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let is_pow_2 n = n land (n - 1) = 0
let max_0 n =
let m = n asr (Sys.int_size - 1) in
n land lnot m
let ceil_pow_2_minus_1 n =
let n = n lor (n lsr 1) in
let n = n lor (n lsr 2) in
let n = n lor (n lsr 4) in
let n = n lor (n lsr 8) in
let n = n lor (n lsr 16) in
if Sys.int_size > 32 then n lor (n lsr 32) else n
let ceil_pow_2 n =
if n <= 1 then 1
else
let n = n - 1 in
let n = ceil_pow_2_minus_1 n in
n + 1