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use crate::lib::*;
pub fn from_bounds<I>(iter: &I) -> Option<usize>
where
I: Iterator,
{
helper(iter.size_hint())
}
#[cfg(any(feature = "std", feature = "alloc"))]
pub fn cautious<Element>(hint: Option<usize>) -> usize {
const MAX_PREALLOC_BYTES: usize = 1024 * 1024;
if mem::size_of::<Element>() == 0 {
0
} else {
cmp::min(
hint.unwrap_or(0),
MAX_PREALLOC_BYTES / mem::size_of::<Element>(),
)
}
}
fn helper(bounds: (usize, Option<usize>)) -> Option<usize> {
match bounds {
(lower, Some(upper)) if lower == upper => Some(upper),
_ => None,
}
}