Getting started on Huffman tables #441
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Yoric
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| use std::rc::Rc; | ||
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|
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| /// A newtype for `u8` used to count the length of a key in bits. | ||
| #[derive( |
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Long list. Is there a convenient bag of traits which imply all of these?
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Yeah, it's verbose, but I don't know of any such trait.
There used to be something called "int-like", I believe, in another crate, but that crate is now deprecated. I could write a macro, though.
| // Convert tree into bit lengths | ||
| let root = heap.pop().unwrap(); // We have checked above that there is at least one value. | ||
| let mut bit_lengths = Vec::with_capacity(len); | ||
| fn aux<T>(bit_lengths: &mut Vec<(T, BitLen)>, depth: u8, node: NodeContent<T>) { |
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Might be worth putting a FIXME/TODO and an assert here that the length generated is not >20 bits, since this is the earliest you can detect length limits are going to be violated and the code you'll have to change to do limits.
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I thought the idea was to not make the 20 bits part of the spec?
Did I misunderstand #440 (comment) ?
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Added a mechanism to check that we do not exceed a maximal length.
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20 bits is part of the spec; how you compute the number 0 ≤ x ≤ 20 is an
implementation detail.
…On Fri, Sep 13, 2019, 6:38 PM David Teller ***@***.***> wrote:
***@***.**** commented on this pull request.
------------------------------
In crates/binjs_io/src/context/huffman.rs
<#441 (comment)>:
> + // Take the two rarest nodes, merge them behind a prefix,
+ // turn them into a single node with combined number of
+ // instances. Repeat.
+ while heap.len() > 1 {
+ let left = heap.pop().unwrap();
+ let right = heap.pop().unwrap();
+ heap.push(Reverse(Node {
+ instances: left.0.instances + right.0.instances,
+ content: NodeContent::Internal(Rc::new((left.0.content, right.0.content))),
+ }));
+ }
+
+ // Convert tree into bit lengths
+ let root = heap.pop().unwrap(); // We have checked above that there is at least one value.
+ let mut bit_lengths = Vec::with_capacity(len);
+ fn aux<T>(bit_lengths: &mut Vec<(T, BitLen)>, depth: u8, node: NodeContent<T>) {
I thought the idea was to not make the 20 bits part of the spec?
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dominiccooney
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Sep 17, 2019
| @@ -113,11 +112,20 @@ where | |||
| { | |||
| /// Compute a `Keys` from a sequence of values. | |||
| /// | |||
| /// Optionally, `max_bit_len` may specify a largest acceptable bit length. | |||
| /// If `Keys` may not be computed without exceeding this bit length, | |||
| /// fail with `Err(problemantic_bit_length)`. | |||
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