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// Copyright © 2026 Mikhail Hogrefe
//
// Uses code adopted from the FLINT Library.
//
// Copyright © 2010 William Hart
//
// Copyright © 2021 Fredrik Johansson
//
// This file is part of Malachite.
//
// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
use crate::num::arithmetic::traits::ModSum;
use crate::num::basic::unsigneds::PrimitiveUnsigned;
fn mod_sum<T: PrimitiveUnsigned, I: Iterator<Item = T>>(xs: I, m: T) -> T {
assert_ne!(m, T::ZERO, "m cannot be zero");
xs.fold(T::ZERO, |s, x| {
assert!(x < m, "x must be reduced mod m, but {x} >= {m}");
s.mod_add(x, m)
})
}
macro_rules! impl_mod_sum {
($t:ident) => {
impl ModSum for $t {
/// Adds up all the numbers in an iterator, modulo another number $m$. Every number must
/// be already reduced modulo $m$.
///
/// $f((x_i)_ {i=0}^{n-1}, m) = y$, where $y < m$ and $\sum_ {i=0}^{n-1} x_i \equiv y
/// \mod m$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `xs.count()`.
///
/// # Panics
/// Panics if `m` is zero or if any number is greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_sum#mod_sum).
#[inline]
fn mod_sum<I: Iterator<Item = $t>>(xs: I, m: $t) -> $t {
mod_sum(xs, m)
}
}
impl<'a> ModSum<&'a $t, $t> for $t {
/// Adds up all the numbers in an iterator of references, modulo another number $m$.
/// Every number must be already reduced modulo $m$.
///
/// $f((x_i)_ {i=0}^{n-1}, m) = y$, where $y < m$ and $\sum_ {i=0}^{n-1} x_i \equiv y
/// \mod m$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `xs.count()`.
///
/// # Panics
/// Panics if `m` is zero or if any number is greater than or equal to `m`.
///
/// # Examples
/// See [here](super::mod_sum#mod_sum).
#[inline]
fn mod_sum<I: Iterator<Item = &'a $t>>(xs: I, m: $t) -> $t {
mod_sum(xs.copied(), m)
}
}
};
}
apply_to_unsigneds!(impl_mod_sum);