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/// Given the decompressed pack delta `d`, decode a size in bytes (either the base object size or the result object size)
/// Equivalent to [this canonical git function](https://github.com/git/git/blob/311531c9de557d25ac087c1637818bd2aad6eb3a/delta.h#L89)
pub fn decode_header_size(d: &[u8]) -> (u64, usize) {
let mut i = 0;
let mut size = 0u64;
let mut consumed = 0;
for cmd in d.iter() {
consumed += 1;
size |= (*cmd as u64 & 0x7f) << i;
i += 7;
if *cmd & 0x80 == 0 {
break;
}
}
(size, consumed)
}
pub fn apply(base: &[u8], mut target: &mut [u8], data: &[u8]) {
let mut i = 0;
while let Some(cmd) = data.get(i) {
i += 1;
match cmd {
cmd if cmd & 0b1000_0000 != 0 => {
let (mut ofs, mut size): (u32, u32) = (0, 0);
if cmd & 0b0000_0001 != 0 {
ofs = data[i] as u32;
i += 1;
}
if cmd & 0b0000_0010 != 0 {
ofs |= (data[i] as u32) << 8;
i += 1;
}
if cmd & 0b0000_0100 != 0 {
ofs |= (data[i] as u32) << 16;
i += 1;
}
if cmd & 0b0000_1000 != 0 {
ofs |= (data[i] as u32) << 24;
i += 1;
}
if cmd & 0b0001_0000 != 0 {
size = data[i] as u32;
i += 1;
}
if cmd & 0b0010_0000 != 0 {
size |= (data[i] as u32) << 8;
i += 1;
}
if cmd & 0b0100_0000 != 0 {
size |= (data[i] as u32) << 16;
i += 1;
}
if size == 0 {
size = 0x10000; // 65536
}
let ofs = ofs as usize;
std::io::Write::write(&mut target, &base[ofs..ofs + size as usize])
.expect("delta copy from base: byte slices must match");
}
0 => panic!("encountered unsupported command code: 0"),
size => {
std::io::Write::write(&mut target, &data[i..i + *size as usize])
.expect("delta copy data: slice sizes to match up");
i += *size as usize;
}
}
}
assert_eq!(i, data.len());
assert_eq!(target.len(), 0);
}
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