std.bytes

API summary (generated from the Beans source by npm run coverage): 6 package functions.

std.bytes adds a CRC-32 checksum and unsigned varint helpers on top of the builtin Bytes buffer. It is written in Beans; read it at stdlib/std/bytes/bytes.b.

import std.bytes

A varint is a compact way to store an integer, using fewer bytes for small values. The unsigned form here is LEB128.

Checksum

pub fn crc32(data: Bytes) -> u32

• crc32 is the IEEE CRC-32 checksum, using polynomial 0xedb88320.

Unsigned varints

pub fn uvarint_size(value: u64) -> int
pub fn encode_uvarint(value: u64) -> Bytes
pub fn append_uvarint(data: Bytes, value: u64)
pub fn decode_uvarint(data: Bytes) -> Option<u64>
pub fn decode_uvarint_at_or(data: Bytes, start: int, fallback: u64) -> u64

• uvarint_size reports how many bytes value needs as an unsigned varint.
• encode_uvarint returns a new buffer holding value as an unsigned varint.
• append_uvarint appends value as a varint to data in place and returns nothing.
• decode_uvarint reads a varint from the start of data. It returns none if the data is truncated or the value overflows 64 bits, and it reads at most 10 bytes.
• decode_uvarint_at_or reads a varint starting at start. It returns fallback when start is out of range, or when the value is truncated or overflows.

import std.io
import std.bytes

fn main() {
    let buf: Bytes = bytes.encode_uvarint(300)
    io.println(buf.len())                       // 2
    let value: Option<u64> = bytes.decode_uvarint(buf)
    io.println(value)                            // some(300)
    io.println(bytes.crc32(Bytes.from("hello")))
}

See also

• Bytes, the buffer type, which also has its own crc32 and append_uvarint methods.
• std.encoding.binary, a fuller set of fixed-width and varint reads and writes.