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Use boxed slices instead of vectors #181

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merged 2 commits into from Jun 9, 2020
Merged

Use boxed slices instead of vectors #181

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f76e59a
use boxed slices instead of vectors
newpavlov Jun 9, 2020
9d214df
describe why boxed slices are used
newpavlov Jun 9, 2020
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32 changes: 21 additions & 11 deletions digest/src/lib.rs
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Expand Up @@ -45,7 +45,7 @@ pub use dyn_digest::DynDigest;
use generic_array::{ArrayLength, GenericArray};

#[cfg(feature = "alloc")]
use alloc::vec::Vec;
use alloc::boxed::Box;

/// Trait for updating digest state with input data.
pub trait Update {
Expand Down Expand Up @@ -157,12 +157,16 @@ pub trait VariableOutput: core::marker::Sized {
/// will be equal to `output_size`.
fn finalize_variable<F: FnOnce(&[u8])>(self, f: F);

/// Retrieve result into vector and consume hasher.
/// Retrieve result into a boxed slice and consume hasher.
///
/// `Box<[u8]>` is used instead of `Vec<u8>` to save stack space, since
/// they have size of 2 and 3 words respectively.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
fn finalize_vec(self) -> Vec<u8> {
let mut buf = Vec::with_capacity(self.output_size());
self.finalize_variable(|res| buf.extend_from_slice(res));
fn finalize_box(self) -> Box<[u8]> {
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@tarcieri tarcieri Jun 9, 2020 •
edited

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Curious if finalize_boxed might make more sense here. I've seen both (e.g. box_clone seems common, but I've seen *_boxed as well)

let n = self.output_size();
let mut buf = vec![0u8; n].into_boxed_slice();
self.finalize_variable(|res| buf.copy_from_slice(res));
buf
}
}
Expand All @@ -173,13 +177,16 @@ pub trait XofReader {
/// Read output into the `buffer`. Can be called an unlimited number of times.
fn read(&mut self, buffer: &mut [u8]);

/// Read output into a vector of the specified size.
/// Read output into a boxed slice of the specified size.
///
/// Can be called an unlimited number of times in combination with `read`.
///
/// `Box<[u8]>` is used instead of `Vec<u8>` to save stack space, since
/// they have size of 2 and 3 words respectively.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
fn read_vec(&mut self, n: usize) -> Vec<u8> {
let mut buf = vec![0u8; n];
fn read_box(&mut self, n: usize) -> Box<[u8]> {
let mut buf = vec![0u8; n].into_boxed_slice();
self.read(&mut buf);
buf
}
Expand All @@ -193,11 +200,14 @@ pub trait ExtendableOutput: core::marker::Sized {
/// Retrieve XOF reader and consume hasher instance.
fn finalize_xof(self) -> Self::Reader;

/// Retrieve result into vector of specified length.
/// Retrieve result into a boxed slice of the specified size.
///
/// `Box<[u8]>` is used instead of `Vec<u8>` to save stack space, since
/// they have size of 2 and 3 words respectively.
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
fn finalize_vec(self, n: usize) -> Vec<u8> {
let mut buf = vec![0u8; n];
fn finalize_box(self, n: usize) -> Box<[u8]> {
let mut buf = vec![0u8; n].into_boxed_slice();
self.finalize_xof().read(&mut buf);
buf
}
Expand Down