Function encode [src]

Encode a length according to NIST SP 800-185.

Prototype

pub fn encode(comptime encoding: NistLengthEncoding, len: usize) Length

Parameters

encoding: NistLengthEncodinglen: usize

Source

  pub fn encode(comptime encoding: NistLengthEncoding, len: usize) Length {
    const len_bits = @bitSizeOf(@TypeOf(len)) - @clz(len) + 3;
    const len_bytes = std.math.divCeil(usize, len_bits, 8) catch unreachable;

    var res = Length{ .len = len_bytes + 1 };
    if (encoding == .right) {
        res.buf[len_bytes] = @intCast(len_bytes);
    }
    const end = if (encoding == .right) len_bytes - 1 else len_bytes;
    res.buf[end] = @truncate(len << 3);
    var len_ = len >> 5;
    for (1..len_bytes) |i| {
        res.buf[end - i] = @truncate(len_);
        len_ >>= 8;
    }
    if (encoding == .left) {
        res.buf[0] = @intCast(len_bytes);
    }
    return res;
}  