Function safe_arch::bit_extract_u64

#[must_use]pub fn bit_extract_u64(a: u64, start: u32, len: u32) -> u64

This is supported with target feature bmi1 only.

Extract a span of bits from the u64, start and len style.

assert_eq!(bit_extract_u64(0b0110, 0, 3), 0b110);
assert_eq!(bit_extract_u64(0b0110, 0, 2), 0b10);
assert_eq!(bit_extract_u64(0b0110, 1, 2), 0b11);