authorgravatar for andrew@ziglang.orgAndrew Kelley <andrew@ziglang.org> 2025-07-28 21:05:33-07:00
committergravatar for andrew@ziglang.orgAndrew Kelley <andrew@ziglang.org> 2025-07-31 22:10:11-07:00
log2569f4ff8514f47730c1abd42691f8fc1cdd22d5
treeeee17566aac40aef7f0ba12a44869bc7d42bdbc0
parent5bc63794cc9f38801e674d306c2c9ef4ccf92f13

simplify tossBitsEnding

1 files changed, 30 insertions(+), 18 deletions(-)

lib/std/compress/flate/Decompress.zig+30-18
......@@ -219,7 +219,7 @@ fn readInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader.S
219219 const block_type: BlockType = @enumFromInt(try d.takeBits(u2));
220220 switch (block_type) {
221221 .stored => {
222 d.alignBitsToByte(); // skip padding until byte boundary
222 d.alignBitsDiscarding();
223223 // everything after this is byte aligned in stored block
224224 const len = try in.takeInt(u16, .little);
225225 const nlen = try in.takeInt(u16, .little);
......@@ -333,20 +333,23 @@ fn readInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader.S
333333 return @intFromEnum(limit) - remaining;
334334 },
335335 .protocol_footer => {
336 d.alignBitsToByte();
337336 switch (d.container_metadata) {
338337 .gzip => |*gzip| {
338 d.alignBitsDiscarding();
339339 gzip.* = .{
340340 .crc = try in.takeInt(u32, .little),
341341 .count = try in.takeInt(u32, .little),
342342 };
343343 },
344344 .zlib => |*zlib| {
345 d.alignBitsDiscarding();
345346 zlib.* = .{
346347 .adler = try in.takeInt(u32, .little),
347348 };
348349 },
349 .raw => {},
350 .raw => {
351 d.alignBitsPreserving();
352 },
350353 }
351354 d.state = .end;
352355 return 0;
......@@ -475,22 +478,16 @@ fn tossBits(d: *Decompress, n: u6) !void {
475478fn tossBitsEnding(d: *Decompress, n: u6) !void {
476479 const remaining_bits = d.remaining_bits;
477480 const in = d.input;
478 var remaining_needed_bits = n - remaining_bits;
479 while (remaining_needed_bits >= 8) {
480 try in.discardAll(1);
481 remaining_needed_bits -= 8;
482 }
483 if (remaining_needed_bits == 0) {
484 d.next_bits = 0;
485 d.remaining_bits = 0;
486 return;
487 }
488 const byte = in.takeByte() catch |err| switch (err) {
481 const buffered_n = in.bufferedLen();
482 if (buffered_n == 0) return error.EndOfStream;
483 assert(buffered_n < @sizeOf(usize));
484 const needed_bits = n - remaining_bits;
485 const next_int = in.takeVarInt(usize, .little, buffered_n) catch |err| switch (err) {
489486 error.ReadFailed => return error.ReadFailed,
490 error.EndOfStream => if (remaining_bits == 0) return error.EndOfStream else 0,
487 error.EndOfStream => unreachable,
491488 };
492 d.next_bits = @as(usize, byte) >> remaining_needed_bits;
493 d.remaining_bits = @intCast(8 - remaining_needed_bits);
489 d.next_bits = next_int >> needed_bits;
490 d.remaining_bits = @intCast(@as(usize, n) * 8 -| @as(usize, needed_bits));
494491}
495492
496493fn takeBitsRuntime(d: *Decompress, n: u4) !u16 {
......@@ -501,7 +498,7 @@ fn takeBitsRuntime(d: *Decompress, n: u4) !u16 {
501498 return u;
502499}
503500
504fn alignBitsToByte(d: *Decompress) void {
501fn alignBitsDiscarding(d: *Decompress) void {
505502 const remaining_bits = d.remaining_bits;
506503 const next_bits = d.next_bits;
507504 if (remaining_bits == 0) return;
......@@ -518,6 +515,21 @@ fn alignBitsToByte(d: *Decompress) void {
518515 d.next_bits = 0;
519516}
520517
518fn alignBitsPreserving(d: *Decompress) void {
519 const remaining_bits: usize = d.remaining_bits;
520 if (remaining_bits == 0) return;
521 const n_bytes = (remaining_bits + 7) / 8;
522 const in = d.input;
523 in.seek -= n_bytes;
524 var put_back_bits = d.next_bits;
525 for (in.buffer[in.seek..][0..n_bytes]) |*b| {
526 b.* = @truncate(put_back_bits);
527 put_back_bits >>= 8;
528 }
529 d.remaining_bits = 0;
530 d.next_bits = 0;
531}
532
521533/// Reads first 7 bits, and then maybe 1 or 2 more to get full 7,8 or 9 bit code.
522534/// ref: https://datatracker.ietf.org/doc/html/rfc1951#page-12
523535/// Lit Value Bits Codes