+
+ # A signed big-endian representation of `self`
+ #
+ # ~~~
+ # assert 1.to_bytes.hexdigest == "01"
+ # assert 255.to_bytes.hexdigest == "FF"
+ # assert 256.to_bytes.hexdigest == "0100"
+ # assert 65535.to_bytes.hexdigest == "FFFF"
+ # assert 65536.to_bytes.hexdigest == "010000"
+ # ~~~
+ #
+ # Negative values are converted to their two's complement.
+ # Be careful as the result can be ambiguous.
+ #
+ # ~~~
+ # assert (-1).to_bytes.hexdigest == "FF"
+ # assert (-32).to_bytes.hexdigest == "E0"
+ # assert (-512).to_bytes.hexdigest == "FE00"
+ # assert (-65794).to_bytes.hexdigest == "FEFEFE"
+ # ~~~
+ #
+ # Optionally, set `n_bytes` to the desired number of bytes in the output.
+ # This setting can disambiguate the result between positive and negative
+ # integers. Be careful with this parameter as the result may overflow.
+ #
+ # ~~~
+ # assert 1.to_bytes(2).hexdigest == "0001"
+ # assert 65535.to_bytes(2).hexdigest == "FFFF"
+ # assert (-1).to_bytes(2).hexdigest == "FFFF"
+ # assert (-512).to_bytes(4).hexdigest == "FFFFFE00"
+ # assert 0x123456.to_bytes(2).hexdigest == "3456"
+ # ~~~
+ #
+ # For 0, a Bytes object with single nul byte is returned (instead of an empty Bytes object).
+ #
+ # ~~~
+ # assert 0.to_bytes.hexdigest == "00"
+ # ~~~
+ #
+ # For positive integers, `Bytes::to_i` can reverse the operation.
+ #
+ # ~~~
+ # assert 1234.to_bytes.to_i == 1234
+ # ~~~
+ #
+ # Require self >= 0
+ fun to_bytes(n_bytes: nullable Int): Bytes do
+
+ # If 0, force using at least one byte
+ if self == 0 and n_bytes == null then n_bytes = 1
+
+ # Compute the len (log256)
+ var len = 1
+ var max = 256
+ var s = self.abs
+ while s >= max do
+ len += 1
+ max *= 256
+ end
+
+ # Two's complement
+ s = self
+ if self < 0 then
+ var ff = 0
+ for j in [0..len[ do
+ ff *= 0x100
+ ff += 0xFF
+ end
+
+ s = ((-self) ^ ff) + 1
+ end
+
+ # Cut long values
+ if n_bytes != null and len > n_bytes then len = n_bytes
+
+ # Allocate the buffer
+ var cap = n_bytes or else len
+ var res = new Bytes.with_capacity(cap)
+
+ var filler = if self < 0 then 0xFF else 0
+ for i in [0..cap[ do res[i] = filler
+
+ # Fill it starting with the end
+ var i = cap
+ var sum = s
+ while i > cap - len do
+ i -= 1
+ res[i] = sum % 256
+ sum /= 256
+ end
+
+ return res
+ end