/rust/registry/src/index.crates.io-1949cf8c6b5b557f/fastrand-2.3.0/src/global_rng.rs

Source
//! A global, thread-local random number generator.

use crate::Rng;

use std::cell::Cell;
use std::ops::RangeBounds;
use std::vec::Vec;

// Chosen by fair roll of the dice.
const DEFAULT_RNG_SEED: u64 = 0xef6f79ed30ba75a;

impl Default for Rng {
    /// Initialize the `Rng` from the system's random number generator.
    ///
    /// This is equivalent to [`Rng::new()`].
    #[inline]
    fn default() -> Rng {
        Rng::new()
    }
}

impl Rng {
    /// Creates a new random number generator.
    #[inline]
    pub fn new() -> Rng {
        try_with_rng(Rng::fork).unwrap_or_else(|_| Rng::with_seed(0x4d595df4d0f33173))
    }
}

std::thread_local! {
    static RNG: Cell<Rng> = Cell::new(Rng(random_seed().unwrap_or(DEFAULT_RNG_SEED)));
}

/// Run an operation with the current thread-local generator.
#[inline]
fn with_rng<R>(f: impl FnOnce(&mut Rng) -> R) -> R {
    RNG.with(|rng| {
        let current = rng.replace(Rng(0));

        let mut restore = RestoreOnDrop { rng, current };

        f(&mut restore.current)
    })
}

/// Try to run an operation with the current thread-local generator.
#[inline]
fn try_with_rng<R>(f: impl FnOnce(&mut Rng) -> R) -> Result<R, std::thread::AccessError> {
    RNG.try_with(|rng| {
        let current = rng.replace(Rng(0));

        let mut restore = RestoreOnDrop { rng, current };

        f(&mut restore.current)
    })
}

/// Make sure the original RNG is restored even on panic.
struct RestoreOnDrop<'a> {
    rng: &'a Cell<Rng>,
    current: Rng,
}

impl Drop for RestoreOnDrop<'_> {
    fn drop(&mut self) {
        self.rng.set(Rng(self.current.0));
    }
}

/// Initializes the thread-local generator with the given seed.
#[inline]
pub fn seed(seed: u64) {
    with_rng(|r| r.seed(seed));
}

/// Gives back **current** seed that is being held by the thread-local generator.
#[inline]
pub fn get_seed() -> u64 {
    with_rng(|r| r.get_seed())
}

/// Generates a random `bool`.
#[inline]
pub fn bool() -> bool {
    with_rng(|r| r.bool())
}

/// Generates a random `char` in ranges a-z and A-Z.
#[inline]
pub fn alphabetic() -> char {
    with_rng(|r| r.alphabetic())
}

/// Generates a random `char` in ranges a-z, A-Z and 0-9.
#[inline]
pub fn alphanumeric() -> char {
    with_rng(|r| r.alphanumeric())
}

/// Generates a random `char` in range a-z.
#[inline]
pub fn lowercase() -> char {
    with_rng(|r| r.lowercase())
}

/// Generates a random `char` in range A-Z.
#[inline]
pub fn uppercase() -> char {
    with_rng(|r| r.uppercase())
}

/// Choose an item from an iterator at random.
///
/// This function may have an unexpected result if the `len()` property of the
/// iterator does not match the actual number of items in the iterator. If
/// the iterator is empty, this returns `None`.
#[inline]
pub fn choice<I>(iter: I) -> Option<I::Item>
where
    I: IntoIterator,
    I::IntoIter: ExactSizeIterator,
{
    with_rng(|r| r.choice(iter))
}

/// Generates a random digit in the given `base`.
///
/// Digits are represented by `char`s in ranges 0-9 and a-z.
///
/// Panics if the base is zero or greater than 36.
#[inline]
pub fn digit(base: u32) -> char {
    with_rng(|r| r.digit(base))
}

/// Shuffles a slice randomly.
#[inline]
pub fn shuffle<T>(slice: &mut [T]) {
    with_rng(|r| r.shuffle(slice))
}

/// Fill a byte slice with random data.
#[inline]
pub fn fill(slice: &mut [u8]) {
    with_rng(|r| r.fill(slice))
}

macro_rules! integer {
    ($t:tt, $doc:tt) => {
        #[doc = $doc]
        ///
        /// Panics if the range is empty.
        #[inline]
        pub fn $t(range: impl RangeBounds<$t>) -> $t {
            with_rng(|r| r.$t(range))
        }
    };
}

integer!(u8, "Generates a random `u8` in the given range.");
integer!(i8, "Generates a random `i8` in the given range.");
integer!(u16, "Generates a random `u16` in the given range.");
integer!(i16, "Generates a random `i16` in the given range.");
integer!(u32, "Generates a random `u32` in the given range.");
integer!(i32, "Generates a random `i32` in the given range.");
integer!(u64, "Generates a random `u64` in the given range.");
integer!(i64, "Generates a random `i64` in the given range.");
integer!(u128, "Generates a random `u128` in the given range.");
integer!(i128, "Generates a random `i128` in the given range.");
integer!(usize, "Generates a random `usize` in the given range.");
integer!(isize, "Generates a random `isize` in the given range.");
integer!(char, "Generates a random `char` in the given range.");

/// Generates a random `f32` in range `0..1`.
pub fn f32() -> f32 {
    with_rng(|r| r.f32())
}

/// Generates a random `f64` in range `0..1`.
pub fn f64() -> f64 {
    with_rng(|r| r.f64())
}

/// Collects `amount` values at random from the iterable into a vector.
pub fn choose_multiple<I: IntoIterator>(source: I, amount: usize) -> Vec<I::Item> {
    with_rng(|rng| rng.choose_multiple(source, amount))
}

#[cfg(not(all(
    any(target_arch = "wasm32", target_arch = "wasm64"),
    target_os = "unknown"
)))]
fn random_seed() -> Option<u64> {
    use std::collections::hash_map::DefaultHasher;
    use std::hash::{Hash, Hasher};
    use std::thread;
    use std::time::Instant;

    let mut hasher = DefaultHasher::new();
    Instant::now().hash(&mut hasher);
    thread::current().id().hash(&mut hasher);
    Some(hasher.finish())
}

#[cfg(all(
    any(target_arch = "wasm32", target_arch = "wasm64"),
    target_os = "unknown",
    feature = "js"
))]
fn random_seed() -> Option<u64> {
    // TODO(notgull): Failures should be logged somewhere.
    let mut seed = [0u8; 8];
    getrandom::getrandom(&mut seed).ok()?;
    Some(u64::from_ne_bytes(seed))
}

#[cfg(all(
    any(target_arch = "wasm32", target_arch = "wasm64"),
    target_os = "unknown",
    not(feature = "js")
))]
fn random_seed() -> Option<u64> {
    None
}

Coverage Report

Created: 2025-11-16 06:37

Line	Count	Source
1		//! A global, thread-local random number generator.
2
3		use crate::Rng;
4
5		use std::cell::Cell;
6		use std::ops::RangeBounds;
7		use std::vec::Vec;
8
9		// Chosen by fair roll of the dice.
10		const DEFAULT_RNG_SEED: u64 = 0xef6f79ed30ba75a;
11
12		impl Default for Rng {
13		/// Initialize the `Rng` from the system's random number generator.
14		///
15		/// This is equivalent to [`Rng::new()`].
16		#[inline]
17	0	fn default() -> Rng {
18	0	Rng::new()
19	0	}
20		}
21
22		impl Rng {
23		/// Creates a new random number generator.
24		#[inline]
25	0	pub fn new() -> Rng {
26	0	try_with_rng(Rng::fork).unwrap_or_else(\|_\| Rng::with_seed(0x4d595df4d0f33173)) Unexecuted instantiation: <fastrand::Rng>::new::{closure#0} Unexecuted instantiation: <fastrand::Rng>::new::{closure#0}
27	0	} Unexecuted instantiation: <fastrand::Rng>::new Unexecuted instantiation: <fastrand::Rng>::new
28		}
29
30		std::thread_local! {
31		static RNG: Cell<Rng> = Cell::new(Rng(random_seed().unwrap_or(DEFAULT_RNG_SEED)));
32		}
33
34		/// Run an operation with the current thread-local generator.
35		#[inline]
36	0	fn with_rng<R>(f: impl FnOnce(&mut Rng) -> R) -> R {
37	0	RNG.with(\|rng\| {
38	0	let current = rng.replace(Rng(0));
39
40	0	let mut restore = RestoreOnDrop { rng, current };
41
42	0	f(&mut restore.current)
43	0	}) Unexecuted instantiation: fastrand::global_rng::with_rng::<f64, fastrand::global_rng::f64::{closure#0}>::{closure#0} Unexecuted instantiation: fastrand::global_rng::with_rng::<f32, fastrand::global_rng::f32::{closure#0}>::{closure#0}
44	0	} Unexecuted instantiation: fastrand::global_rng::with_rng::<f64, fastrand::global_rng::f64::{closure#0}> Unexecuted instantiation: fastrand::global_rng::with_rng::<f32, fastrand::global_rng::f32::{closure#0}>
45
46		/// Try to run an operation with the current thread-local generator.
47		#[inline]
48	0	fn try_with_rng<R>(f: impl FnOnce(&mut Rng) -> R) -> Result<R, std::thread::AccessError> {
49	0	RNG.try_with(\|rng\| {
50	0	let current = rng.replace(Rng(0));
51
52	0	let mut restore = RestoreOnDrop { rng, current };
53
54	0	f(&mut restore.current)
55	0	}) Unexecuted instantiation: fastrand::global_rng::try_with_rng::<fastrand::Rng, <fastrand::Rng>::fork>::{closure#0} Unexecuted instantiation: fastrand::global_rng::try_with_rng::<_, _>::{closure#0}
56	0	} Unexecuted instantiation: fastrand::global_rng::try_with_rng::<fastrand::Rng, <fastrand::Rng>::fork> Unexecuted instantiation: fastrand::global_rng::try_with_rng::<_, _>
57
58		/// Make sure the original RNG is restored even on panic.
59		struct RestoreOnDrop<'a> {
60		rng: &'a Cell<Rng>,
61		current: Rng,
62		}
63
64		impl Drop for RestoreOnDrop<'_> {
65	0	fn drop(&mut self) {
66	0	self.rng.set(Rng(self.current.0));
67	0	}
68		}
69
70		/// Initializes the thread-local generator with the given seed.
71		#[inline]
72	0	pub fn seed(seed: u64) {
73	0	with_rng(\|r\| r.seed(seed));
74	0	}
75
76		/// Gives back current seed that is being held by the thread-local generator.
77		#[inline]
78	0	pub fn get_seed() -> u64 {
79	0	with_rng(\|r\| r.get_seed())
80	0	}
81
82		/// Generates a random `bool`.
83		#[inline]
84	0	pub fn bool() -> bool {
85	0	with_rng(\|r\| r.bool())
86	0	}
87
88		/// Generates a random `char` in ranges a-z and A-Z.
89		#[inline]
90	0	pub fn alphabetic() -> char {
91	0	with_rng(\|r\| r.alphabetic())
92	0	}
93
94		/// Generates a random `char` in ranges a-z, A-Z and 0-9.
95		#[inline]
96	0	pub fn alphanumeric() -> char {
97	0	with_rng(\|r\| r.alphanumeric())
98	0	}
99
100		/// Generates a random `char` in range a-z.
101		#[inline]
102	0	pub fn lowercase() -> char {
103	0	with_rng(\|r\| r.lowercase())
104	0	}
105
106		/// Generates a random `char` in range A-Z.
107		#[inline]
108	0	pub fn uppercase() -> char {
109	0	with_rng(\|r\| r.uppercase())
110	0	}
111
112		/// Choose an item from an iterator at random.
113		///
114		/// This function may have an unexpected result if the `len()` property of the
115		/// iterator does not match the actual number of items in the iterator. If
116		/// the iterator is empty, this returns `None`.
117		#[inline]
118	0	pub fn choice<I>(iter: I) -> Option<I::Item>
119	0	where
120	0	I: IntoIterator,
121	0	I::IntoIter: ExactSizeIterator,
122		{
123	0	with_rng(\|r\| r.choice(iter))
124	0	}
125
126		/// Generates a random digit in the given `base`.
127		///
128		/// Digits are represented by `char`s in ranges 0-9 and a-z.
129		///
130		/// Panics if the base is zero or greater than 36.
131		#[inline]
132	0	pub fn digit(base: u32) -> char {
133	0	with_rng(\|r\| r.digit(base))
134	0	}
135
136		/// Shuffles a slice randomly.
137		#[inline]
138	0	pub fn shuffle<T>(slice: &mut [T]) {
139	0	with_rng(\|r\| r.shuffle(slice))
140	0	}
141
142		/// Fill a byte slice with random data.
143		#[inline]
144	0	pub fn fill(slice: &mut [u8]) {
145	0	with_rng(\|r\| r.fill(slice))
146	0	}
147
148		macro_rules! integer {
149		($t:tt, $doc:tt) => {
150		#[doc = $doc]
151		///
152		/// Panics if the range is empty.
153		#[inline]
154	0	pub fn $t(range: impl RangeBounds<$t>) -> $t {
155	0	with_rng(\|r\| r.$t(range)) Unexecuted instantiation: fastrand::global_rng::i8::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::u8::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::i16::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::i32::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::i64::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::u16::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::u32::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::u64::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::char::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::i128::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::u128::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::isize::<_>::{closure#0} Unexecuted instantiation: fastrand::global_rng::usize::<_>::{closure#0}
156	0	} Unexecuted instantiation: fastrand::global_rng::i8::<_> Unexecuted instantiation: fastrand::global_rng::u8::<_> Unexecuted instantiation: fastrand::global_rng::i16::<_> Unexecuted instantiation: fastrand::global_rng::i32::<_> Unexecuted instantiation: fastrand::global_rng::i64::<_> Unexecuted instantiation: fastrand::global_rng::u16::<_> Unexecuted instantiation: fastrand::global_rng::u32::<_> Unexecuted instantiation: fastrand::global_rng::u64::<_> Unexecuted instantiation: fastrand::global_rng::char::<_> Unexecuted instantiation: fastrand::global_rng::i128::<_> Unexecuted instantiation: fastrand::global_rng::u128::<_> Unexecuted instantiation: fastrand::global_rng::isize::<_> Unexecuted instantiation: fastrand::global_rng::usize::<_>
157		};
158		}
159
160		integer!(u8, "Generates a random `u8` in the given range.");
161		integer!(i8, "Generates a random `i8` in the given range.");
162		integer!(u16, "Generates a random `u16` in the given range.");
163		integer!(i16, "Generates a random `i16` in the given range.");
164		integer!(u32, "Generates a random `u32` in the given range.");
165		integer!(i32, "Generates a random `i32` in the given range.");
166		integer!(u64, "Generates a random `u64` in the given range.");
167		integer!(i64, "Generates a random `i64` in the given range.");
168		integer!(u128, "Generates a random `u128` in the given range.");
169		integer!(i128, "Generates a random `i128` in the given range.");
170		integer!(usize, "Generates a random `usize` in the given range.");
171		integer!(isize, "Generates a random `isize` in the given range.");
172		integer!(char, "Generates a random `char` in the given range.");
173
174		/// Generates a random `f32` in range `0..1`.
175	0	pub fn f32() -> f32 {
176	0	with_rng(\|r\| r.f32())
177	0	}
178
179		/// Generates a random `f64` in range `0..1`.
180	0	pub fn f64() -> f64 {
181	0	with_rng(\|r\| r.f64())
182	0	}
183
184		/// Collects `amount` values at random from the iterable into a vector.
185	0	pub fn choose_multiple<I: IntoIterator>(source: I, amount: usize) -> Vec<I::Item> {
186	0	with_rng(\|rng\| rng.choose_multiple(source, amount))
187	0	}
188
189		#[cfg(not(all(
190		any(target_arch = "wasm32", target_arch = "wasm64"),
191		target_os = "unknown"
192		)))]
193	0	fn random_seed() -> Option<u64> {
194		use std::collections::hash_map::DefaultHasher;
195		use std::hash::{Hash, Hasher};
196		use std::thread;
197		use std::time::Instant;
198
199	0	let mut hasher = DefaultHasher::new();
200	0	Instant::now().hash(&mut hasher);
201	0	thread::current().id().hash(&mut hasher);
202	0	Some(hasher.finish())
203	0	}
204
205		#[cfg(all(
206		any(target_arch = "wasm32", target_arch = "wasm64"),
207		target_os = "unknown",
208		feature = "js"
209		))]
210		fn random_seed() -> Option<u64> {
211		// TODO(notgull): Failures should be logged somewhere.
212		let mut seed = [0u8; 8];
213		getrandom::getrandom(&mut seed).ok()?;
214		Some(u64::from_ne_bytes(seed))
215		}
216
217		#[cfg(all(
218		any(target_arch = "wasm32", target_arch = "wasm64"),
219		target_os = "unknown",
220		not(feature = "js")
221		))]
222		fn random_seed() -> Option<u64> {
223		None
224		}