aehobak 0.0.6

Transcoder for bsdiff binary patches.
Documentation 
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/*-
 * Copyright 2024 David Michael Barr
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted providing that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

use crate::control::Aehobak as AehobakControl;
use crate::control::Bsdiff as BsdiffControl;
use std::io;
use streamvbyte64::{Coder, Coder0124};

/// Directly apply a compact representation of bsdiff output.
#[allow(clippy::ptr_arg)]
pub fn patch(old: &[u8], mut patch: &[u8], new: &mut Vec<u8>) -> io::Result<()> {
    let coder = Coder0124::new();

    let prefix_len = 1 + coder.data_len(&patch[..1]);
    let (controls_len, deltas_len, control_data_len, literals_len) = {
        let mut v = [0u32; 4];
        coder.decode(&patch[..1], &patch[1..], &mut v);
        (v[0] as usize, v[1] as usize, v[2] as usize, v[3] as usize)
    };
    patch = &patch[prefix_len..];

    let control_tags_len = (controls_len * 3 + 3) / 4;
    let delta_tags_len = (deltas_len + 3) / 4;

    let control_tags = &patch[..control_tags_len];
    patch = &patch[control_tags_len..];
    let delta_tags = &patch[..delta_tags_len];
    patch = &patch[delta_tags_len..];
    let control_data = &patch[..patch.len().min(16 + control_data_len)];
    patch = &patch[control_data_len..];
    let mut literals = &patch[..literals_len];
    patch = &patch[literals_len..];
    let delta_data_len = coder.data_len(delta_tags);
    let delta_data = &patch[..patch.len().min(16 + delta_data_len)];
    patch = &patch[delta_data_len..];
    let mut delta_diffs = &patch[..deltas_len];

    let mut u32_buf = vec![0; 4 * (control_tags_len + delta_tags_len)];
    let (controls, delta_skips) = u32_buf.split_at_mut(4 * control_tags_len);

    let _ = coder.decode(control_tags, control_data, controls);
    let controls = &controls[..controls_len * 3];
    let _ = coder.decode(delta_tags, delta_data, delta_skips);
    let mut delta_skips = &delta_skips[..deltas_len];

    let mut old_cursor = 0i64;
    let mut delta_cursor = 0;
    let mut stream_cursor = 0;

    for buffer in controls.chunks_exact(3) {
        let control: BsdiffControl = (&AehobakControl::try_from(buffer).unwrap()).into();
        let (add, copy) = (control.add as usize, control.copy as usize);
        let new_cursor = new.len();
        new.extend(&old[old_cursor as usize..][..add]);
        while !delta_skips.is_empty() && !delta_diffs.is_empty() {
            let new_delta_cursor = delta_cursor + delta_skips[0] as usize;
            if new_delta_cursor >= stream_cursor + add {
                break;
            }
            let new_byte = &mut new[new_delta_cursor - stream_cursor + new_cursor];
            *new_byte = new_byte.wrapping_add(delta_diffs[0]);
            delta_cursor = new_delta_cursor + 1;
            delta_skips = &delta_skips[1..];
            delta_diffs = &delta_diffs[1..];
        }
        new.extend(&literals[..copy]);
        literals = &literals[copy..];
        stream_cursor += add;
        old_cursor += add as i64;
        old_cursor += control.seek;
    }
    Ok(())
}