Integer logarithm
The base-2 integer logarithm can be computed by counting the number
of leading zero bits in the integer, through the clz builtin
function. For example for 64-bit integers:
def ilog2 (n: i64) : i64 = i64.i32 (63 - i64.clz n)> ilog2 1276i64> ilog2 1287i64