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Reduce allocations while unfiltering by reusing buffers

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This commit is contained in:
Kamal Ahmad 2019-08-11 14:53:06 +05:00
parent 1a6284b177
commit e04153051c
2 changed files with 27 additions and 25 deletions
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42
src/filters.rs
View file

@ -62,30 +62,31 @@ pub fn filter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8], buf: &
}
}
pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> Vec<u8> {
let mut unfiltered = Vec::with_capacity(data.len());
pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8], buf: &mut Vec<u8>) {
assert_eq!(buf.len(), 0);
buf.reserve(data.len());
match filter {
0 => {
unfiltered.extend_from_slice(data);
buf.extend_from_slice(data);
}
1 => {
for (i, byte) in data.iter().enumerate() {
match i.checked_sub(bpp) {
Some(x) => {
let b = unfiltered[x];
unfiltered.push(byte.wrapping_add(b));
let b = buf[x];
buf.push(byte.wrapping_add(b));
}
None => {
unfiltered.push(*byte);
buf.push(*byte);
}
};
}
}
2 => {
if last_line.is_empty() {
unfiltered.extend_from_slice(data);
buf.extend_from_slice(data);
} else {
unfiltered.extend(
buf.extend(
data.iter()
.zip(last_line.iter())
.map(|(cur, last)| cur.wrapping_add(*last)),
@ -97,23 +98,23 @@ pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> V
if last_line.is_empty() {
match i.checked_sub(bpp) {
Some(x) => {
let b = unfiltered[x];
unfiltered.push(byte.wrapping_add(b >> 1));
let b = buf[x];
buf.push(byte.wrapping_add(b >> 1));
}
None => {
unfiltered.push(*byte);
buf.push(*byte);
}
};
} else {
match i.checked_sub(bpp) {
Some(x) => {
let b = unfiltered[x];
unfiltered.push(byte.wrapping_add(
let b = buf[x];
buf.push(byte.wrapping_add(
((u16::from(b) + u16::from(last_line[i])) >> 1) as u8,
));
}
None => {
unfiltered.push(byte.wrapping_add(last_line[i] >> 1));
buf.push(byte.wrapping_add(last_line[i] >> 1));
}
};
};
@ -124,25 +125,25 @@ pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> V
if last_line.is_empty() {
match i.checked_sub(bpp) {
Some(x) => {
let b = unfiltered[x];
unfiltered.push(byte.wrapping_add(b));
let b = buf[x];
buf.push(byte.wrapping_add(b));
}
None => {
unfiltered.push(*byte);
buf.push(*byte);
}
};
} else {
match i.checked_sub(bpp) {
Some(x) => {
let b = unfiltered[x];
unfiltered.push(byte.wrapping_add(paeth_predictor(
let b = buf[x];
buf.push(byte.wrapping_add(paeth_predictor(
b,
last_line[i],
last_line[x],
)));
}
None => {
unfiltered.push(byte.wrapping_add(last_line[i]));
buf.push(byte.wrapping_add(last_line[i]));
}
};
};
@ -150,7 +151,6 @@ pub fn unfilter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8]) -> V
}
_ => unreachable!(),
}
unfiltered
}
fn paeth_predictor(a: u8, b: u8, c: u8) -> u8 {

10
src/png/mod.rs
View file

@ -282,17 +282,19 @@ impl PngImage {
let bpp = ((self.ihdr.bit_depth.as_u8() * self.channels_per_pixel() + 7) / 8) as usize;
let mut last_line: Vec<u8> = Vec::new();
let mut last_pass = 1;
let mut unfiltered_buf = Vec::new();
for line in self.scan_lines() {
if let Some(pass) = line.pass {
if pass != last_pass {
last_line = Vec::new();
last_line.clear();
last_pass = pass;
}
}
let unfiltered_line = unfilter_line(line.filter, bpp, &line.data, &last_line);
unfilter_line(line.filter, bpp, &line.data, &last_line, &mut unfiltered_buf);
unfiltered.push(0);
unfiltered.extend_from_slice(&unfiltered_line);
last_line = unfiltered_line;
unfiltered.extend_from_slice(&unfiltered_buf);
std::mem::swap(&mut last_line, &mut unfiltered_buf);
unfiltered_buf.clear();
}
unfiltered
}