srctree

Igor Anić parent 8a963fd6 71128160
flate: option to fill BitReader

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

inline split

lib/std/compress/flate/bit_reader.zig added: 60, removed: 3, total 57

@@ -56,7 +56,7 @@ pub fn BitReader(T: type, comptime ReaderType: type) type {

/// that number of bits available. If end of forward stream is reached

/// it may be some extra zero bits in buffer.

pub inline fn fill(self: *Self, nice: u6) !void {

if (self.nbits >= nice) {

if (self.nbits >= nice and nice != 0) {

return; // We have enought bits

}

// Read more bits from forward reader

@@ -115,7 +115,7 @@ pub fn BitReader(T: type, comptime ReaderType: type) type {

assert(how == 0);

assert(self.alignBits() == 0);

try self.fill(@bitSizeOf(T));

assert(self.nbits == @bitSizeOf(T));

if (self.nbits != @bitSizeOf(T)) return error.EndOfStream;

const v = self.bits;

self.nbits = 0;

self.bits = 0;

@@ -363,3 +363,60 @@ test "readFixedCode" {

try testing.expect(rdr.nbits == 0);

}

test "u32 leaves no bits on u32 reads" {

const data = [_]u8{

0xff, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,

0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,

};

var fbs = std.io.fixedBufferStream(&data);

var br = bitReader(u32, fbs.reader());

_ = try br.read(u3);

try testing.expectEqual(29, br.nbits);

br.alignToByte();

try testing.expectEqual(24, br.nbits);

try testing.expectEqual(0x04_03_02_01, try br.read(u32));

try testing.expectEqual(0, br.nbits);

try testing.expectEqual(0x08_07_06_05, try br.read(u32));

try testing.expectEqual(0, br.nbits);

_ = try br.read(u9);

try testing.expectEqual(23, br.nbits);

br.alignToByte();

try testing.expectEqual(16, br.nbits);

try testing.expectEqual(0x0e_0d_0c_0b, try br.read(u32));

try testing.expectEqual(0, br.nbits);

}

test "u64 need fill after alignToByte" {

const data = [_]u8{

0xff, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,

0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,

};

// without fill

var fbs = std.io.fixedBufferStream(&data);

var br = bitReader(u64, fbs.reader());

_ = try br.read(u23);

try testing.expectEqual(41, br.nbits);

br.alignToByte();

try testing.expectEqual(40, br.nbits);

try testing.expectEqual(0x06_05_04_03, try br.read(u32));

try testing.expectEqual(8, br.nbits);

try testing.expectEqual(0x0a_09_08_07, try br.read(u32));

try testing.expectEqual(32, br.nbits);

// fill after align ensures all bits filled

fbs.reset();

br = bitReader(u64, fbs.reader());

_ = try br.read(u23);

try testing.expectEqual(41, br.nbits);

br.alignToByte();

try br.fill(0);

try testing.expectEqual(64, br.nbits);

try testing.expectEqual(0x06_05_04_03, try br.read(u32));

try testing.expectEqual(32, br.nbits);

try testing.expectEqual(0x0a_09_08_07, try br.read(u32));

try testing.expectEqual(0, br.nbits);

}