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why3/examples/locate_max.mlw
2022-05-11 17:46:27 +02:00

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(** Simple example to illustrate the C memory model *)
use int.Int
use map.Map as Map
use mach.c.C
use mach.int.Int32
use mach.int.Int64
function ([]) (a: ptr 'a) (i: int): 'a = Map.get a.data.Array.elts (a.offset + i)
let locate_max (a: ptr int64) (n: int32): int32
requires { 0 < n }
requires { valid a n }
ensures { 0 <= result < n }
ensures { forall i. 0 <= i < n -> a[i] <= a[result] }
= let ref idx = 0 in
for j = 1 to n - 1 do
invariant { 0 <= idx < n }
invariant { forall i. 0 <= i < j -> a[i] <= a[idx] }
if get_ofs a idx < get_ofs a j then idx <- j
done;
idx