struct Header [src]

Fields

block_type: BlockType
size_format: u2
regenerated_size: u20
compressed_size: ?u18
Members

decode (Function)
Source

  pub const Header = struct {
    block_type: BlockType,
    size_format: u2,
    regenerated_size: u20,
    compressed_size: ?u18,

    /// Decode a literals section header.
    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,
        };
    }
}  