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simplify tossBitsEnding

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This commit is contained in:
Andrew Kelley 2025-07-28 21:05:33 -07:00
parent 5bc63794cc
commit 2569f4ff85
1 changed files with 30 additions and 18 deletions
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48
lib/std/compress/flate/Decompress.zig
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@ -219,7 +219,7 @@ fn readInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader.S
const block_type: BlockType = @enumFromInt(try d.takeBits(u2));
switch (block_type) {
.stored => {
d.alignBitsToByte(); // skip padding until byte boundary
d.alignBitsDiscarding();
// everything after this is byte aligned in stored block
const len = try in.takeInt(u16, .little);
const nlen = try in.takeInt(u16, .little);
@ -333,20 +333,23 @@ fn readInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader.S
return @intFromEnum(limit) - remaining;
},
.protocol_footer => {
d.alignBitsToByte();
switch (d.container_metadata) {
.gzip => |*gzip| {
d.alignBitsDiscarding();
gzip.* = .{
.crc = try in.takeInt(u32, .little),
.count = try in.takeInt(u32, .little),
};
},
.zlib => |*zlib| {
d.alignBitsDiscarding();
zlib.* = .{
.adler = try in.takeInt(u32, .little),
};
},
.raw => {},
.raw => {
d.alignBitsPreserving();
},
}
d.state = .end;
return 0;
@ -475,22 +478,16 @@ fn tossBits(d: *Decompress, n: u6) !void {
fn tossBitsEnding(d: *Decompress, n: u6) !void {
const remaining_bits = d.remaining_bits;
const in = d.input;
var remaining_needed_bits = n - remaining_bits;
while (remaining_needed_bits >= 8) {
try in.discardAll(1);
remaining_needed_bits -= 8;
}
if (remaining_needed_bits == 0) {
d.next_bits = 0;
d.remaining_bits = 0;
return;
}
const byte = in.takeByte() catch |err| switch (err) {
const buffered_n = in.bufferedLen();
if (buffered_n == 0) return error.EndOfStream;
assert(buffered_n < @sizeOf(usize));
const needed_bits = n - remaining_bits;
const next_int = in.takeVarInt(usize, .little, buffered_n) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => if (remaining_bits == 0) return error.EndOfStream else 0,
error.EndOfStream => unreachable,
};
d.next_bits = @as(usize, byte) >> remaining_needed_bits;
d.remaining_bits = @intCast(8 - remaining_needed_bits);
d.next_bits = next_int >> needed_bits;
d.remaining_bits = @intCast(@as(usize, n) * 8 -| @as(usize, needed_bits));
}
fn takeBitsRuntime(d: *Decompress, n: u4) !u16 {
@ -501,7 +498,7 @@ fn takeBitsRuntime(d: *Decompress, n: u4) !u16 {
return u;
}
fn alignBitsToByte(d: *Decompress) void {
fn alignBitsDiscarding(d: *Decompress) void {
const remaining_bits = d.remaining_bits;
const next_bits = d.next_bits;
if (remaining_bits == 0) return;
@ -518,6 +515,21 @@ fn alignBitsToByte(d: *Decompress) void {
d.next_bits = 0;
}
fn alignBitsPreserving(d: *Decompress) void {
const remaining_bits: usize = d.remaining_bits;
if (remaining_bits == 0) return;
const n_bytes = (remaining_bits + 7) / 8;
const in = d.input;
in.seek -= n_bytes;
var put_back_bits = d.next_bits;
for (in.buffer[in.seek..][0..n_bytes]) |*b| {
b.* = @truncate(put_back_bits);
put_back_bits >>= 8;
}
d.remaining_bits = 0;
d.next_bits = 0;
}
/// Reads first 7 bits, and then maybe 1 or 2 more to get full 7,8 or 9 bit code.
/// ref: https://datatracker.ietf.org/doc/html/rfc1951#page-12
/// Lit Value Bits Codes