Commit 711281602a

Igor Anić <igor.anic@gmail.com>
2024-03-02 23:20:02
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.
master
1 parent 8a963fd
Changed files (1)
lib
std
compress
flate
bit_reader.zig
lib/std/compress/flate/bit_reader.zig
@@ -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);
+}