comparison rust/hg-core/src/dirstate_tree/on_disk.rs @ 47476:f23eafb036af

dirstate-v2: Use 32-bit integers instead of 64-bit for offsets

This saves 12 bytes per node. (Nodes representing files or directories.)

These are offsets to other parts of the file. This would only be a limitation
for a `.hg/dirstate` file larger than 4 GiB, which would only happen for a
repository with dozens of millions of files and directories.

Differential Revision: https://phab.mercurial-scm.org/D10920

47475:94e38822d395

use crate::utils::hg_path::HgPath;
use crate::DirstateEntry;
use crate::DirstateError;
use crate::DirstateParents;
use crate::EntryState;
use bytes_cast::unaligned::{I32Be, I64Be, U32Be, U64Be};
use bytes_cast::BytesCast;
use std::borrow::Cow;
use std::convert::TryFrom;
use std::time::{Duration, SystemTime, UNIX_EPOCH};

    nanoseconds: U32Be,
}

/// Counted in bytes from the start of the file
///
/// NOTE: If we decide to never support `.hg/dirstate` files larger than 4 GiB
/// we could save space by using `U32Be` instead.
type Offset = U64Be;

/// Counted in number of items
///
/// NOTE: not supporting directories with more than 4 billion direct children,
/// or filenames more than 4 GiB.

/// Either nothing if `start == 0`, or a `HgPath` of `len` bytes
type OptPathSlice = Slice;

/// Make sure that size-affecting changes are made knowingly
fn _static_assert_size_of() {
    let _ = std::mem::transmute::<Header, [u8; 92]>;
    let _ = std::mem::transmute::<Node, [u8; 57]>;
}

/// Unexpected file format found in `.hg/dirstate` with the "v2" format.
///
/// This should only happen if Mercurial is buggy or a repository is corrupted.

fn write_slice<T>(slice: &[T], out: &mut Vec<u8>) -> Slice
where
    T: BytesCast,
{
    let start = u64::try_from(out.len())
        // Could only panic on a 128-bit CPU with a dirstate over 16 EiB
        .expect("dirstate-v2 offset overflow")
        .into();
    let len = u32::try_from(slice.len())
        // Could only panic for paths over 4 GiB or nodes with over 4 billions
        // child nodes

47476:f23eafb036af

use crate::utils::hg_path::HgPath;
use crate::DirstateEntry;
use crate::DirstateError;
use crate::DirstateParents;
use crate::EntryState;
use bytes_cast::unaligned::{I32Be, I64Be, U32Be};
use bytes_cast::BytesCast;
use std::borrow::Cow;
use std::convert::TryFrom;
use std::time::{Duration, SystemTime, UNIX_EPOCH};

    nanoseconds: U32Be,
}

/// Counted in bytes from the start of the file
///
/// NOTE: not supporting `.hg/dirstate` files larger than 4 GiB.
type Offset = U32Be;

/// Counted in number of items
///
/// NOTE: not supporting directories with more than 4 billion direct children,
/// or filenames more than 4 GiB.

/// Either nothing if `start == 0`, or a `HgPath` of `len` bytes
type OptPathSlice = Slice;

/// Make sure that size-affecting changes are made knowingly
fn _static_assert_size_of() {
    let _ = std::mem::transmute::<Header, [u8; 88]>;
    let _ = std::mem::transmute::<Node, [u8; 45]>;
}

/// Unexpected file format found in `.hg/dirstate` with the "v2" format.
///
/// This should only happen if Mercurial is buggy or a repository is corrupted.

fn write_slice<T>(slice: &[T], out: &mut Vec<u8>) -> Slice
where
    T: BytesCast,
{
    let start = u32::try_from(out.len())
        // Could only panic for a dirstate file larger than 4 GiB
        .expect("dirstate-v2 offset overflow")
        .into();
    let len = u32::try_from(slice.len())
        // Could only panic for paths over 4 GiB or nodes with over 4 billions
        // child nodes