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532ac7d7 XL |
1 | //! Arithmetic on **Iterator** *.size_hint()* values. |
2 | //! | |
3 | ||
4 | use std::usize; | |
5 | use std::cmp; | |
6 | ||
7 | /// **SizeHint** is the return type of **Iterator::size_hint()**. | |
8 | pub type SizeHint = (usize, Option<usize>); | |
9 | ||
10 | /// Add **SizeHint** correctly. | |
11 | #[inline] | |
12 | pub fn add(a: SizeHint, b: SizeHint) -> SizeHint { | |
13 | let min = a.0.checked_add(b.0).unwrap_or(usize::MAX); | |
14 | let max = match (a.1, b.1) { | |
15 | (Some(x), Some(y)) => x.checked_add(y), | |
16 | _ => None, | |
17 | }; | |
18 | ||
19 | (min, max) | |
20 | } | |
21 | ||
22 | /// Add **x** correctly to a **SizeHint**. | |
23 | #[inline] | |
24 | pub fn add_scalar(sh: SizeHint, x: usize) -> SizeHint { | |
25 | let (mut low, mut hi) = sh; | |
26 | low = low.saturating_add(x); | |
27 | hi = hi.and_then(|elt| elt.checked_add(x)); | |
28 | (low, hi) | |
29 | } | |
30 | ||
31 | /// Sbb **x** correctly to a **SizeHint**. | |
32 | #[inline] | |
33 | #[allow(dead_code)] | |
34 | pub fn sub_scalar(sh: SizeHint, x: usize) -> SizeHint { | |
35 | let (mut low, mut hi) = sh; | |
36 | low = low.saturating_sub(x); | |
37 | hi = hi.map(|elt| elt.saturating_sub(x)); | |
38 | (low, hi) | |
39 | } | |
40 | ||
41 | ||
42 | /// Multiply **SizeHint** correctly | |
43 | /// | |
44 | /// ```ignore | |
45 | /// use std::usize; | |
46 | /// use itertools::size_hint; | |
47 | /// | |
48 | /// assert_eq!(size_hint::mul((3, Some(4)), (3, Some(4))), | |
49 | /// (9, Some(16))); | |
50 | /// | |
51 | /// assert_eq!(size_hint::mul((3, Some(4)), (usize::MAX, None)), | |
52 | /// (usize::MAX, None)); | |
53 | /// | |
54 | /// assert_eq!(size_hint::mul((3, None), (0, Some(0))), | |
55 | /// (0, Some(0))); | |
56 | /// ``` | |
57 | #[inline] | |
58 | pub fn mul(a: SizeHint, b: SizeHint) -> SizeHint { | |
59 | let low = a.0.checked_mul(b.0).unwrap_or(usize::MAX); | |
60 | let hi = match (a.1, b.1) { | |
61 | (Some(x), Some(y)) => x.checked_mul(y), | |
62 | (Some(0), None) | (None, Some(0)) => Some(0), | |
63 | _ => None, | |
64 | }; | |
65 | (low, hi) | |
66 | } | |
67 | ||
68 | /// Multiply **x** correctly with a **SizeHint**. | |
69 | #[inline] | |
70 | pub fn mul_scalar(sh: SizeHint, x: usize) -> SizeHint { | |
71 | let (mut low, mut hi) = sh; | |
72 | low = low.saturating_mul(x); | |
73 | hi = hi.and_then(|elt| elt.checked_mul(x)); | |
74 | (low, hi) | |
75 | } | |
76 | ||
77 | /// Return the maximum | |
78 | #[inline] | |
79 | pub fn max(a: SizeHint, b: SizeHint) -> SizeHint { | |
80 | let (a_lower, a_upper) = a; | |
81 | let (b_lower, b_upper) = b; | |
82 | ||
83 | let lower = cmp::max(a_lower, b_lower); | |
84 | ||
85 | let upper = match (a_upper, b_upper) { | |
86 | (Some(x), Some(y)) => Some(cmp::max(x, y)), | |
87 | _ => None, | |
88 | }; | |
89 | ||
90 | (lower, upper) | |
91 | } | |
92 | ||
93 | /// Return the minimum | |
94 | #[inline] | |
95 | pub fn min(a: SizeHint, b: SizeHint) -> SizeHint { | |
96 | let (a_lower, a_upper) = a; | |
97 | let (b_lower, b_upper) = b; | |
98 | let lower = cmp::min(a_lower, b_lower); | |
99 | let upper = match (a_upper, b_upper) { | |
100 | (Some(u1), Some(u2)) => Some(cmp::min(u1, u2)), | |
101 | _ => a_upper.or(b_upper), | |
102 | }; | |
103 | (lower, upper) | |
104 | } |