18145139209

Committed 30 Sep 2025 10:26PM UTC coverage: 43.572% (-5.2%) from 48.731%

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vigna

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Unified test

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70.0

/src/codes/minimal_binary.rs

/*
 * SPDX-FileCopyrightText: 2023 Tommaso Fontana
 * SPDX-FileCopyrightText: 2023 Inria
 * SPDX-FileCopyrightText: 2023 Sebastiano Vigna
 *
 * SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
 */

//! Minimal binary codes.
//!
//! A minimal binary code with upper bound *u* > 0 (AKA [truncated binary
//! encoding](https://en.wikipedia.org/wiki/Truncated_binary_encoding)) is an
//! optimal prefix-free code for the first *u* natural numbers with uniform
//! distribution.
//!
//! There are several such codes, and the one implemented here is defined as
//! follows: let *s* = ⌈log₂*u*⌉; then, given *x* < *u*, if *x* <
//! 2*ˢ* − *u* then *x* is coded as the binary representation of *x*
//! in *s* − 1 bits; otherwise, *x* is coded as the binary representation of *x*
//! − *u* + 2*ˢ* in *s* bits.
//!
//! The supported range for *u* is [0 . . 2⁶⁴).
//!
//! See the [codes module documentation](crate::codes) for some elaboration on
//! the difference between the big-endian and little-endian versions of the
//! codes.

use crate::traits::*;

/// Returns the length of the minimal binary code for `n` with upper bound `u`.
#[must_use]
#[inline(always)]
pub fn len_minimal_binary(n: u64, u: u64) -> usize {
    debug_assert!(n < u);
    if u == 0 {
        return 0;
    }
    let l = u.ilog2();
    let limit = ((1_u64 << l) << 1).wrapping_sub(u);
    let mut result = l as usize;
    if n >= limit {
        result += 1;
    }
    result
}

/// Trait for reading minimal binary codes.
pub trait MinimalBinaryRead<E: Endianness>: BitRead<E> {
    #[inline(always)]
    fn read_minimal_binary(&mut self, u: u64) -> Result<u64, Self::Error> {
        let l = u.ilog2();
        let mut prefix = self.read_bits(l as _)?;
        let limit = ((1_u64 << l) << 1).wrapping_sub(u);

        Ok(if prefix < limit {
            prefix
        } else {
            prefix <<= 1;
            prefix |= self.read_bits(1)?;
            prefix - limit
        })
    }
}

/// Trait for writing minimal binary codes.
pub trait MinimalBinaryWrite<E: Endianness>: BitWrite<E> {
    #[inline(always)]
    fn write_minimal_binary(&mut self, n: u64, u: u64) -> Result<usize, Self::Error> {
        debug_assert!(n < u);
        let l = u.ilog2();
        let limit = ((1_u64 << l) << 1).wrapping_sub(u);

        if n < limit {
            self.write_bits(n, l as _)?;
            Ok(l as usize)
        } else {
            let to_write = n + limit;
            self.write_bits(to_write >> 1, l as _)?;
            self.write_bits(to_write & 1, 1)?;
            Ok((l + 1) as usize)
        }
    }
}

impl<E: Endianness, B: BitRead<E>> MinimalBinaryRead<E> for B {}
impl<E: Endianness, B: BitWrite<E>> MinimalBinaryWrite<E> for B {}

1	/*
2	* SPDX-FileCopyrightText: 2023 Tommaso Fontana
3	* SPDX-FileCopyrightText: 2023 Inria
4	* SPDX-FileCopyrightText: 2023 Sebastiano Vigna
5	*
6	* SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
7	*/
8
9	//! Minimal binary codes.
10	//!
11	//! A minimal binary code with upper bound u > 0 (AKA [truncated binary
12	//! encoding](https://en.wikipedia.org/wiki/Truncated_binary_encoding)) is an
13	//! optimal prefix-free code for the first u natural numbers with uniform
14	//! distribution.
15	//!
16	//! There are several such codes, and the one implemented here is defined as
17	//! follows: let s = ⌈log₂u⌉; then, given x < u, if x <
18	//! 2ˢ − u then x is coded as the binary representation of x
19	//! in s − 1 bits; otherwise, x is coded as the binary representation of x
20	//! − u + 2ˢ in s bits.
21	//!
22	//! The supported range for u is [0 . . 2⁶⁴).
23	//!
24	//! See the [codes module documentation](crate::codes) for some elaboration on
25	//! the difference between the big-endian and little-endian versions of the
26	//! codes.
27
28	use crate::traits::*;
29
30	/// Returns the length of the minimal binary code for `n` with upper bound `u`.
31	#[must_use]
32	#[inline(always)]
33	pub fn len_minimal_binary(n: u64, u: u64) -> usize {	6,743✔
34	debug_assert!(n < u);	13,486✔
35	if u == 0 {	6,743✔
36	return 0;	×
37	}
UNCOV 38	let l = u.ilog2();	×
UNCOV 39	let limit = ((1_u64 << l) << 1).wrapping_sub(u);	×
40	let mut result = l as usize;	×
41	if n >= limit {	5,275✔
42	result += 1;	5,275✔
43	}
UNCOV 44	result	×
45	}
46
47	/// Trait for reading minimal binary codes.
48	pub trait MinimalBinaryRead<E: Endianness>: BitRead<E> {
49	#[inline(always)]
50	fn read_minimal_binary(&mut self, u: u64) -> Result<u64, Self::Error> {	76,057✔
51	let l = u.ilog2();	228,171✔
52	let mut prefix = self.read_bits(l as _)?;	304,228✔
UNCOV 53	let limit = ((1_u64 << l) << 1).wrapping_sub(u);	×
54
UNCOV 55	Ok(if prefix < limit {	×
56	prefix	38,745✔
57	} else {
58	prefix <<= 1;	37,312✔
UNCOV 59	prefix \|= self.read_bits(1)?;	×
60	prefix - limit	37,312✔
61	})
62	}
63	}
64
65	/// Trait for writing minimal binary codes.
66	pub trait MinimalBinaryWrite<E: Endianness>: BitWrite<E> {
67	#[inline(always)]
68	fn write_minimal_binary(&mut self, n: u64, u: u64) -> Result<usize, Self::Error> {	68,962✔
69	debug_assert!(n < u);	137,924✔
70	let l = u.ilog2();	206,886✔
71	let limit = ((1_u64 << l) << 1).wrapping_sub(u);	275,848✔
72
73	if n < limit {	68,962✔
74	self.write_bits(n, l as _)?;	130,320✔
75	Ok(l as usize)	32,580✔
76	} else {
77	let to_write = n + limit;	36,382✔
UNCOV 78	self.write_bits(to_write >> 1, l as _)?;	×
79	self.write_bits(to_write & 1, 1)?;	36,382✔
80	Ok((l + 1) as usize)	36,382✔
81	}
82	}
83	}
84
85	impl<E: Endianness, B: BitRead<E>> MinimalBinaryRead<E> for B {}
86	impl<E: Endianness, B: BitWrite<E>> MinimalBinaryWrite<E> for B {}

vigna / dsi-bitstream-rs / 18145139209

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