Function set_bits25 

pub unsafe fn set_bits25(
    ptr: *mut u8,
    first_bit: usize,
    value: u32,
    len_mask: u32,
)

Write desired number, at most 25 lowest value bits to ptr, beginning from first_bit, using bit-or operation. Before write, appropriate fragment of buffer is zeroed by bit-andn with len_mask (which should be of type 0..01..1, with desired number of bit ones). The most significant bits of value should be zeros.