18131186772

Committed 30 Sep 2025 01:16PM UTC coverage: 48.731% (-3.0%) from 51.712%

Build # 18131186772

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push

github

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vigna

Commit Message

Better error message

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67.86

/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.
//!
//! 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 `max`.
#[must_use]
#[inline(always)]
pub fn len_minimal_binary(n: u64, max: u64) -> usize {
    if max == 0 {
        return 0;
    }
    let l = max.ilog2();
    let limit = ((1_u64 << l) << 1).wrapping_sub(max);
    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, max: u64) -> Result<u64, Self::Error> {
        let l = max.ilog2();
        let mut prefix = self.read_bits(l as _)?;
        let limit = ((1_u64 << l) << 1).wrapping_sub(max);

        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, max: u64) -> Result<usize, Self::Error> {
        let l = max.ilog2();
        let limit = ((1_u64 << l) << 1).wrapping_sub(max);

        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	//! See the [codes module documentation](crate::codes) for some elaboration on
23	//! the difference between the big-endian and little-endian versions of the
24	//! codes.
25
26	use crate::traits::*;
27
28	/// Returns the length of the minimal binary code for `n` with upper bound `max`.
29	#[must_use]
30	#[inline(always)]
31	pub fn len_minimal_binary(n: u64, max: u64) -> usize {	71,929✔
32	if max == 0 {	71,929✔
33	return 0;	×
34	}
UNCOV 35	let l = max.ilog2();	×
UNCOV 36	let limit = ((1_u64 << l) << 1).wrapping_sub(max);	×
UNCOV 37	let mut result = l as usize;	×
38	if n >= limit {	39,264✔
39	result += 1;	39,264✔
40	}
41	result	×
42	}
43
44	/// Trait for reading minimal binary codes.
45	pub trait MinimalBinaryRead<E: Endianness>: BitRead<E> {
46	#[inline(always)]
47	fn read_minimal_binary(&mut self, max: u64) -> Result<u64, Self::Error> {	39,003✔
48	let l = max.ilog2();	117,009✔
49	let mut prefix = self.read_bits(l as _)?;	156,012✔
50	let limit = ((1_u64 << l) << 1).wrapping_sub(max);	×
51
52	Ok(if prefix < limit {	×
53	prefix	19,383✔
54	} else {
55	prefix <<= 1;	19,620✔
UNCOV 56	prefix \|= self.read_bits(1)?;	×
57	prefix - limit	19,620✔
58	})
59	}
60	}
61
62	/// Trait for writing minimal binary codes.
63	pub trait MinimalBinaryWrite<E: Endianness>: BitWrite<E> {
64	#[inline(always)]
65	fn write_minimal_binary(&mut self, n: u64, max: u64) -> Result<usize, Self::Error> {	35,114✔
66	let l = max.ilog2();	105,342✔
67	let limit = ((1_u64 << l) << 1).wrapping_sub(max);	140,456✔
68
69	if n < limit {	35,114✔
70	self.write_bits(n, l as _)?;	65,688✔
71	Ok(l as usize)	16,422✔
72	} else {
73	let to_write = n + limit;	18,692✔
UNCOV 74	self.write_bits(to_write >> 1, l as _)?;	×
75	self.write_bits(to_write & 1, 1)?;	18,692✔
76	Ok((l + 1) as usize)	18,692✔
77	}
78	}
79	}
80
81	impl<E: Endianness, B: BitRead<E>> MinimalBinaryRead<E> for B {}
82	impl<E: Endianness, B: BitWrite<E>> MinimalBinaryWrite<E> for B {}

vigna / dsi-bitstream-rs / 18131186772

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