itertools/
size_hint.rs

1//! Arithmetic on `Iterator.size_hint()` values.
2//!
3
4use std::usize;
5use std::cmp;
6use std::u32;
7
8/// `SizeHint` is the return type of `Iterator::size_hint()`.
9pub type SizeHint = (usize, Option<usize>);
10
11/// Add `SizeHint` correctly.
12#[inline]
13pub fn add(a: SizeHint, b: SizeHint) -> SizeHint {
14    let min = a.0.saturating_add(b.0);
15    let max = match (a.1, b.1) {
16        (Some(x), Some(y)) => x.checked_add(y),
17        _ => None,
18    };
19
20    (min, max)
21}
22
23/// Add `x` correctly to a `SizeHint`.
24#[inline]
25pub fn add_scalar(sh: SizeHint, x: usize) -> SizeHint {
26    let (mut low, mut hi) = sh;
27    low = low.saturating_add(x);
28    hi = hi.and_then(|elt| elt.checked_add(x));
29    (low, hi)
30}
31
32/// Subtract `x` correctly from a `SizeHint`.
33#[inline]
34#[allow(dead_code)]
35pub fn sub_scalar(sh: SizeHint, x: usize) -> SizeHint {
36    let (mut low, mut hi) = sh;
37    low = low.saturating_sub(x);
38    hi = hi.map(|elt| elt.saturating_sub(x));
39    (low, hi)
40}
41
42
43/// Multiply `SizeHint` correctly
44///
45/// ```ignore
46/// use std::usize;
47/// use itertools::size_hint;
48///
49/// assert_eq!(size_hint::mul((3, Some(4)), (3, Some(4))),
50///            (9, Some(16)));
51///
52/// assert_eq!(size_hint::mul((3, Some(4)), (usize::MAX, None)),
53///            (usize::MAX, None));
54///
55/// assert_eq!(size_hint::mul((3, None), (0, Some(0))),
56///            (0, Some(0)));
57/// ```
58#[inline]
59pub fn mul(a: SizeHint, b: SizeHint) -> SizeHint {
60    let low = a.0.saturating_mul(b.0);
61    let hi = match (a.1, b.1) {
62        (Some(x), Some(y)) => x.checked_mul(y),
63        (Some(0), None) | (None, Some(0)) => Some(0),
64        _ => None,
65    };
66    (low, hi)
67}
68
69/// Multiply `x` correctly with a `SizeHint`.
70#[inline]
71pub fn mul_scalar(sh: SizeHint, x: usize) -> SizeHint {
72    let (mut low, mut hi) = sh;
73    low = low.saturating_mul(x);
74    hi = hi.and_then(|elt| elt.checked_mul(x));
75    (low, hi)
76}
77
78/// Raise `base` correctly by a `SizeHint` exponent.
79#[inline]
80pub fn pow_scalar_base(base: usize, exp: SizeHint) -> SizeHint {
81    let exp_low = cmp::min(exp.0, u32::MAX as usize) as u32;
82    let low = base.saturating_pow(exp_low);
83
84    let hi = exp.1.and_then(|exp| {
85        let exp_hi = cmp::min(exp, u32::MAX as usize) as u32;
86        base.checked_pow(exp_hi)
87    });
88
89    (low, hi)
90}
91
92/// Return the maximum
93#[inline]
94pub fn max(a: SizeHint, b: SizeHint) -> SizeHint {
95    let (a_lower, a_upper) = a;
96    let (b_lower, b_upper) = b;
97
98    let lower = cmp::max(a_lower, b_lower);
99
100    let upper = match (a_upper, b_upper) {
101        (Some(x), Some(y)) => Some(cmp::max(x, y)),
102        _ => None,
103    };
104
105    (lower, upper)
106}
107
108/// Return the minimum
109#[inline]
110pub fn min(a: SizeHint, b: SizeHint) -> SizeHint {
111    let (a_lower, a_upper) = a;
112    let (b_lower, b_upper) = b;
113    let lower = cmp::min(a_lower, b_lower);
114    let upper = match (a_upper, b_upper) {
115        (Some(u1), Some(u2)) => Some(cmp::min(u1, u2)),
116        _ => a_upper.or(b_upper),
117    };
118    (lower, upper)
119}
itertools/size_hint.rs

itertools/
size_hint.rs
