wim/image-tiff
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Merge pull request #346 from RunDevelopment/invert-color-as-chunks

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More optimal code gen for `invert_colors`
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Aurelia Molzer authored and GitHub committed 2026-03-03 20:30:20 +00:00
2 parents 448a0e61d1 d872ff8751
commit 2b9476566b
1 file changed
+15 -32
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src/decoder/mod.rs
+15 -32
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@@ -717,46 +717,29 @@ fn invert_colors(
sample_format: SampleFormat,
) -> TiffResult<()> {
match (color_type, sample_format) {
// Where pixels do not cross a byte boundary
(ColorType::Gray(1 | 2 | 4 | 8), SampleFormat::Uint) => {
(ColorType::Gray(1 | 2 | 4 | 8 | 16 | 32 | 64), SampleFormat::Uint) => {
// It's guaranteed that pixels do not cross a byte boundary.
// To invert a single N-bit pixel, we can calculate:
// (2^N - 1) - x = (2^N - 1) + !x + 1 (because -x = !x + 1)
// = 2^n + !x
// = !x (because modular arithmetic)
//
// Further, since !x operates on bits independently, negating bytes
// also works for multi-byte pixels.
for x in buf {
// Equivalent to both of the following:
//
// *x = 0xff - *x
// *x = !*x
//
// since -x = !x+1
*x = !*x;
}
}
(ColorType::Gray(16), SampleFormat::Uint) => {
for x in buf.chunks_mut(2) {
let v = u16::from_ne_bytes(x.try_into().unwrap());
x.copy_from_slice(&(0xffff - v).to_ne_bytes());
}
}
(ColorType::Gray(32), SampleFormat::Uint) => {
for x in buf.chunks_mut(4) {
let v = u32::from_ne_bytes(x.try_into().unwrap());
x.copy_from_slice(&(0xffff_ffff - v).to_ne_bytes());
}
}
(ColorType::Gray(64), SampleFormat::Uint) => {
for x in buf.chunks_mut(8) {
let v = u64::from_ne_bytes(x.try_into().unwrap());
x.copy_from_slice(&(0xffff_ffff_ffff_ffff - v).to_ne_bytes());
}
}
(ColorType::Gray(32), SampleFormat::IEEEFP) => {
for x in buf.chunks_mut(4) {
let v = f32::from_ne_bytes(x.try_into().unwrap());
x.copy_from_slice(&(1.0 - v).to_ne_bytes());
for x in buf.as_chunks_mut::<4>().0 {
let v = f32::from_ne_bytes(*x);
*x = (1.0 - v).to_ne_bytes();
}
}
(ColorType::Gray(64), SampleFormat::IEEEFP) => {
for x in buf.chunks_mut(8) {
let v = f64::from_ne_bytes(x.try_into().unwrap());
x.copy_from_slice(&(1.0 - v).to_ne_bytes());
for x in buf.as_chunks_mut::<8>().0 {
let v = f64::from_ne_bytes(*x);
*x = (1.0 - v).to_ne_bytes();
}
}
_ => {