| 1 | use crate::lib::*; |
| 2 | |
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| 3 | pub fn from_bounds<I>(iter: &I) -> Option<usize> |
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| 4 | where |
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| 5 | I: Iterator, |
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| 6 | { |
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| 7 | helper(iter.size_hint()) |
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| 8 | } |
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| 9 | |
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| 10 | #[cfg (any(feature = "std" , feature = "alloc" ))] |
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| 11 | pub fn cautious<Element>(hint: Option<usize>) -> usize { |
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| 12 | const MAX_PREALLOC_BYTES: usize = 1024 * 1024; |
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| 13 | |
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| 14 | if mem::size_of::<Element>() == 0 { |
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| 15 | 0 |
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| 16 | } else { |
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| 17 | cmp::min( |
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| 18 | hint.unwrap_or(0), |
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| 19 | MAX_PREALLOC_BYTES / mem::size_of::<Element>(), |
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| 20 | ) |
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| 21 | } |
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| 22 | } |
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| 23 | |
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| 24 | fn helper(bounds: (usize, Option<usize>)) -> Option<usize> { |
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| 25 | match bounds { |
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| 26 | (lower, Some(upper)) if lower == upper => Some(upper), |
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| 27 | _ => None, |
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| 28 | } |
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| 29 | } |
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| 30 | |
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