3]); /// /// assert!( ARE_0_0_EQ ); /// assert!( !ARE_0_1_EQ ); /// /// assert!( ARE_1_1_EQ ); /// assert!( !ARE_1_2_EQ ); /// /// assert!( ARE_2_2_EQ ); /// assert!( !ARE_2_3_EQ ); /// /// ``` /// pub const fn str_eq(left: &str, right: &str) -> bool { u8_slice_eq(left.as_bytes(), right.as_bytes()) } /// A const equivalent of `&[u8]` equality comparison. /// /// # Example /// /// ```rust /// use const_format::utils::u8_slice_eq; /// /// const SLICES: &[&[u8]] = &[ /// &[10, 20], /// &[10, 20, 30, 40], /// &[3, 5, 8, 13], /// &[4, 9, 16, 25], /// ]; /// /// const ARE_0_0_EQ: bool = u8_slice_eq(SLICES[0], SLICES[0]); /// const ARE_0_1_EQ: bool = u8_slice_eq(SLICES[0], SLICES[1]); /// /// const ARE_1_1_EQ: bool = u8_slice_eq(SLICES[1], SLICES[1]); /// const ARE_1_2_EQ: bool = u8_slice_eq(SLICES[1], SLICES[2]); /// /// const ARE_2_2_EQ: bool = u8_slice_eq(SLICES[2], SLICES[2]); /// const ARE_2_3_EQ: bool = u8_slice_eq(SLICES[2], SLICES[3]); /// /// assert!( ARE_0_0_EQ ); /// assert!( !ARE_0_1_EQ ); /// /// assert!( ARE_1_1_EQ ); /// assert!( !ARE_1_2_EQ ); /// /// assert!( ARE_2_2_EQ ); /// assert!( !ARE_2_3_EQ ); /// /// ``` /// pub const fn u8_slice_eq(left: &[u8], right: &[u8]) -> bool { if left.len() != right.len() { return false; } let mut i = 0; while i != left.len() { if left[i] != right[i] { return false; } i += 1; } true } #[doc(hidden)] #[inline] pub const fn saturate_range(s: &[u8], range: &Range<usize>) -> Range<usize> { let len = s.len(); let end = min_usize(range.end, len); min_usize(range.start, end)..end } #[doc(hidden)] #[cfg(feature = "constant_time_as_str")] pub union Dereference<'a, T: ?Sized> { pub ptr: *const T, pub reff: &'a T, } //////////////////////////////////////////////////////////////////////////////// macro_rules! slice_up_to_len_alt_docs { ($item:item) => { /// A const equivalent of `&slice[..len]`. /// /// If `slice.len() < len`, this simply returns `slice` back. /// /// # Runtime /// /// If the "constant_time_as_str" feature is disabled, /// thich takes linear time to remove the trailing elements, /// proportional to `slice.len() - len`. /// /// If the "constant_time_as_str" feature is enabled, it takes constant time to run, /// but uses a few additional nightly features. /// /// # Example /// /// ```rust /// use const_format::utils::slice_up_to_len_alt; /// /// const FIBB: &[u16] = &[3, 5, 8, 13, 21, 34, 55, 89]; /// /// const TWO: &[u16] = slice_up_to_len_alt(FIBB, 2); /// const FOUR: &[u16] = slice_up_to_len_alt(FIBB, 4); /// const ALL: &[u16] = slice_up_to_len_alt(FIBB, usize::MAX); /// /// assert_eq!(TWO, &[3, 5]); /// assert_eq!(FOUR, &[3, 5, 8, 13]); /// assert_eq!(FIBB, ALL); /// /// ``` $item }; } slice_up_to_len_alt_docs! { #[cfg(feature = "constant_time_as_str")] #[inline(always)] pub const fn slice_up_to_len_alt<T>(slice: &[T], len: usize) -> &[T] { slice_up_to_len(slice, len) } } slice_up_to_len_alt_docs! { #[cfg(not(feature = "constant_time_as_str"))] pub const fn slice_up_to_len_alt<T>(slice: &[T], len: usize) -> &[T] { let mut rem = slice.len().saturating_add(1).saturating_sub(len); let mut ret = slice; if rem == 0 { return slice; } macro_rules! slice_up_to_len_alt_impl{ ( $( ($len:expr, [$($ignored:tt)*]) )* )=>{ $( while rem > $len { if let [next @ .., $($ignored)* ] = ret { ret = next; rem -= $len; } } )* } } slice_up_to_len_alt_impl!{ (36, [_, _, _, _, _, _,_, _, _, _, _, _,_, _, _, _, _, _,_, _, _, _, _, _,_, _, _, _, _, _,_, _, _, _, _, _,]) (6, [_, _, _, _, _, _]) (1, [_]) } ret } } //////////////////////////////////////////////////////////////////////////////// macro_rules! slice_up_to_len_docs { ($item:item) => { /// A conditionally-const equivalent of `&slice[..len]`. /// /// If `slice.len() < len`, this simply returns `slice` back. /// /// # Constness /// /// This function takes constant time, /// and in order to be `const fn` it requires the "constant_time_as_str" /// feature to be enabled, /// because this function uses some additional nightly Rust features. /// /// # Example /// /// ```rust /// use const_format::utils::slice_up_to_len_alt; /// /// const FIBB: &[u16] = &[3, 5, 8, 13, 21, 34, 55, 89]; /// /// const TWO: &[u16] = slice_up_to_len_alt(FIBB, 2); /// const FOUR: &[u16] = slice_up_to_len_alt(FIBB, 4); /// const ALL: &[u16] = slice_up_to_len_alt(FIBB, usize::MAX); /// /// assert_eq!(TWO, &[3, 5]); /// assert_eq!(FOUR, &[3, 5, 8, 13]); /// assert_eq!(FIBB, ALL); /// /// ``` $item }; } slice_up_to_len_docs! { #[cfg(feature = "constant_time_as_str")] #[inline] pub const fn slice_up_to_len<T>(slice: &[T], len: usize) -> &[T] { if len > slice.len() { return slice; } // Doing this to get a slice up to length at compile-time unsafe { let raw_slice = core::ptr::slice_from_raw_parts(slice.as_ptr(), len); Dereference { ptr: raw_slice }.reff } } } slice_up_to_len_docs! { #[cfg(not(feature = "constant_time_as_str"))] #[inline] pub fn slice_up_to_len<T>(slice: &[T], len: usize) -> &[T] { if len > slice.len() { return slice; } &slice[..len] } } //////////////////////////////////////////////////////////////////////////////// pub(crate) const fn min_usize(l: usize, r: usize) -> usize { if l < r { l } else { r } } #[cfg(test)] mod tests { use super::*; #[test] fn slice_eq_test() { assert!(u8_slice_eq(&[], &[])); assert!(!u8_slice_eq(&[], &[0])); assert!(!u8_slice_eq(&[0], &[])); assert!(u8_slice_eq(&[0], &[0])); assert!(!u8_slice_eq(&[0], &[1])); assert!(!u8_slice_eq(&[1], &[0])); assert!(!u8_slice_eq(&[0], &[0, 1])); assert!(!u8_slice_eq(&[0, 1], &[0])); assert!(u8_slice_eq(&[0, 1], &[0, 1])); assert!(!u8_slice_eq(&[0, 1], &[0, 2])); } #[test] fn str_eq_test() { assert!(str_eq("", "")); assert!(!str_eq("", "0")); assert!(!str_eq("0", "")); assert!(str_eq("0", "0")); assert!(!str_eq("0", "1")); assert!(!str_eq("1", "0")); assert!(!str_eq("0", "0, 1")); assert!(!str_eq("0, 1", "0")); assert!(!str_eq("0, 1", "1")); assert!(str_eq("0, 1", "0, 1")); assert!(!str_eq("0, 1", "0, 2")); } #[test] fn test_slice_up_to_len_alt() { let mut list = [0u16; 256]; (100..).zip(list.iter_mut()).for_each(|(i, m)| *m = i); for i in 0..list.len() { assert_eq!(slice_up_to_len_alt(&list, i), &list[..i]); } } #[test] fn slice_in_bounds() { assert_eq!(slice_up_to_len(&[3, 5], 0), []); assert_eq!(slice_up_to_len(&[3, 5], 1), [3]); assert_eq!(slice_up_to_len(&[3, 5], 2), [3, 5]); assert_eq!(slice_up_to_len(&[3, 5], 3), [3, 5]); assert_eq!(slice_up_to_len(&[3, 5], 4), [3, 5]); } }