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+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(** Extraction of [positive], [N] and [Z] into Ocaml's [int] *)
+
+Require Import ZArith NArith ZOdiv_def.
+Require Import ExtrOcamlBasic.
+
+(** Disclaimer: trying to obtain efficient certified programs
+    by extracting [Z] into [int] is definitively *not* a good idea.
+    See the Disclaimer in [ExtrOcamlNatInt]. *)
+
+(** Mapping of [positive], [Z], [N] into [int]. The last strings
+    emulate the matching, see documentation of [Extract Inductive]. *)
+
+Extract Inductive positive => int
+[ "(fun p->1+2*p)" "(fun p->2*p)" "1" ]
+"(fun f2p1 f2p f1 p ->
+  if p<=1 then f1 () else if p mod 2 = 0 then f2p (p/2) else f2p1 (p/2))".
+
+Extract Inductive Z => int [ "0" "" "(~-)" ]
+"(fun f0 fp fn z -> if z=0 then f0 () else if z>0 then fp z else fn (-z))".
+
+Extract Inductive N => int [ "0" "" ]
+"(fun f0 fp n -> if n=0 then f0 () else fp n)".
+
+(** Nota: the "" above is used as an identity function "(fun p->p)" *)
+
+(** Efficient (but uncertified) versions for usual functions *)
+
+Extract Constant Pplus => "(+)".
+Extract Constant Psucc => "succ".
+Extract Constant Ppred => "fun n -> max 1 (n-1)".
+Extract Constant Pminus => "fun n m -> max 1 (n-m)".
+Extract Constant Pmult => "( * )".
+Extract Constant Pmin => "min".
+Extract Constant Pmax => "max".
+Extract Constant Pcompare =>
+ "fun x y c -> if x=y then c else if x<y then Lt else Gt".
+
+
+Extract Constant Nplus => "(+)".
+Extract Constant Nsucc => "succ".
+Extract Constant Npred => "fun n -> max 0 (n-1)".
+Extract Constant Nminus => "fun n m -> max 0 (n-m)".
+Extract Constant Nmult => "( * )".
+Extract Constant Nmin => "min".
+Extract Constant Nmax => "max".
+Extract Constant Ndiv => "fun a b -> if b=0 then 0 else a/b".
+Extract Constant Nmod => "fun a b -> if b=0 then a else a mod b".
+Extract Constant Ncompare =>
+ "fun x y -> if x=y then Eq else if x<y then Lt else Gt".
+
+
+Extract Constant Zplus => "(+)".
+Extract Constant Zsucc => "succ".
+Extract Constant Zpred => "pred".
+Extract Constant Zminus => "(-)".
+Extract Constant Zmult => "( * )".
+Extract Constant Zopp => "(~-)".
+Extract Constant Zabs => "abs".
+Extract Constant Zmin => "min".
+Extract Constant Zmax => "max".
+Extract Constant Zcompare =>
+ "fun x y -> if x=y then Eq else if x<y then Lt else Gt".
+
+Extract Constant Z_of_N => "fun p -> p".
+Extract Constant Zabs_N => "abs".
+
+(** Zdiv and Zmod are quite complex to define in terms of (/) and (mod).
+    For the moment we don't even try *)
+
+