Function decode [src]

Decode a literals section header.
Prototype

pub fn decode(in: *Reader, remaining: *Limit) !Header
Parameters

in: *Readerremaining: *Limit
Source

  pub fn decode(in: *Reader, remaining: *Limit) !Header {
    remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
    const byte0 = try in.takeByte();
    const block_type: BlockType = @enumFromInt(byte0 & 0b11);
    const size_format: u2 = @intCast((byte0 & 0b1100) >> 2);
    var regenerated_size: u20 = undefined;
    var compressed_size: ?u18 = null;
    switch (block_type) {
        .raw, .rle => {
            switch (size_format) {
                0, 2 => {
                    regenerated_size = byte0 >> 3;
                },
                1 => {
                    remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
                    regenerated_size = (byte0 >> 4) + (@as(u20, try in.takeByte()) << 4);
                },
                3 => {
                    remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
                    regenerated_size = (byte0 >> 4) +
                        (@as(u20, try in.takeByte()) << 4) +
                        (@as(u20, try in.takeByte()) << 12);
                },
            }
        },
        .compressed, .treeless => {
            remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
            const byte1 = try in.takeByte();
            const byte2 = try in.takeByte();
            switch (size_format) {
                0, 1 => {
                    regenerated_size = (byte0 >> 4) + ((@as(u20, byte1) & 0b00111111) << 4);
                    compressed_size = ((byte1 & 0b11000000) >> 6) + (@as(u18, byte2) << 2);
                },
                2 => {
                    remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
                    const byte3 = try in.takeByte();
                    regenerated_size = (byte0 >> 4) + (@as(u20, byte1) << 4) + ((@as(u20, byte2) & 0b00000011) << 12);
                    compressed_size = ((byte2 & 0b11111100) >> 2) + (@as(u18, byte3) << 6);
                },
                3 => {
                    remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
                    const byte3 = try in.takeByte();
                    const byte4 = try in.takeByte();
                    regenerated_size = (byte0 >> 4) + (@as(u20, byte1) << 4) + ((@as(u20, byte2) & 0b00111111) << 12);
                    compressed_size = ((byte2 & 0b11000000) >> 6) + (@as(u18, byte3) << 2) + (@as(u18, byte4) << 10);
                },
            }
        },
    }
    return .{
        .block_type = block_type,
        .size_format = size_format,
        .regenerated_size = regenerated_size,
        .compressed_size = compressed_size,
    };
}  