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Implement useful steps_between for all integers

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We can use `usize::try_from` to convert steps from any size of integer.
This enables a meaningful `size_hint()` for larger ranges, rather than
always just `(0, None)`. Now they return the true `(len, Some(len))`
when it fits, otherwise `(usize::MAX, None)` for overflow.
This commit is contained in:
Josh Stone 2019-03-25 21:12:53 -07:00
parent d91b32b4dc
commit 01162d86c5
2 changed files with 57 additions and 49 deletions
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57
src/libcore/iter/range.rs
View File

@ -68,11 +68,9 @@ macro_rules! step_impl_unsigned {
issue = "42168")]
impl Step for $t {
#[inline]
#[allow(trivial_numeric_casts)]
fn steps_between(start: &$t, end: &$t) -> Option<usize> {
if *start < *end {
// Note: We assume $t <= usize here
Some((*end - *start) as usize)
usize::try_from(*end - *start).ok()
} else {
Some(0)
}
@ -98,13 +96,11 @@ macro_rules! step_impl_signed {
issue = "42168")]
impl Step for $t {
#[inline]
#[allow(trivial_numeric_casts)]
fn steps_between(start: &$t, end: &$t) -> Option<usize> {
if *start < *end {
// Note: We assume $t <= isize here
// Use .wrapping_sub and cast to usize to compute the
// difference that may not fit inside the range of isize.
Some((*end as isize).wrapping_sub(*start as isize) as usize)
// Use .wrapping_sub and cast to unsigned to compute the
// difference that may not fit inside the range of $t.
usize::try_from(end.wrapping_sub(*start) as $unsigned).ok()
} else {
Some(0)
}
@ -134,46 +130,9 @@ fn add_usize(&self, n: usize) -> Option<Self> {
)*)
}
macro_rules! step_impl_no_between {
($($t:ty)*) => ($(
#[unstable(feature = "step_trait",
reason = "likely to be replaced by finer-grained traits",
issue = "42168")]
impl Step for $t {
#[inline]
fn steps_between(_start: &Self, _end: &Self) -> Option<usize> {
None
}
#[inline]
fn add_usize(&self, n: usize) -> Option<Self> {
self.checked_add(n as $t)
}
step_identical_methods!();
}
)*)
}
step_impl_unsigned!(usize u8 u16);
#[cfg(not(target_pointer_width = "16"))]
step_impl_unsigned!(u32);
#[cfg(target_pointer_width = "16")]
step_impl_no_between!(u32);
step_impl_unsigned!(usize u8 u16 u32 u64 u128);
step_impl_signed!([isize: usize] [i8: u8] [i16: u16]);
#[cfg(not(target_pointer_width = "16"))]
step_impl_signed!([i32: u32]);
#[cfg(target_pointer_width = "16")]
step_impl_no_between!(i32);
#[cfg(target_pointer_width = "64")]
step_impl_unsigned!(u64);
#[cfg(target_pointer_width = "64")]
step_impl_signed!([i64: u64]);
// If the target pointer width is not 64-bits, we
// assume here that it is less than 64-bits.
#[cfg(not(target_pointer_width = "64"))]
step_impl_no_between!(u64 i64);
step_impl_no_between!(u128 i128);
step_impl_signed!([i32: u32] [i64: u64] [i128: u128]);
macro_rules! range_exact_iter_impl {
($($t:ty)*) => ($(
@ -229,7 +188,7 @@ fn next(&mut self) -> Option<A> {
fn size_hint(&self) -> (usize, Option<usize>) {
match Step::steps_between(&self.start, &self.end) {
Some(hint) => (hint, Some(hint)),
None => (0, None)
None => (usize::MAX, None)
}
}
@ -350,7 +309,7 @@ fn size_hint(&self) -> (usize, Option<usize>) {
match Step::steps_between(&self.start, &self.end) {
Some(hint) => (hint.saturating_add(1), hint.checked_add(1)),
None => (0, None),
None => (usize::MAX, None),
}
}

49
src/libcore/tests/iter.rs
View File

@ -1,4 +1,5 @@
use core::cell::Cell;
use core::convert::TryFrom;
use core::iter::*;
use core::{i8, i16, isize};
use core::usize;
@ -1800,6 +1801,54 @@ fn test_range_inclusive_folds() {
assert!(it.is_empty());
}
#[test]
fn test_range_size_hint() {
use core::usize::MAX as UMAX;
assert_eq!((0..100usize).size_hint(), (100, Some(100)));
assert_eq!((0..UMAX).size_hint(), (UMAX, Some(UMAX)));
let umax = u128::try_from(UMAX).unwrap();
assert_eq!((0..100u128).size_hint(), (100, Some(100)));
assert_eq!((0..umax).size_hint(), (UMAX, Some(UMAX)));
assert_eq!((0..umax + 1).size_hint(), (UMAX, None));
use core::isize::{MAX as IMAX, MIN as IMIN};
assert_eq!((-100..100isize).size_hint(), (200, Some(200)));
assert_eq!((IMIN..IMAX).size_hint(), (UMAX, Some(UMAX)));
let imin = i128::try_from(IMIN).unwrap();
let imax = i128::try_from(IMAX).unwrap();
assert_eq!((-100..100i128).size_hint(), (200, Some(200)));
assert_eq!((imin..imax).size_hint(), (UMAX, Some(UMAX)));
assert_eq!((imin..imax + 1).size_hint(), (UMAX, None));
}
#[test]
fn test_range_inclusive_size_hint() {
use core::usize::MAX as UMAX;
assert_eq!((0..=100usize).size_hint(), (101, Some(101)));
assert_eq!((0..=UMAX - 1).size_hint(), (UMAX, Some(UMAX)));
assert_eq!((0..=UMAX).size_hint(), (UMAX, None));
let umax = u128::try_from(UMAX).unwrap();
assert_eq!((0..=100u128).size_hint(), (101, Some(101)));
assert_eq!((0..=umax - 1).size_hint(), (UMAX, Some(UMAX)));
assert_eq!((0..=umax).size_hint(), (UMAX, None));
assert_eq!((0..=umax + 1).size_hint(), (UMAX, None));
use core::isize::{MAX as IMAX, MIN as IMIN};
assert_eq!((-100..=100isize).size_hint(), (201, Some(201)));
assert_eq!((IMIN..=IMAX - 1).size_hint(), (UMAX, Some(UMAX)));
assert_eq!((IMIN..=IMAX).size_hint(), (UMAX, None));
let imin = i128::try_from(IMIN).unwrap();
let imax = i128::try_from(IMAX).unwrap();
assert_eq!((-100..=100i128).size_hint(), (201, Some(201)));
assert_eq!((imin..=imax - 1).size_hint(), (UMAX, Some(UMAX)));
assert_eq!((imin..=imax).size_hint(), (UMAX, None));
assert_eq!((imin..=imax + 1).size_hint(), (UMAX, None));
}
#[test]
fn test_repeat() {
let mut it = repeat(42);