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std.compress.flate.Decompress: use 64 buffered bits

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will have to find out why usize doesn't work for 32 bit targets some
other time
This commit is contained in:
Andrew Kelley 2025-08-01 09:04:27 -07:00
parent eb17d4562a
commit a6f7927764
1 changed files with 21 additions and 18 deletions
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39
lib/std/compress/flate/Decompress.zig
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@ -10,8 +10,8 @@ const Decompress = @This();
const Token = @import("Token.zig");
input: *Reader,
next_bits: usize,
remaining_bits: std.math.Log2Int(usize),
next_bits: Bits,
remaining_bits: std.math.Log2Int(Bits),
reader: Reader,
@ -25,6 +25,9 @@ state: State,
err: ?Error,
/// TODO: change this to usize
const Bits = u64;
const BlockType = enum(u2) {
stored = 0,
fixed = 1,
@ -498,14 +501,14 @@ fn takeBits(d: *Decompress, comptime U: type) !U {
return u;
}
const in = d.input;
const next_int = in.takeInt(usize, .little) catch |err| switch (err) {
const next_int = in.takeInt(Bits, .little) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => return takeBitsEnding(d, U),
};
const needed_bits = @bitSizeOf(U) - remaining_bits;
const u: U = @intCast(((next_int & ((@as(usize, 1) << needed_bits) - 1)) << remaining_bits) | next_bits);
const u: U = @intCast(((next_int & ((@as(Bits, 1) << needed_bits) - 1)) << remaining_bits) | next_bits);
d.next_bits = next_int >> needed_bits;
d.remaining_bits = @intCast(@bitSizeOf(usize) - @as(usize, needed_bits));
d.remaining_bits = @intCast(@bitSizeOf(Bits) - @as(usize, needed_bits));
return u;
}
@ -514,14 +517,14 @@ fn takeBitsEnding(d: *Decompress, comptime U: type) !U {
const next_bits = d.next_bits;
const in = d.input;
const n = in.bufferedLen();
assert(n < @sizeOf(usize));
assert(n < @sizeOf(Bits));
const needed_bits = @bitSizeOf(U) - remaining_bits;
if (n * 8 < needed_bits) return error.EndOfStream;
const next_int = in.takeVarInt(usize, .little, n) catch |err| switch (err) {
const next_int = in.takeVarInt(Bits, .little, n) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => unreachable,
};
const u: U = @intCast(((next_int & ((@as(usize, 1) << needed_bits) - 1)) << remaining_bits) | next_bits);
const u: U = @intCast(((next_int & ((@as(Bits, 1) << needed_bits) - 1)) << remaining_bits) | next_bits);
d.next_bits = next_int >> needed_bits;
d.remaining_bits = @intCast(n * 8 - @as(usize, needed_bits));
return u;
@ -532,37 +535,37 @@ fn peekBits(d: *Decompress, comptime U: type) !U {
const next_bits = d.next_bits;
if (remaining_bits >= @bitSizeOf(U)) return @truncate(next_bits);
const in = d.input;
const next_int = in.peekInt(usize, .little) catch |err| switch (err) {
const next_int = in.peekInt(Bits, .little) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => return peekBitsEnding(d, U),
};
const needed_bits = @bitSizeOf(U) - remaining_bits;
return @intCast(((next_int & ((@as(usize, 1) << needed_bits) - 1)) << remaining_bits) | next_bits);
return @intCast(((next_int & ((@as(Bits, 1) << needed_bits) - 1)) << remaining_bits) | next_bits);
}
fn peekBitsEnding(d: *Decompress, comptime U: type) !U {
const remaining_bits = d.remaining_bits;
const next_bits = d.next_bits;
const in = d.input;
var u: usize = 0;
var u: Bits = 0;
var remaining_needed_bits = @bitSizeOf(U) - remaining_bits;
var i: usize = 0;
while (remaining_needed_bits >= 8) {
const byte = try specialPeek(in, next_bits, i);
u |= @as(usize, byte) << @intCast(i * 8);
u |= @as(Bits, byte) << @intCast(i * 8);
remaining_needed_bits -= 8;
i += 1;
}
if (remaining_needed_bits != 0) {
const byte = try specialPeek(in, next_bits, i);
u |= @as(usize, byte) << @intCast((i * 8) + remaining_needed_bits);
u |= @as(Bits, byte) << @intCast((i * 8) + remaining_needed_bits);
}
return @truncate((u << remaining_bits) | next_bits);
}
/// If there is any unconsumed data, handles EndOfStream by pretending there
/// are zeroes afterwards.
fn specialPeek(in: *Reader, next_bits: usize, i: usize) Reader.Error!u8 {
fn specialPeek(in: *Reader, next_bits: Bits, i: usize) Reader.Error!u8 {
const peeked = in.peek(i + 1) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => if (next_bits == 0 and i == 0) return error.EndOfStream else return 0,
@ -578,13 +581,13 @@ fn tossBits(d: *Decompress, n: u4) !void {
d.remaining_bits = remaining_bits - n;
} else {
const in = d.input;
const next_int = in.takeInt(usize, .little) catch |err| switch (err) {
const next_int = in.takeInt(Bits, .little) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => return tossBitsEnding(d, n),
};
const needed_bits = n - remaining_bits;
d.next_bits = next_int >> needed_bits;
d.remaining_bits = @intCast(@bitSizeOf(usize) - @as(usize, needed_bits));
d.remaining_bits = @intCast(@bitSizeOf(Bits) - @as(usize, needed_bits));
}
}
@ -593,9 +596,9 @@ fn tossBitsEnding(d: *Decompress, n: u4) !void {
const in = d.input;
const buffered_n = in.bufferedLen();
if (buffered_n == 0) return error.EndOfStream;
assert(buffered_n < @sizeOf(usize));
assert(buffered_n < @sizeOf(Bits));
const needed_bits = n - remaining_bits;
const next_int = in.takeVarInt(usize, .little, buffered_n) catch |err| switch (err) {
const next_int = in.takeVarInt(Bits, .little, buffered_n) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => unreachable,
};