13f2749021
# Objective The `generate_composite_uuid` utility function hidden in `bevy_reflect::__macro_exports` could be generally useful to users. For example, I previously relied on `Hash` to generate a `u64` to create a deterministic `HandleId`. In v0.12, `HandleId` has been replaced by `AssetId` which now requires a `Uuid`, which I could generate with this function. ## Solution Relocate `generate_composite_uuid` from `bevy_reflect::__macro_exports` to `bevy_utils::uuid`. It is still re-exported under `bevy_reflect::__macro_exports` so there should not be any breaking changes (although, users should generally not rely on pseudo-private/hidden modules like `__macro_exports`). I chose to keep it in `bevy_reflect::__macro_exports` so as to not clutter up our public API and to reduce the number of changes in this PR. We could have also marked the export as `#[doc(hidden)]`, but personally I like that we have a dedicated module for this (makes it clear what is public and what isn't when just looking at the macro code). --- ## Changelog - Moved `generate_composite_uuid` to `bevy_utils::uuid` and made it public - Note: it was technically already public, just hidden
36 lines
1.3 KiB
Rust
36 lines
1.3 KiB
Rust
//! UUID utilities.
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//!
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//! This module re-exports the [`Uuid`] type from the [`uuid`] crate,
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//! and provides additional utility functions.
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//!
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//! [`uuid`]: ::uuid
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pub use ::uuid::Uuid;
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/// Generates a new UUID from the given UUIDs `a` and `b`,
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/// where the bytes are generated by a bitwise `a ^ b.rotate_right(1)`.
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///
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/// The generated UUID will be a `UUIDv4`
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/// (meaning that the bytes should be random, not e.g. derived from the system time).
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#[allow(clippy::unusual_byte_groupings)] // unusual byte grouping is meant to signal the relevant bits
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pub const fn generate_composite_uuid(a: Uuid, b: Uuid) -> Uuid {
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let mut new = [0; 16];
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let mut i = 0;
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while i < new.len() {
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// rotating ensures different uuids for A<B<C>> and B<A<C>> because: A ^ (B ^ C) = B ^ (A ^ C)
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// notice that you have to rotate the second parameter: A.rr ^ (B.rr ^ C) = B.rr ^ (A.rr ^ C)
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// Solution: A ^ (B ^ C.rr).rr != B ^ (A ^ C.rr).rr
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new[i] = a.as_bytes()[i] ^ b.as_bytes()[i].rotate_right(1);
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i += 1;
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}
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// Version: the most significant 4 bits in the 6th byte: 11110000
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new[6] = new[6] & 0b0000_1111 | 0b0100_0000; // set version to v4
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// Variant: the most significant 3 bits in the 8th byte: 11100000
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new[8] = new[8] & 0b000_11111 | 0b100_00000; // set variant to rfc4122
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Uuid::from_bytes(new)
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}
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