+redef class Byte
+ # Write self as a string into `ns` at position `pos`
+ private fun add_digest_at(ns: NativeString, pos: Int) do
+ var tmp = (0xF0u8 & self) >> 4
+ ns[pos] = if tmp >= 0x0Au8 then tmp + 0x37u8 else tmp + 0x30u8
+ tmp = 0x0Fu8 & self
+ ns[pos + 1] = if tmp >= 0x0Au8 then tmp + 0x37u8 else tmp + 0x30u8
+ end
+
+ # Is `self` a valid hexadecimal digit (in ASCII)
+ #
+ # ~~~nit
+ # intrude import core::bytes
+ # assert not '/'.ascii.to_b.is_valid_hexdigit
+ # assert '0'.ascii.to_b.is_valid_hexdigit
+ # assert '9'.ascii.to_b.is_valid_hexdigit
+ # assert not ':'.ascii.to_b.is_valid_hexdigit
+ # assert not '@'.ascii.to_b.is_valid_hexdigit
+ # assert 'A'.ascii.to_b.is_valid_hexdigit
+ # assert 'F'.ascii.to_b.is_valid_hexdigit
+ # assert not 'G'.ascii.to_b.is_valid_hexdigit
+ # assert not '`'.ascii.to_b.is_valid_hexdigit
+ # assert 'a'.ascii.to_b.is_valid_hexdigit
+ # assert 'f'.ascii.to_b.is_valid_hexdigit
+ # assert not 'g'.ascii.to_b.is_valid_hexdigit
+ # ~~~
+ private fun is_valid_hexdigit: Bool do
+ return (self >= 0x30u8 and self <= 0x39u8) or
+ (self >= 0x41u8 and self <= 0x46u8) or
+ (self >= 0x61u8 and self <= 0x66u8)
+ end
+
+ # `self` as a hexdigit to its byte value
+ #
+ # ~~~nit
+ # intrude import core::bytes
+ # assert 0x39u8.hexdigit_to_byteval == 0x09u8
+ # assert 0x43u8.hexdigit_to_byteval == 0x0Cu8
+ # ~~~
+ #
+ # REQUIRE: `self.is_valid_hexdigit`
+ private fun hexdigit_to_byteval: Byte do
+ if self >= 0x30u8 and self <= 0x39u8 then
+ return self - 0x30u8
+ else if self >= 0x41u8 and self <= 0x46u8 then
+ return self - 0x37u8
+ else if self >= 0x61u8 and self <= 0x66u8 then
+ return self - 0x57u8
+ end
+ # Happens only if the requirement is not met.
+ # i.e. this abort is here to please the compiler
+ abort
+ end
+end
+