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Use ZPAQ algorithm as specified by zpaq206.pdf #7

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Use ZPAQ algorithm as specified by zpaq206.pdf #7

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20 changes: 10 additions & 10 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -473,7 +473,8 @@ impl<I: ChunkerImpl> ChunkerImpl for SizeLimited<I> {
}
}

const HM: Wrapping<u32> = Wrapping(123_456_791);
const HM1: Wrapping<u32> = Wrapping(314_159_265);
const HM2: Wrapping<u32> = Wrapping(271_828_182);

pub struct ZPAQ {
nbits: usize,
Expand All @@ -488,15 +489,15 @@ impl ZPAQ {
nbits: 32 - nbits,
c1: 0,
o1: [0; 256],
h: HM,
h: Wrapping(0),
}
}

pub fn update(&mut self, byte: u8) -> bool {
if byte == self.o1[self.c1 as usize] {
self.h = self.h * HM + Wrapping(byte as u32 + 1);
self.h = HM1 * (self.h + Wrapping(byte as u32 + 1));
} else {
self.h = self.h * HM * Wrapping(2) + Wrapping(byte as u32 + 1);
self.h = HM2 * (self.h + Wrapping(byte as u32 + 1));
}
self.o1[self.c1 as usize] = byte;
self.c1 = byte;
Expand All @@ -521,7 +522,7 @@ impl ChunkerImpl for ZPAQ {
fn reset(&mut self) {
self.c1 = 0u8;
self.o1.clone_from_slice(&[0u8; 256]);
self.h = HM;
self.h = Wrapping(0);
}
}

Expand All @@ -542,7 +543,7 @@ mod tests {
let rollinghash = ZPAQ::new(3); // 8-bit chunk average
let chunker = Chunker::new(rollinghash);
let data = b"defghijklmnopqrstuvwxyz1234567890";
let expected = b"def|ghijk|lmno|pq|rstuvw|xyz123|4567890|";
let expected = b"de|fghijklmnopqr|stuvwxyz12345|67890|";
(chunker, data, io::Cursor::new(data), expected)
}

Expand Down Expand Up @@ -632,8 +633,7 @@ mod tests {
assert_eq!(
result,
vec![
(0, 3), (3, 5), (8, 4), (12, 2),
(14, 6), (20, 6), (26, 7),
(0, 2), (2, 13), (15, 13), (28, 5),
]
);
}
Expand All @@ -654,8 +654,8 @@ mod tests {
assert_eq!(
result,
vec![
(0, 3), (3, 5), (8, 4), (12, 2),
(14, 5), (19, 5), (24, 3), (27, 5), (32, 1),
(0, 2), (2, 5), (7, 5), (12, 2),
(14, 5), (19, 5), (24, 5), (29, 4),
]
);
}
Expand Down