Remove custom doubling strategy + add examples to VecAllocEx
#9058
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| /// // push more data into the vec | ||
| /// for _ in 0..10 { vec.push_accounted(1, &mut allocated); } | ||
| /// assert_eq!(allocated, 64); // underlying vec has space for 10 u32s | ||
| /// assert_eq!(vec.allocated_size(), 64); |
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The allocated size was different than what was obtained by push_accounted prior to this change
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| // growth factor: 2, but at least 2 elements | ||
| let bump_elements = (self.capacity() * 2).max(2); | ||
| let bump_size = std::mem::size_of::<u32>() * bump_elements; |
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I think this should be sizeof<T> rather than sizeof<u32> but perhaps I am missing something
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looks correct. I suspect this was the cause of the discrepancy in the original code
alamb
changed the title
VecAllocEx
| let new_capacity = self.capacity(); | ||
| if new_capacity > prev_capacty { | ||
| // capacity changed, so we allocated more | ||
| let bump_size = (new_capacity - prev_capacty) * std::mem::size_of::<T>(); |
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does it make sense to do a checked_mul here similar to the checked_add below?
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either that or remove the checked_add because push would panic first now that it's called first instead of at the end
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thinking about it more: if accounting is tracking multiple vecs, then this makes sense. multiplication should never overflow because push would panic first in that case, but the checked_add could potentially overflow since accounting could be some value greater than capacity.
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I think that is a good point. I will add a comment to clarify
| let new_capacity = self.capacity(); | ||
| if new_capacity > prev_capacty { | ||
| // capacity changed, so we allocated more | ||
| let bump_size = (new_capacity - prev_capacty) * std::mem::size_of::<T>(); |
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I think that is a good point. I will add a comment to clarify
Which issue does this PR close?
Closes #9057
Rationale for this change
While writing documentation as suggested by @crepererum on #9025 (comment) I found that the accounting with
push_accountedandallocated_sizewere different and inconsistentWhat changes are included in this PR?
Are these changes tested?
Yes, with doc tests
Are there any user-facing changes?
Allocation accounting is now different