struct LzCircularBuffer [src]

A circular buffer for LZ sequences

Fields

buf: ArrayListUnmanaged(u8)Circular buffer

dict_size: usizeLength of the buffer

memlimit: usizeBuffer memory limit

cursor: usizeCurrent position

len: usizeTotal number of bytes sent through the buffer

Members

appendLiteral (Function)
appendLz (Function)
deinit (Function)
finish (Function)
get (Function)
init (Function)
lastN (Function)
lastOr (Function)
set (Function)

Source

  pub const LzCircularBuffer = struct {
    /// Circular buffer
    buf: ArrayListUnmanaged(u8),

    /// Length of the buffer
    dict_size: usize,

    /// Buffer memory limit
    memlimit: usize,

    /// Current position
    cursor: usize,

    /// Total number of bytes sent through the buffer
    len: usize,

    const Self = @This();

    pub fn init(dict_size: usize, memlimit: usize) Self {
        return Self{
            .buf = .{},
            .dict_size = dict_size,
            .memlimit = memlimit,
            .cursor = 0,
            .len = 0,
        };
    }

    pub fn get(self: Self, index: usize) u8 {
        return if (0 <= index and index < self.buf.items.len)
            self.buf.items[index]
        else
            0;
    }

    pub fn set(self: *Self, allocator: Allocator, index: usize, value: u8) !void {
        if (index >= self.memlimit) {
            return error.CorruptInput;
        }
        try self.buf.ensureTotalCapacity(allocator, index + 1);
        while (self.buf.items.len < index) {
            self.buf.appendAssumeCapacity(0);
        }
        self.buf.appendAssumeCapacity(value);
    }

    /// Retrieve the last byte or return a default
    pub fn lastOr(self: Self, lit: u8) u8 {
        return if (self.len == 0)
            lit
        else
            self.get((self.dict_size + self.cursor - 1) % self.dict_size);
    }

    /// Retrieve the n-th last byte
    pub fn lastN(self: Self, dist: usize) !u8 {
        if (dist > self.dict_size or dist > self.len) {
            return error.CorruptInput;
        }

        const offset = (self.dict_size + self.cursor - dist) % self.dict_size;
        return self.get(offset);
    }

    /// Append a literal
    pub fn appendLiteral(
        self: *Self,
        allocator: Allocator,
        lit: u8,
        writer: anytype,
    ) !void {
        try self.set(allocator, self.cursor, lit);
        self.cursor += 1;
        self.len += 1;

        // Flush the circular buffer to the output
        if (self.cursor == self.dict_size) {
            try writer.writeAll(self.buf.items);
            self.cursor = 0;
        }
    }

    /// Fetch an LZ sequence (length, distance) from inside the buffer
    pub fn appendLz(
        self: *Self,
        allocator: Allocator,
        len: usize,
        dist: usize,
        writer: anytype,
    ) !void {
        if (dist > self.dict_size or dist > self.len) {
            return error.CorruptInput;
        }

        var offset = (self.dict_size + self.cursor - dist) % self.dict_size;
        var i: usize = 0;
        while (i < len) : (i += 1) {
            const x = self.get(offset);
            try self.appendLiteral(allocator, x, writer);
            offset += 1;
            if (offset == self.dict_size) {
                offset = 0;
            }
        }
    }

    pub fn finish(self: *Self, writer: anytype) !void {
        if (self.cursor > 0) {
            try writer.writeAll(self.buf.items[0..self.cursor]);
            self.cursor = 0;
        }
    }

    pub fn deinit(self: *Self, allocator: Allocator) void {
        self.buf.deinit(allocator);
        self.* = undefined;
    }
}  