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tarcieritarcieri
committedJan 8, 2023
[WIP] cpubits: initial crate
As discussed in #824, adds a crate with the intent of it providing heuristics for selecting whether 32-bit or 64-bit backends have optimal codegen for a given target, with optional overrides. The intended use of this crate is in `build-dependencies`, where it can emit a `cfg` attribute (e.g. `--cfg cpubits="64"`) if one hasn't been explicitly specified already, and all gating on 32-bit vs 64-bit backends can simply use the `cfg` attribute.
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‎.github/workflows/cpubits.yml

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name: cpubits
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on:
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pull_request:
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paths:
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- "cpubits/**"
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- "Cargo.*"
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push:
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branches: master
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defaults:
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run:
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working-directory: cpubits
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env:
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CARGO_INCREMENTAL: 0
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RUSTFLAGS: "-Dwarnings"
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jobs:
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build:
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strategy:
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matrix:
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include:
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# 32-bit Linux/x86
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- target: i686-unknown-linux-gnu
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toolchain: 1.56.0 # MSRV
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deps: sudo apt update && sudo apt install gcc-multilib
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- target: i686-unknown-linux-gnu
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toolchain: stable
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deps: sudo apt update && sudo apt install gcc-multilib
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# 64-bit Linux/x86_64
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- target: x86_64-unknown-linux-gnu
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toolchain: 1.56.0 # MSRV
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- target: x86_64-unknown-linux-gnu
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toolchain: stable
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runs-on: ubuntu-latest
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steps:
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- uses: actions/checkout@v3
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- uses: RustCrypto/actions/cargo-cache@master
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- uses: dtolnay/rust-toolchain@master
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with:
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toolchain: ${{ matrix.toolchain }}
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targets: ${{ matrix.target }}
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- run: ${{ matrix.deps }}
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- run: cargo build --target ${{ matrix.target }}

‎Cargo.lock

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‎Cargo.toml

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"block-padding",
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"collectable",
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"cmov",
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"cpubits",
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"cpufeatures",
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"dbl",
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"fiat-constify",

‎cpubits/CHANGELOG.md

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# Changelog
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All notable changes to this project will be documented in this file.
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The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
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and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

‎cpubits/Cargo.toml

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[package]
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name = "cpubits"
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version = "0.0.0"
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description = "Configurable build-time selection of 32-bit or 64-bit backends"
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authors = ["RustCrypto Developers"]
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license = "MIT OR Apache-2.0"
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documentation = "https://docs.rs/cpubits"
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repository = "https://github.com/RustCrypto/utils/tree/master/cpubits"
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categories = []
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edition = "2018"
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readme = "README.md"

‎cpubits/LICENSE-APACHE

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Apache License
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‎cpubits/LICENSE-MIT

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Copyright (c) 2023 The RustCrypto Project Developers
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Permission is hereby granted, free of charge, to any
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person obtaining a copy of this software and associated
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documentation files (the "Software"), to deal in the
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Software without restriction, including without
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limitation the rights to use, copy, modify, merge,
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publish, distribute, sublicense, and/or sell copies of
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the Software, and to permit persons to whom the Software
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is furnished to do so, subject to the following
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conditions:
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The above copyright notice and this permission notice
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shall be included in all copies or substantial portions
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of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
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ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
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TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
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PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
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SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
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IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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DEALINGS IN THE SOFTWARE.

‎cpubits/README.md

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# [RustCrypto]: CPU bits selection
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[![crate][crate-image]][crate-link]
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[![Docs][docs-image]][docs-link]
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[![Build Status][build-image]][build-link]
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![Apache2/MIT licensed][license-image]
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![Rust Version][rustc-image]
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[![Project Chat][chat-image]][chat-link]
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Build-time selection for 32-bit vs 64-bit backends, with CPU-specific overrides
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for producing code with optimal performance.
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[Documentation][docs-link]
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## About
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Many algorithms support 32-bit and 64-bit backends, implemented using
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(often arrays of) `u32` or `u64`, in order to better support 32-bit or 64-bit
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targets.
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Selecting the optimal backend for a given target, however, is not quite as
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straightforward as introspecting `target_pointer_width` and choosing the
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backend that matches. Many 32-bit targets actually have better performance when
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using a backend based on `u64`, even if that isn't the CPU's native word size.
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Backend selection often has cross-cutting concerns across crates, which might
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need to agree on a common types for representing e.g. big integers as arrays
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of "limbs". This crate provides a single, common selection for the word size
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for a given target, with configurable overrides which also apply uniformly to
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all crates in a given project.
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## License
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Licensed under either of:
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* [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
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* [MIT license](http://opensource.org/licenses/MIT)
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at your option.
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### Contribution
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
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dual licensed as above, without any additional terms or conditions.
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[//]: # (badges)
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[crate-image]: https://img.shields.io/crates/v/cpubits.svg
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[crate-link]: https://crates.io/crates/cpubits
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[docs-image]: https://docs.rs/cpubits/badge.svg
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[docs-link]: https://docs.rs/cpubits/
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[build-image]: https://github.com/RustCrypto/utils/actions/workflows/cpubits.yml/badge.svg
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[build-link]: https://github.com/RustCrypto/utils/actions/workflows/cpubits.yml
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[license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
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[rustc-image]: https://img.shields.io/badge/rustc-1.56+-blue.svg
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[chat-image]: https://img.shields.io/badge/zulip-join_chat-blue.svg
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[chat-link]: https://rustcrypto.zulipchat.com/#narrow/stream/260052-utils
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[//]: # (general links)
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[RustCrypto]: https://github.com/rustcrypto

‎cpubits/src/lib.rs

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#![doc = include_str!("../README.md")]
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#![doc(
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html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",
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html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg"
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)]
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use std::fmt;
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/// Number of bits which should be treated as a CPU's "word size".
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#[derive(Clone, Copy, Debug, Eq, PartialEq)]
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#[repr(u8)]
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pub enum CpuBits {
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/// Use 32-bit backends for this target.
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B32 = 32,
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/// Use 64-bit backends for this target.
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B64 = 64,
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}
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impl CpuBits {
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/// Configure the build by emitting `rustcrypto_cpubits` cfg attributes.
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///
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/// This invokes [`Self::detect_with_cfg_overrides`] and emits the
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/// `rustcrypto_cpubits` cfg attributes, propagating the explicit selection
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/// if it's already been made.
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pub fn configure_build() {
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println!("{}", Self::detect_with_cfg_overrides());
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}
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/// Apply heuristics to autodetect an optimal number of bits for the
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/// current target.
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///
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/// Note that this may return values greater than a CPU's native word size
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/// in the event that codegen for a larger value is expected to provide
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/// better performance.
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///
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/// This function ignores `cfg(rustcrypto_cpubits)` overrides.
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pub fn detect() -> Self {
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// TODO(tarcieri): target-specific customizations for e.g. ARMV7, `wasm32`
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if cfg!(target_pointer_width = "64") {
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CpuBits::B64
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} else {
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CpuBits::B32
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}
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}
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/// Use `cfg(rustcrypto_cpubits)` overrides if configured, or otherwise
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/// fall back on [`CpuBits::detect`].
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///
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/// Ignores `cfg(rustcrypto_cpubits)` if it is set to a value other than
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/// "32" or "64". This is a limitation of `cfg` attributes.
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#[allow(dead_code)]
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pub fn detect_with_cfg_overrides() -> Self {
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#[cfg(rustcrypto_cpubits = "32")]
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return CpuBits::B32;
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#[cfg(rustcrypto_cpubits = "64")]
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return CpuBits::B64;
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CpuBits::detect()
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}
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}
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impl fmt::Display for CpuBits {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
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write!(f, "cargo:rustc-cfg=rustcrypto_cpubits=\"{}\"", *self as u8)
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}
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}

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