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oxidation: Add implementation of bupsplit in Rust
This is an initial drop of "oxidation", or adding implementation of components in Rust. The bupsplit code is a good target - no dependencies, just computation. Translation into Rust had a few twists - - The C code relies a lot on overflowing unsigned ints, and also on the C promotion rules for e.g. `uint8_t -> int32_t` - There were some odd loops that I introduced bugs in while translating...in particular, the function always returns `len`, but I mistakenly translated to `len+1`, resulting in an OOB read on the C side, which was hard to debug. On the plus side, an off-by-one array indexing in the Rust code paniced nicely. In practice, we'll need a lot more build infrastructure to make this work, such as using `cargo vendor` when producing build artifacts for example. Also, Cargo is yet another thing we need to cache. Where do we go with this? Well, I think we should merge this, it's not a lot of code. We can just have it be an alternative CI target. Should we do a lot more right now? Probably not immediately, but I find the medium/long term prospects pretty exciting!
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| Original file line number | Diff line number | Diff line change |
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| [package] | ||
| name = "bupsplit" | ||
| version = "0.0.1" | ||
| authors = ["Colin Walters <[email protected]>"] | ||
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| [dependencies] | ||
| libc = "0.2" | ||
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| [lib] | ||
| name = "bupsplit_rs" | ||
| path = "src/bupsplit.rs" | ||
| crate-type = ["staticlib"] | ||
| panic = "abort" |
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| /* | ||
| * Copyright 2017 Colin Walters <[email protected]> | ||
| * Based on original bupsplit.c: | ||
| * Copyright 2011 Avery Pennarun. All rights reserved. | ||
| * | ||
| * (This license applies to bupsplit.c and bupsplit.h only.) | ||
| * | ||
| * Redistribution and use in source and binary forms, with or without | ||
| * modification, are permitted provided 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 AVERY PENNARUN ``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 <COPYRIGHT HOLDER> OR | ||
| * CONTRIBUTORS 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. | ||
| */ | ||
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| extern crate libc; | ||
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| use std::slice; | ||
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| // According to librsync/rollsum.h: | ||
| // "We should make this something other than zero to improve the | ||
| // checksum algorithm: tridge suggests a prime number." | ||
| // apenwarr: I unscientifically tried 0 and 7919, and they both ended up | ||
| // slightly worse than the librsync value of 31 for my arbitrary test data. | ||
| const ROLLSUM_CHAR_OFFSET: u32 = 31; | ||
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| // Previously in the header file | ||
| const BUP_BLOBBITS: u32= 13; | ||
| const BUP_BLOBSIZE: u32 = (1<<BUP_BLOBBITS); | ||
| const BUP_WINDOWBITS: u32 = 7; | ||
| const BUP_WINDOWSIZE: u32 = (1<<(BUP_WINDOWBITS-1)); | ||
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| struct Rollsum { | ||
| s1: u32, | ||
| s2: u32, | ||
| window: [u8; BUP_WINDOWSIZE as usize], | ||
| wofs: i32, | ||
| } | ||
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| impl Rollsum { | ||
| pub fn new() -> Rollsum { | ||
| Rollsum { s1: BUP_WINDOWSIZE * ROLLSUM_CHAR_OFFSET, | ||
| s2: BUP_WINDOWSIZE * (BUP_WINDOWSIZE-1) * ROLLSUM_CHAR_OFFSET, | ||
| window: [0; 64], | ||
| wofs: 0 | ||
| } | ||
| } | ||
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| // These formulas are based on rollsum.h in the librsync project. | ||
| pub fn add(&mut self, drop: u8, add: u8) -> () { | ||
| let drop_expanded = drop as u32; | ||
| let add_expanded = add as u32; | ||
| self.s1 = self.s1.wrapping_add(add_expanded.wrapping_sub(drop_expanded)); | ||
| self.s2 = self.s2.wrapping_add(self.s1.wrapping_sub(BUP_WINDOWSIZE * (drop_expanded + ROLLSUM_CHAR_OFFSET))); | ||
| } | ||
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| pub fn roll(&mut self, ch: u8) -> () { | ||
| let wofs = self.wofs as usize; | ||
| let dval = self.window[wofs]; | ||
| self.add(dval, ch); | ||
| self.window[wofs] = ch; | ||
| self.wofs = (self.wofs + 1) % (BUP_WINDOWSIZE as i32); | ||
| } | ||
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| pub fn digest(&self) -> u32 { | ||
| (self.s1 << 16) | (self.s2 & 0xFFFF) | ||
| } | ||
| } | ||
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| #[no_mangle] | ||
| pub extern fn bupsplit_sum(buf: *const u8, ofs: libc::size_t, len: libc::size_t) -> u32 { | ||
| let sbuf = unsafe { | ||
| assert!(!buf.is_null()); | ||
| slice::from_raw_parts(buf.offset(ofs as isize), (len - ofs) as usize) | ||
| }; | ||
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| let mut r = Rollsum::new(); | ||
| for x in sbuf { | ||
| r.roll(*x); | ||
| } | ||
| r.digest() | ||
| } | ||
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| #[no_mangle] | ||
| pub extern fn bupsplit_find_ofs(buf: *const u8, len: libc::size_t, | ||
| bits: *mut libc::c_int) -> libc::c_int | ||
| { | ||
| let sbuf = unsafe { | ||
| assert!(!buf.is_null()); | ||
| slice::from_raw_parts(buf, len as usize) | ||
| }; | ||
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| let mut r = Rollsum::new(); | ||
| for x in sbuf { | ||
| r.roll(*x); | ||
| if (r.s2 & (BUP_BLOBSIZE-1)) == ((u32::max_value()) & (BUP_BLOBSIZE-1)) { | ||
| if !bits.is_null() { | ||
| let mut sum = r.digest() >> BUP_BLOBBITS; | ||
| let mut rbits : libc::c_int = BUP_BLOBBITS as i32; | ||
| while sum & 1 != 0 { | ||
| sum = sum >> 1; | ||
| rbits = rbits + 1; | ||
| } | ||
| unsafe { | ||
| *bits = rbits; | ||
| } | ||
| } | ||
| return len as i32 | ||
| } | ||
| } | ||
| 0 | ||
| } |