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Use NonZeroU64 to optimize encoded_len_varint #1192

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Use NonZeroU64 to optimize encoded_len_varint #1192

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7 changes: 5 additions & 2 deletions prost/src/encoding/varint.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
use core::cmp::min;
use core::num::NonZeroU64;

use ::bytes::{Buf, BufMut};

Expand All @@ -25,8 +26,10 @@ pub fn encode_varint(mut value: u64, buf: &mut impl BufMut) {
#[inline]
pub fn encoded_len_varint(value: u64) -> usize {
// Based on [VarintSize64][1].
// [1]: https://github.com/google/protobuf/blob/3.3.x/src/google/protobuf/io/coded_stream.h#L1301-L1309
((((value | 1).leading_zeros() ^ 63) * 9 + 73) / 64) as usize
// [1]: https://github.com/protocolbuffers/protobuf/blob/v28.3/src/google/protobuf/io/coded_stream.h#L1744-L1756
// Safety: value | 1 is non-zero.
let log2value = unsafe { NonZeroU64::new_unchecked(value | 1) }.ilog2();
((log2value * 9 + (64 + 9)) / 64) as usize
}

/// Decodes a LEB128-encoded variable length integer from the buffer.
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