perf: Optimize LinearCombination #216
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This was referenced Sep 7, 2021
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vmx
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Sep 23, 2021
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| pub fn iter(&self) -> impl Iterator<Item = (&usize, &T)> + '_ { | ||
| self.values.iter().map(|(key, value)| (key, value)) |
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Question out of interest. Why is the map() needed, why isn't iter() enough?
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because iter gives &(usize, T)
| F: FnOnce() -> T, | ||
| G: FnOnce(&mut T), | ||
| { | ||
| if let Some((last_index, last_key)) = self.last_inserted { |
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It took me a while to understand what's going on. So perhaps a comment would be good. If i understand it correctly the whole if part is an optimization for a case that often happens, which prevents doing a full binary search.
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cryptonemo
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Sep 27, 2021
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The original implementation was using a hashmap, but we only need to store numbers, so we can avoid all hashing. The technique is based on storing sparse matricies and gives overall a speedup of 10-40% in circuit synthesis. The variance comes from the fact that LinearCombination is used in very different sizes and amounts between circuits