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Merged
nuskey8 merged 2 commits into from
Jul 25, 2026
Merged

optimize: SliceReader::skip_value() #55

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a56df17
optimize: `SliceReader::skip_value()`
nuskey8 Jul 25, 2026
dc23dbc
chore: add bench
nuskey8 Jul 25, 2026
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40 changes: 40 additions & 0 deletions zerompk/benches/skip_value.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,40 @@
#![feature(test)]

extern crate test;

use zerompk::{Read, SliceReader};

const VALUES: usize = 10_000;

#[bench]
fn skip_large_scalar_array(b: &mut test::Bencher) {
let mut data = Vec::with_capacity(VALUES + 5);
data.push(0xdd); // array32
data.extend_from_slice(&(VALUES as u32).to_be_bytes());
data.resize(data.len() + VALUES, 1); // positive fixints

b.bytes = data.len() as u64;
b.iter(|| {
let mut reader = SliceReader::new(test::black_box(&data));
reader.skip_value().unwrap();
test::black_box(reader);
});
}

#[bench]
fn skip_large_u32_array(b: &mut test::Bencher) {
let mut data = Vec::with_capacity(VALUES * 5 + 5);
data.push(0xdd); // array32
data.extend_from_slice(&(VALUES as u32).to_be_bytes());
for value in 0..VALUES as u32 {
data.push(0xce); // uint32
data.extend_from_slice(&value.to_be_bytes());
}

b.bytes = data.len() as u64;
b.iter(|| {
let mut reader = SliceReader::new(test::black_box(&data));
reader.skip_value().unwrap();
test::black_box(reader);
});
}
91 changes: 51 additions & 40 deletions zerompk/src/read.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -266,6 +266,25 @@ impl<'de> SliceReader<'de> {
buffer_too_small()
}
}

#[inline(always)]
fn skip_array_values(&mut self, len: usize) -> Result<()> {
self.increment_depth()?;
let result = (0..len).try_for_each(|_| self.skip_value());
self.decrement_depth();
result
}

#[inline(always)]
fn skip_map_entries(&mut self, len: usize) -> Result<()> {
self.increment_depth()?;
let result = (0..len).try_for_each(|_| {
self.skip_value()?;
self.skip_value()
});
self.decrement_depth();
result
}
}

impl<'de> Read<'de> for SliceReader<'de> {
Expand Down Expand Up @@ -365,7 +384,6 @@ impl<'de> Read<'de> for SliceReader<'de> {
}

fn skip_value(&mut self) -> Result<()> {
self.increment_depth()?;
let byte = self.peek_byte()?;
match byte {
POS_FIXINT_START..=POS_FIXINT_END | NEG_FIXINT_START..=NEG_FIXINT_END => {
Expand All @@ -375,25 +393,20 @@ impl<'de> Read<'de> for SliceReader<'de> {
self.pos += 1;
}
UINT8_MARKER | INT8_MARKER => {
self.pos += 1;
self.take_slice(1)?;
self.take_slice(2)?;
}
UINT16_MARKER | INT16_MARKER => {
self.pos += 1;
self.take_slice(2)?;
self.take_slice(3)?;
}
UINT32_MARKER | INT32_MARKER | FLOAT32_MARKER => {
self.pos += 1;
self.take_slice(4)?;
self.take_slice(5)?;
}
UINT64_MARKER | INT64_MARKER | FLOAT64_MARKER => {
self.pos += 1;
self.take_slice(8)?;
self.take_slice(9)?;
}
FIXSTR_START..=FIXSTR_END => {
let len = (byte - FIXSTR_START) as usize;
self.pos += 1;
self.take_slice(len)?;
self.take_slice(len + 1)?;
}
STR8_MARKER | BIN8_MARKER => {
self.pos += 1;
Expand All @@ -415,68 +428,51 @@ impl<'de> Read<'de> for SliceReader<'de> {
FIXARRAY_START..=FIXARRAY_END => {
let len = (byte - FIXARRAY_START) as usize;
self.pos += 1;
for _ in 0..len {
self.skip_value()?;
}
self.skip_array_values(len)?;
}
ARRAY16_MARKER => {
self.pos += 1;
let bytes = self.take_array::<2>()?;
let len = u16::from_be_bytes(*bytes) as usize;
for _ in 0..len {
self.skip_value()?;
}
self.skip_array_values(len)?;
}
ARRAY32_MARKER => {
self.pos += 1;
let bytes = self.take_array::<4>()?;
let len = u32::from_be_bytes(*bytes) as usize;
for _ in 0..len {
self.skip_value()?;
}
self.skip_array_values(len)?;
}
FIXMAP_START..=FIXMAP_END => {
let len = (byte - FIXMAP_START) as usize;
self.pos += 1;
for _ in 0..(len * 2) {
self.skip_value()?;
}
self.skip_map_entries(len)?;
}
MAP16_MARKER => {
self.pos += 1;
let bytes = self.take_array::<2>()?;
let len = u16::from_be_bytes(*bytes) as usize;
for _ in 0..(len * 2) {
self.skip_value()?;
}
self.skip_map_entries(len)?;
}
MAP32_MARKER => {
self.pos += 1;
let bytes = self.take_array::<4>()?;
let len = u32::from_be_bytes(*bytes) as usize;
for _ in 0..(len * 2) {
self.skip_value()?;
}
self.skip_map_entries(len)?;
}
FIXEXT1_MARKER => {
self.pos += 1;
self.take_slice(2)?;
self.take_slice(3)?;
}
FIXEXT2_MARKER => {
self.pos += 1;
self.take_slice(3)?;
self.take_slice(4)?;
}
FIXEXT4_MARKER => {
self.pos += 1;
self.take_slice(5)?;
self.take_slice(6)?;
}
FIXEXT8_MARKER => {
self.pos += 1;
self.take_slice(9)?;
self.take_slice(10)?;
}
FIXEXT16_MARKER => {
self.pos += 1;
self.take_slice(17)?;
self.take_slice(18)?;
}
EXT8_MARKER => {
self.pos += 1;
Expand All @@ -497,7 +493,6 @@ impl<'de> Read<'de> for SliceReader<'de> {
}
_ => return Err(Error::InvalidMarker(byte)),
}
self.decrement_depth();
Ok(())
}
}
Expand Down Expand Up @@ -816,6 +811,22 @@ mod tests {
assert_eq!(reader.depth, 0);
}

#[test]
fn slice_reader_skip_value_restores_depth_after_nested_error() {
let data = [
0x91, // fixarray with one value
0x91, // nested fixarray with one value
0xc1, // reserved marker
];
let mut reader = SliceReader::new(&data);

assert!(matches!(
reader.skip_value(),
Err(Error::InvalidMarker(0xc1))
));
assert_eq!(reader.depth, 0);
}

#[cfg(feature = "std")]
#[test]
fn io_reader_decrement_depth_at_zero_does_not_underflow() {
Expand Down