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https://github.com/storytold/craft-libs.git
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Dylan M. Taylor
603d43da85
PhotoCraft's YCbCr conversion (ReferenceBlackWhite, YCbCrCoefficients, libtiff-compatible green) and FilmCraft's decoding of uncompressed and PackBits subsampled chunky YCbCr images, with PackBits as its own module.
47 lines
1.7 KiB
Rust
47 lines
1.7 KiB
Rust
//! PackBits (TIFF 6.0 §9) decompression.
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/// Appends the bytes `src` decompresses to onto `out`, stopping once `out` holds `limit` bytes or
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/// at a run that the data ends inside. A header of −128 is a no-op.
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pub fn decode(src: &[u8], out: &mut Vec<u8>, limit: usize) {
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let mut p = 0;
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while out.len() < limit {
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let Some(&n) = src.get(p) else { return };
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let n = n as i8;
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p += 1;
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if n >= 0 {
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let len = n as usize + 1;
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let Some(lit) = p.checked_add(len).and_then(|end| src.get(p..end)) else { return };
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out.extend_from_slice(lit.get(..len.min(limit - out.len())).unwrap_or(lit));
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p += len;
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} else if n != -128 {
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let Some(&b) = src.get(p) else { return };
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let len = (1 - isize::from(n)) as usize;
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out.extend(std::iter::repeat_n(b, len.min(limit - out.len())));
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p += 1;
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn runs_literals_and_noops() {
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let mut out = Vec::new();
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// A literal of 2, a no-op, a run of 3, then a literal cut short by the end of the data.
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decode(&[1, 10, 11, 0x80, 0xFE, 7, 4, 1], &mut out, 100);
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assert_eq!(out, [10, 11, 7, 7, 7]);
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let mut capped = Vec::new();
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decode(&[0xFE, 7, 0xFE, 8], &mut capped, 4);
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assert_eq!(capped, [7, 7, 7, 8]);
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// The longest run, 128 bytes from two, appended to what is there.
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let mut out = vec![1];
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decode(&[0x81, 9], &mut out, 1000);
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assert_eq!((out.len(), out[1], out[128]), (129, 9, 9));
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let mut out = Vec::new();
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decode(&[0xFF], &mut out, 10);
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assert!(out.is_empty());
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}
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}
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