93 lines
2.8 KiB
Rust
93 lines
2.8 KiB
Rust
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//! Contains tools (workarounds) to make implementing `const fn`s easier.
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/// Copies first `$len` bytes from `$slice` and returns them as an array.
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///
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/// Returns `None` if `$len > $slice.len()`. `$len` must be (obviously) statically known.
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/// Calling from non-const context doesn't affect performance.
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#[macro_export]
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macro_rules! copy_byte_array_from_slice {
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($slice:expr, $len:expr) => {
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if $len > $slice.len() {
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None
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} else {
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let mut array = [0u8; $len];
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// Note: produces same assemble as copy_from_slice
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let mut i = 0;
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while i < $len {
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array[i] = $slice[i];
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i += 1;
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}
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Some(array)
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}
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};
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}
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pub use copy_byte_array_from_slice;
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/// Concatenates two byte slices or byte arrays (or combination) to a single array.
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///
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/// # Panics
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///
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/// This macro panics if `$len` is not equal to the sum of `$a.len()` and `$b.len()`.
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#[macro_export]
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macro_rules! concat_bytes_to_arr {
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($a:expr, $b:expr, $len:expr) => {{
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// avoid repeated eval
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let a = $a;
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let b = $b;
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#[allow(unconditional_panic)]
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let _ = [(); 1][($len != a.len() + b.len()) as usize];
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let mut output = [0u8; $len];
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let mut i = 0;
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while i < a.len() {
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output[i] = $a[i];
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i += 1;
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}
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while i < a.len() + b.len() {
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output[i] = b[i - a.len()];
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i += 1;
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}
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output
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}};
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}
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pub use concat_bytes_to_arr;
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#[macro_export]
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/// Enables const fn in specified Rust version
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macro_rules! cond_const {
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($($(#[$attr:meta])* $vis:vis const(in $ver:ident $(= $human_ver:literal)?) fn $name:ident$(<$($gen:tt)*>)?($($args:tt)*) $(-> $ret:ty)? $body:block)+ ) => {
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$(
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#[cfg($ver)]
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$(#[$attr])*
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$(
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#[doc = "\nNote: the function is only `const` in Rust "]
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#[doc = $human_ver]
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#[doc = "."]
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)?
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$vis const fn $name$(<$($gen)*>)?($($args)*) $(-> $ret)? $body
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#[cfg(not($ver))]
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$(#[$attr])*
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$vis fn $name$(<$($gen)*>)?($($args)*) $(-> $ret)? $body
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)+
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};
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($($(#[$attr:meta])* $vis:vis const(in $ver:ident $(= $human_ver:literal)?) unsafe fn $name:ident$(<$($gen:tt)*>)?($($args:tt)*) $(-> $ret:ty)? $body:block)+ ) => {
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$(
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#[cfg($ver)]
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$(#[$attr])*
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$(
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#[doc = "\nNote: the function is only `const` in Rust "]
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#[doc = $human_ver]
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#[doc = " and newer."]
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)?
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$vis const unsafe fn $name$(<$($gen)*>)?($($args)*) $(-> $ret)? $body
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#[cfg(not($ver))]
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$(#[$attr])*
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$vis unsafe fn $name$(<$($gen)*>)?($($args)*) $(-> $ret)? $body
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)+
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};
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}
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pub use cond_const;
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