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improve encode_varint performance by bounding its loop #940

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Mar 15, 2024
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improve encode_varint performance by bounding its loop #940

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3 changes: 2 additions & 1 deletion src/encoding.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,8 @@ pub fn encode_varint<B>(mut value: u64, buf: &mut B)
where
B: BufMut,
{
loop {
// Varints are never more than 10 bytes
for _ in 0..10 {
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Can you explain the constant 10? Maybe a static assert, formula or documentation?

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is it not sufficiently covered by the comment already on this function? i can add it, just wondering

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Yeah, you are probably right. I saw that comment and started looking into why 10 bytes is correct. I took me a moment to understand.

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protobuf's varints are fairly thoroughly documented to be 10 bytes maximum, yes. i mean they could be 9 but they decided not to do that. i believe every minimal length protobuf varint that is 10 bytes always has 0x01 as its last byte value, which is rather a waste considering how many situations cause them to become maximum length this way. the burden of legacy i guess

if value < 0x80 {
buf.put_u8(value as u8);
break;
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