The LLVM bitcode requires all type references in
structs to be to earlier defined types.
We make sure types are ordered in the builder
itself in order to avoid having to iterate the
types multiple times and changing the values
of type indicies.
This commit works around #18967 by adding an `AccumulatingReader`, which
accumulates data read from the underlying packfile, and by keeping track
of the position in the packfile and hash/checksum information separately
rather than using reader composition. That is, the packfile position and
hashes/checksums are updated with the accumulated read history data only
after we can determine what data has actually been used by the
decompressor rather than merely being buffered.
The only addition to the standard library APIs to support this change is
the `unreadBytes` function in `std.compress.flate.Inflate`, which allows
the user to determine how many bytes have been read only for buffering
and not used as part of compressed data.
These changes can be reverted if #18967 is resolved with a decompressor
that reads precisely only the number of bytes needed for decompression.
Similar to the previous commit, errors coercing the panic message to
`[]const u8` now point at the operand to `@panic` rather than the actual
builtin call.
When coercing the operand of a `ret_node` etc instruction, the source
location for errors used to point to the entire `return` statement.
Instead, we now point to the operand, as would be expected if there was
an explicit `as_node` instruction (like there used to be).
Previously, the `src_node` field of `struct_decl`, `union_decl`,
`enum_decl`, and `opaque_decl` was optional, included in trailing data
only if a flag in `Small` was set. However, this was unnecessary logic:
AstGen always provided the source node. We can simplify a few bits of
logic by making this field non-optional, moving it into non-trailing
data.
There was one place where the field was actually omitted before: the
root struct of a file was at source node 0, so the node was
coincidentally elided. Therefore, this commit has a fixed cost of 4
bytes of ZIR per file.
In most cases where AstGen is coercing to a fixed type (such as `u29`,
`type`, `std.builtin.CallingConvention) we do not necessarily require an
explicit coercion instruction. Instead, Sema knows the type that is
required, and can perform the coercion after the fact. This means we can
use the `coerced_ty` result location kind, saving unnecessary coercion
instructions and therefore ZIR bytes.
This required a few enhancements to Sema to introduce missing coercions.
`sema.src` is a failed experiment. It introduces complexity, and makes
often unwarranted assumptions about the existence of instructions
providing source locations, requiring an unreasonable amount of caution
in AstGen for correctness. Eliminating it simplifies the whole frontend.
This required adding source locations to a few instructions, but the
cost in ZIR bytes should be counteracted by the other work on this
branch.
AstGen has logic to elide leading `dbg_stmt` instructions when multiple
are emitted consecutively; however, it only applied in some cases. A
simple reshuffle here makes this logic apply universally, saving some
bytes in ZIR.
This is a small optimization to generated ZIR. In any function where the
return type is not a trivial Ref, we know it is almost certainly not
`void` (unless the user aliased it or did something else weird to fool
AstGen), and thus the return type is very likely to be required for
return value RLS at some point. Thus, we can just emit one `ret_type` at
the start of the function and use it throughout.
This sees a very small improvement in overall ZIR bytes.
Zig deflate compression/decompression implementation. It supports compression and decompression of gzip, zlib and raw deflate format.
Fixes#18062.
This PR replaces current compress/gzip and compress/zlib packages. Deflate package is renamed to flate. Flate is common name for deflate/inflate where deflate is compression and inflate decompression.
There are breaking change. Methods signatures are changed because of removal of the allocator, and I also unified API for all three namespaces (flate, gzip, zlib).
Currently I put old packages under v1 namespace they are still available as compress/v1/gzip, compress/v1/zlib, compress/v1/deflate. Idea is to give users of the current API little time to postpone analyzing what they had to change. Although that rises question when it is safe to remove that v1 namespace.
Here is current API in the compress package:
```Zig
// deflate
fn compressor(allocator, writer, options) !Compressor(@TypeOf(writer))
fn Compressor(comptime WriterType) type
fn decompressor(allocator, reader, null) !Decompressor(@TypeOf(reader))
fn Decompressor(comptime ReaderType: type) type
// gzip
fn compress(allocator, writer, options) !Compress(@TypeOf(writer))
fn Compress(comptime WriterType: type) type
fn decompress(allocator, reader) !Decompress(@TypeOf(reader))
fn Decompress(comptime ReaderType: type) type
// zlib
fn compressStream(allocator, writer, options) !CompressStream(@TypeOf(writer))
fn CompressStream(comptime WriterType: type) type
fn decompressStream(allocator, reader) !DecompressStream(@TypeOf(reader))
fn DecompressStream(comptime ReaderType: type) type
// xz
fn decompress(allocator: Allocator, reader: anytype) !Decompress(@TypeOf(reader))
fn Decompress(comptime ReaderType: type) type
// lzma
fn decompress(allocator, reader) !Decompress(@TypeOf(reader))
fn Decompress(comptime ReaderType: type) type
// lzma2
fn decompress(allocator, reader, writer !void
// zstandard:
fn DecompressStream(ReaderType, options) type
fn decompressStream(allocator, reader) DecompressStream(@TypeOf(reader), .{})
struct decompress
```
The proposed naming convention:
- Compressor/Decompressor for functions which return type, like Reader/Writer/GeneralPurposeAllocator
- compressor/compressor for functions which are initializers for that type, like reader/writer/allocator
- compress/decompress for one shot operations, accepts reader/writer pair, like read/write/alloc
```Zig
/// Compress from reader and write compressed data to the writer.
fn compress(reader: anytype, writer: anytype, options: Options) !void
/// Create Compressor which outputs the writer.
fn compressor(writer: anytype, options: Options) !Compressor(@TypeOf(writer))
/// Compressor type
fn Compressor(comptime WriterType: type) type
/// Decompress from reader and write plain data to the writer.
fn decompress(reader: anytype, writer: anytype) !void
/// Create Decompressor which reads from reader.
fn decompressor(reader: anytype) Decompressor(@TypeOf(reader)
/// Decompressor type
fn Decompressor(comptime ReaderType: type) type
```
Comparing this implementation with the one we currently have in Zig's standard library (std).
Std is roughly 1.2-1.4 times slower in decompression, and 1.1-1.2 times slower in compression. Compressed sizes are pretty much same in both cases.
More resutls in [this](https://github.com/ianic/flate) repo.
This library uses static allocations for all structures, doesn't require allocator. That makes sense especially for deflate where all structures, internal buffers are allocated to the full size. Little less for inflate where we std version uses less memory by not preallocating to theoretical max size array which are usually not fully used.
For deflate this library allocates 395K while std 779K.
For inflate this library allocates 74.5K while std around 36K.
Inflate difference is because we here use 64K history instead of 32K in std.
If merged existing usage of compress gzip/zlib/deflate need some changes. Here is example with necessary changes in comments:
```Zig
const std = @import("std");
// To get this file:
// wget -nc -O war_and_peace.txt https://www.gutenberg.org/ebooks/2600.txt.utf-8
const data = @embedFile("war_and_peace.txt");
pub fn main() !void {
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
defer std.debug.assert(gpa.deinit() == .ok);
const allocator = gpa.allocator();
try oldDeflate(allocator);
try new(std.compress.flate, allocator);
try oldZlib(allocator);
try new(std.compress.zlib, allocator);
try oldGzip(allocator);
try new(std.compress.gzip, allocator);
}
pub fn new(comptime pkg: type, allocator: std.mem.Allocator) !void {
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Compressor
var cmp = try pkg.compressor(buf.writer(), .{});
_ = try cmp.write(data);
try cmp.finish();
var fbs = std.io.fixedBufferStream(buf.items);
// Decompressor
var dcp = pkg.decompressor(fbs.reader());
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
pub fn oldDeflate(allocator: std.mem.Allocator) !void {
const deflate = std.compress.v1.deflate;
// Compressor
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Remove allocator
// Rename deflate -> flate
var cmp = try deflate.compressor(allocator, buf.writer(), .{});
_ = try cmp.write(data);
try cmp.close(); // Rename to finish
cmp.deinit(); // Remove
// Decompressor
var fbs = std.io.fixedBufferStream(buf.items);
// Remove allocator and last param
// Rename deflate -> flate
// Remove try
var dcp = try deflate.decompressor(allocator, fbs.reader(), null);
defer dcp.deinit(); // Remove
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
pub fn oldZlib(allocator: std.mem.Allocator) !void {
const zlib = std.compress.v1.zlib;
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Compressor
// Rename compressStream => compressor
// Remove allocator
var cmp = try zlib.compressStream(allocator, buf.writer(), .{});
_ = try cmp.write(data);
try cmp.finish();
cmp.deinit(); // Remove
var fbs = std.io.fixedBufferStream(buf.items);
// Decompressor
// decompressStream => decompressor
// Remove allocator
// Remove try
var dcp = try zlib.decompressStream(allocator, fbs.reader());
defer dcp.deinit(); // Remove
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
pub fn oldGzip(allocator: std.mem.Allocator) !void {
const gzip = std.compress.v1.gzip;
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Compressor
// Rename compress => compressor
// Remove allocator
var cmp = try gzip.compress(allocator, buf.writer(), .{});
_ = try cmp.write(data);
try cmp.close(); // Rename to finisho
cmp.deinit(); // Remove
var fbs = std.io.fixedBufferStream(buf.items);
// Decompressor
// Rename decompress => decompressor
// Remove allocator
// Remove try
var dcp = try gzip.decompress(allocator, fbs.reader());
defer dcp.deinit(); // Remove
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
```
