Commit 711281602a0efdd3b194c0419e8bccc2bb399167 | zig

author	Igor Anić <igor.anic@gmail.com> 2024-03-02 23:20:02+01:00
committer	Igor Anić <igor.anic@gmail.com> 2024-03-04 09:53:01+01:00
log	711281602a0efdd3b194c0419e8bccc2bb399167
tree	28640cc1a1a714fa2bd0e8c6abcafcd22646768a
parent	8a963fd66e22820119bac1b0a568f0cf3af4fa8e

flate: option to fill BitReader

fill(0) will fill all bytes in bit reader. If bit reader is aligned to
the byte, as it is at the end of the stream this ensures no overshoot
when reading footer. Footer is 4 bytes (zlib) or 8 bytes (gzip). For
zlib we will use 4 bytes BitReader and 8 for gzip. After align and fill
we will read those bytes and leave BitReader empty after that.

1 files changed, 59 insertions(+), 2 deletions(-)

lib
- std
  - compress
    flate
    bit_reader.zig

lib/std/compress/flate/bit_reader.zig+59-2

...	...	@@ -56,7 +56,7 @@ pub fn BitReader(T: type, comptime ReaderType: type) type {
56	56	/// that number of bits available. If end of forward stream is reached
57	57	/// it may be some extra zero bits in buffer.
58	58	pub inline fn fill(self: *Self, nice: u6) !void {
59		if (self.nbits >= nice) {
	59	if (self.nbits >= nice and nice != 0) {
60	60	return; // We have enought bits
61	61	}
62	62	// Read more bits from forward reader
...	...	@@ -115,7 +115,7 @@ pub fn BitReader(T: type, comptime ReaderType: type) type {
115	115	assert(how == 0);
116	116	assert(self.alignBits() == 0);
117	117	try self.fill(@bitSizeOf(T));
118		assert(self.nbits == @bitSizeOf(T));
	118	if (self.nbits != @bitSizeOf(T)) return error.EndOfStream;
119	119	const v = self.bits;
120	120	self.nbits = 0;
121	121	self.bits = 0;
...	...	@@ -363,3 +363,60 @@ test "readFixedCode" {
363	363	try testing.expect(rdr.nbits == 0);
364	364	}
365	365	}
	366
	367	test "u32 leaves no bits on u32 reads" {
	368	const data = [_]u8{
	369	0xff, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
	370	0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
	371	};
	372	var fbs = std.io.fixedBufferStream(&data);
	373	var br = bitReader(u32, fbs.reader());
	374
	375	_ = try br.read(u3);
	376	try testing.expectEqual(29, br.nbits);
	377	br.alignToByte();
	378	try testing.expectEqual(24, br.nbits);
	379	try testing.expectEqual(0x04_03_02_01, try br.read(u32));
	380	try testing.expectEqual(0, br.nbits);
	381	try testing.expectEqual(0x08_07_06_05, try br.read(u32));
	382	try testing.expectEqual(0, br.nbits);
	383
	384	_ = try br.read(u9);
	385	try testing.expectEqual(23, br.nbits);
	386	br.alignToByte();
	387	try testing.expectEqual(16, br.nbits);
	388	try testing.expectEqual(0x0e_0d_0c_0b, try br.read(u32));
	389	try testing.expectEqual(0, br.nbits);
	390	}
	391
	392	test "u64 need fill after alignToByte" {
	393	const data = [_]u8{
	394	0xff, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
	395	0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
	396	};
	397
	398	// without fill
	399	var fbs = std.io.fixedBufferStream(&data);
	400	var br = bitReader(u64, fbs.reader());
	401	_ = try br.read(u23);
	402	try testing.expectEqual(41, br.nbits);
	403	br.alignToByte();
	404	try testing.expectEqual(40, br.nbits);
	405	try testing.expectEqual(0x06_05_04_03, try br.read(u32));
	406	try testing.expectEqual(8, br.nbits);
	407	try testing.expectEqual(0x0a_09_08_07, try br.read(u32));
	408	try testing.expectEqual(32, br.nbits);
	409
	410	// fill after align ensures all bits filled
	411	fbs.reset();
	412	br = bitReader(u64, fbs.reader());
	413	_ = try br.read(u23);
	414	try testing.expectEqual(41, br.nbits);
	415	br.alignToByte();
	416	try br.fill(0);
	417	try testing.expectEqual(64, br.nbits);
	418	try testing.expectEqual(0x06_05_04_03, try br.read(u32));
	419	try testing.expectEqual(32, br.nbits);
	420	try testing.expectEqual(0x0a_09_08_07, try br.read(u32));
	421	try testing.expectEqual(0, br.nbits);
	422	}