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

//! Exponential Golomb codes.
//!
//! Exponential Golomb codes are a variant of Golomb codes with power-of-2
//! modulus (i.e., [Rice codes](super::rice)) in which the prefix is written
//! using [Elias γ code](super::gamma) instead of unary code. More precisely,
//! the exponential Golomb code with parameter `k` of an integer `n` is given
//! `⌊x / 2^k⌋` in [γ code](super::gamma) followed by `x mod 2^k` as  a `k`-bit
//! number. They are used in [H.264
//! (MPEG-4)](https://en.wikipedia.org/wiki/Advanced_Video_Coding) and
//! [H.265](https://en.wikipedia.org/wiki/High_Efficiency_Video_Coding).
//!
//! The exponential Golomb code for `k = 1` is exactly [γ code](super::gamma).

use super::gamma::{len_gamma, GammaRead, GammaWrite};
use crate::traits::*;

/// Return the length of the exponential Golomb code for `n` with parameter `k`.
#[must_use]
#[inline]
pub fn len_exp_golomb(n: u64, k: usize) -> usize {
    len_gamma(n >> k) + k
}

/// Trait for reading exponential Golomb codes.
pub trait ExpGolombRead<E: Endianness>: BitRead<E> + GammaRead<E> {
    #[inline(always)]
    fn read_exp_golomb(&mut self, k: usize) -> Result<u64, Self::Error> {
        Ok((self.read_gamma()? << k) + self.read_bits(k)?)
    }
}

/// Trait for writing exponential Golomb codes.
pub trait ExpGolombWrite<E: Endianness>: BitWrite<E> + GammaWrite<E> {
    #[inline]
    fn write_exp_golomb(&mut self, n: u64, k: usize) -> Result<usize, Self::Error> {
        Ok(self.write_gamma(n >> k)? + self.write_bits(n, k)?)
    }
}

impl<E: Endianness, B: BitRead<E> + GammaRead<E>> ExpGolombRead<E> for B {}
impl<E: Endianness, B: BitWrite<E> + GammaWrite<E>> ExpGolombWrite<E> for B {}