To convert between Rug and bitvec types, the bit order, endianness, and limb
size need to correspond:
In the GMP mpz_import function, which Rug calls in Integer::from_digits, it
converts the input data to its internal format, which is Lsf. If the input
order is Lsf* and the endianness matches the host, the data is simply copied.
If the input endianness does not match the host, the bytes are swapped. If the
input order is Msf*, the bits are reversed.
bitvec strongly recommends using Lsb0 as the BitOrder, even if it doesn’t
match the host endianness, because it provides the best codegen for bit
manipulation. Since there is no equivalent to Lsf in bitvec and big-endian
systems are rare, LsfLe/Lsb0 is the best option.
Whitespace integers are big endian, but are parsed and pushed to a BitVec in
little-endian order, so the slice of bits needs to be reversed (i.e., not
reversing or swapping words) before converting to an Integer.
GMP uses a machine word as the limb size and bitvec uses usize as the
default BitStore.
| Rug | bitvec | Bit order | Endianness |
|---|---|---|---|
Lsf |
least-significant bit first | host endianness | |
LsfLe |
Lsb0 |
least-significant bit first | little-endian |
LsfBe |
least-significant bit first | big-endian | |
Msf |
most-significant bit first | host endianness | |
MsfLe |
most-significant bit first | little-endian | |
MsfBe |
Msb0 |
most-significant bit first | big-endian |
LocalBits |
alias to Lsb0 or Msb0 | host endianness |