1 files changed, 69 insertions, 0 deletions
diff --git a/theories/Numbers/AltBinNotations.v b/theories/Numbers/AltBinNotations.v
new file mode 100644
index 00000000..c7e39996
--- /dev/null
+++ b/theories/Numbers/AltBinNotations.v
@@ -0,0 +1,69 @@
+(************************************************************************)
+(*         *   The Coq Proof Assistant / The Coq Development Team       *)
+(*  v      *   INRIA, CNRS and contributors - Copyright 1999-2018       *)
+(* <O___,, *       (see CREDITS file for the list of authors)           *)
+(*   \VV/  **************************************************************)
+(*    //   *    This file is distributed under the terms of the         *)
+(*         *     GNU Lesser General Public License Version 2.1          *)
+(*         *     (see LICENSE file for the text of the license)         *)
+(************************************************************************)
+
+(** * Alternative Binary Numeral Notations *)
+
+(** Faster but less safe parsers and printers of [positive], [N], [Z]. *)
+
+(** By default, literals in types [positive], [N], [Z] are parsed and
+    printed via the [Numeral Notation] command, by conversion from/to
+    the [Decimal.int] representation. When working with numbers with
+    thousands of digits and more, conversion from/to [Decimal.int] can
+    become significantly slow. If that becomes a problem for your
+    development, this file provides some alternative [Numeral
+    Notation] commmands that use [Z] as bridge type. To enable these
+    commands, just be sure to [Require] this file after other files
+    defining numeral notations.
+
+    Note: up to Coq 8.8, literals in types [positive], [N], [Z] were
+    parsed and printed using a native ML library of arbitrary
+    precision integers named bigint.ml. From 8.9, the default is to
+    parse and print using a Coq library converting sequences of
+    digits, hence reducing the amount of ML code to trust. But this
+    method is slower. This file then gives access to the legacy
+    method, trading efficiency against a larger ML trust base relying
+    on bigint.ml. *)
+
+Require Import BinNums.
+
+(** [positive] *)
+
+Definition pos_of_z z :=
+  match z with
+    | Zpos p => Some p
+    | _ => None
+  end.
+
+Definition pos_to_z p := Zpos p.
+
+Numeral Notation positive pos_of_z pos_to_z : positive_scope.
+
+(** [N] *)
+
+Definition n_of_z z :=
+  match z with
+    | Z0 => Some N0
+    | Zpos p => Some (Npos p)
+    | Zneg _ => None
+  end.
+
+Definition n_to_z n :=
+ match n with
+   | N0 => Z0
+   | Npos p => Zpos p
+ end.
+
+Numeral Notation N n_of_z n_to_z : N_scope.
+
+(** [Z] *)
+
+Definition z_of_z (z:Z) := z.
+
+Numeral Notation Z z_of_z z_of_z : Z_scope.