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Improve size_hint bounds for DecodeUtf16 iterator #88763

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Improve size_hint bounds for DecodeUtf16 iterator #88763

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bea5cd1
Improve `size_hint` lower bound for `DecodeUtf16` iterator
steffahn Sep 8, 2021
fa5e283
Add comments, and fix issue 88762
steffahn Sep 8, 2021
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7 changes: 6 additions & 1 deletion library/core/src/char/decode.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -122,7 +122,12 @@ impl<I: Iterator<Item = u16>> Iterator for DecodeUtf16<I> {
let (low, high) = self.iter.size_hint();
// we could be entirely valid surrogates (2 elements per
// char), or entirely non-surrogates (1 element per char)
(low / 2, high)
//
// In addition to `self.iter`, there's potentially one
// additional number in `self.buf`.
// On odd lower bound, at least one element must stay unpaired
// (with other elements from `self.iter`).
(low.div_ceil(2), try { high?.checked_add(1)? })
}
}

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