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Diffstat (limited to 'src/size_hint.rs')
-rw-r--r-- | src/size_hint.rs | 104 |
1 files changed, 104 insertions, 0 deletions
diff --git a/src/size_hint.rs b/src/size_hint.rs new file mode 100644 index 0000000..be54443 --- /dev/null +++ b/src/size_hint.rs @@ -0,0 +1,104 @@ +//! Arithmetic on **Iterator** *.size_hint()* values. +//! + +use std::usize; +use std::cmp; + +/// **SizeHint** is the return type of **Iterator::size_hint()**. +pub type SizeHint = (usize, Option<usize>); + +/// Add **SizeHint** correctly. +#[inline] +pub fn add(a: SizeHint, b: SizeHint) -> SizeHint { + let min = a.0.checked_add(b.0).unwrap_or(usize::MAX); + let max = match (a.1, b.1) { + (Some(x), Some(y)) => x.checked_add(y), + _ => None, + }; + + (min, max) +} + +/// Add **x** correctly to a **SizeHint**. +#[inline] +pub fn add_scalar(sh: SizeHint, x: usize) -> SizeHint { + let (mut low, mut hi) = sh; + low = low.saturating_add(x); + hi = hi.and_then(|elt| elt.checked_add(x)); + (low, hi) +} + +/// Sbb **x** correctly to a **SizeHint**. +#[inline] +#[allow(dead_code)] +pub fn sub_scalar(sh: SizeHint, x: usize) -> SizeHint { + let (mut low, mut hi) = sh; + low = low.saturating_sub(x); + hi = hi.map(|elt| elt.saturating_sub(x)); + (low, hi) +} + + +/// Multiply **SizeHint** correctly +/// +/// ```ignore +/// use std::usize; +/// use itertools::size_hint; +/// +/// assert_eq!(size_hint::mul((3, Some(4)), (3, Some(4))), +/// (9, Some(16))); +/// +/// assert_eq!(size_hint::mul((3, Some(4)), (usize::MAX, None)), +/// (usize::MAX, None)); +/// +/// assert_eq!(size_hint::mul((3, None), (0, Some(0))), +/// (0, Some(0))); +/// ``` +#[inline] +pub fn mul(a: SizeHint, b: SizeHint) -> SizeHint { + let low = a.0.checked_mul(b.0).unwrap_or(usize::MAX); + let hi = match (a.1, b.1) { + (Some(x), Some(y)) => x.checked_mul(y), + (Some(0), None) | (None, Some(0)) => Some(0), + _ => None, + }; + (low, hi) +} + +/// Multiply **x** correctly with a **SizeHint**. +#[inline] +pub fn mul_scalar(sh: SizeHint, x: usize) -> SizeHint { + let (mut low, mut hi) = sh; + low = low.saturating_mul(x); + hi = hi.and_then(|elt| elt.checked_mul(x)); + (low, hi) +} + +/// Return the maximum +#[inline] +pub fn max(a: SizeHint, b: SizeHint) -> SizeHint { + let (a_lower, a_upper) = a; + let (b_lower, b_upper) = b; + + let lower = cmp::max(a_lower, b_lower); + + let upper = match (a_upper, b_upper) { + (Some(x), Some(y)) => Some(cmp::max(x, y)), + _ => None, + }; + + (lower, upper) +} + +/// Return the minimum +#[inline] +pub fn min(a: SizeHint, b: SizeHint) -> SizeHint { + let (a_lower, a_upper) = a; + let (b_lower, b_upper) = b; + let lower = cmp::min(a_lower, b_lower); + let upper = match (a_upper, b_upper) { + (Some(u1), Some(u2)) => Some(cmp::min(u1, u2)), + _ => a_upper.or(b_upper), + }; + (lower, upper) +} |