Function croaring_sys::roaring_bitmap_get_index

pub unsafe extern "C" fn roaring_bitmap_get_index(
    r: *const roaring_bitmap_t,
    x: u32
) -> i64

Returns the index of x in the given roaring bitmap. If the roaring bitmap doesn’t contain x , this function will return -1. The difference with rank function is that this function will return -1 when x is not the element of roaring bitmap, but the rank function will return a non-negative number.