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+------------------------------------------------------------------------------
+-- --
+-- GNAT COMPILER COMPONENTS --
+-- --
+-- S Y S T E M . B I G N U M S --
+-- --
+-- S p e c --
+-- --
+-- Copyright (C) 2012, Free Software Foundation, Inc. --
+-- --
+-- GNAT is free software; you can redistribute it and/or modify it under --
+-- terms of the GNU General Public License as published by the Free Soft- --
+-- ware Foundation; either version 3, or (at your option) any later ver- --
+-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
+-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
+-- or FITNESS FOR A PARTICULAR PURPOSE. --
+-- --
+-- As a special exception under Section 7 of GPL version 3, you are granted --
+-- additional permissions described in the GCC Runtime Library Exception, --
+-- version 3.1, as published by the Free Software Foundation. --
+-- --
+-- You should have received a copy of the GNU General Public License and --
+-- a copy of the GCC Runtime Library Exception along with this program; --
+-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
+-- <http://www.gnu.org/licenses/>. --
+-- --
+-- GNAT was originally developed by the GNAT team at New York University. --
+-- Extensive contributions were provided by Ada Core Technologies Inc. --
+-- --
+------------------------------------------------------------------------------
+
+-- This package provides arbitrary precision signed integer arithmetic for
+-- use in computing intermediate values in expressions for the case where
+-- pragma Overflow_Check (Eliminated) is in effect.
+
+with Interfaces;
+
+package System.Bignums is
+
+ pragma Assert (Long_Long_Integer'Size = 64);
+ -- This package assumes that Long_Long_Integer size is 64 bit (i.e. that it
+ -- has a range of -2**63 to 2**63-1). The front end ensures that the mode
+ -- ELIMINATED is not allowed for overflow checking if this is not the case.
+
+ subtype Length is Natural range 0 .. 2 ** 23 - 1;
+ -- Represent number of words in Digit_Vector
+
+ Base : constant := 2 ** 32;
+ -- Digit vectors use this base
+
+ subtype SD is Interfaces.Unsigned_32;
+ -- Single length digit
+
+ type Digit_Vector is array (Length range <>) of SD;
+ -- Represent digits of a number (most significant digit first)
+
+ type Bignum_Data (Len : Length) is record
+ Neg : Boolean;
+ -- Set if value is negative, never set for zero
+
+ D : Digit_Vector (1 .. Len);
+ -- Digits of number, most significant first, represented in base
+ -- 2**Base. No leading zeroes are stored, and the value of zero is
+ -- represented using an empty vector for D.
+ end record;
+
+ for Bignum_Data use record
+ Len at 0 range 0 .. 23;
+ Neg at 3 range 0 .. 7;
+ end record;
+
+ type Bignum is access all Bignum_Data;
+ -- This is the type that is used externally. Possibly this could be a
+ -- private type, but we leave the structure exposed for now. For one
+ -- thing it helps with debugging. Note that this package never shares
+ -- an allocated Bignum value, so for example for X + 0, a copy of X is
+ -- returned, not X itself.
+
+ -- Note: none of the subprograms in this package modify the Bignum_Data
+ -- records referenced by Bignum arguments of mode IN.
+
+ function Big_Add (X, Y : Bignum) return Bignum; -- "+"
+ function Big_Sub (X, Y : Bignum) return Bignum; -- "-"
+ function Big_Mul (X, Y : Bignum) return Bignum; -- "*"
+ function Big_Div (X, Y : Bignum) return Bignum; -- "/"
+ function Big_Exp (X, Y : Bignum) return Bignum; -- "**"
+ function Big_Mod (X, Y : Bignum) return Bignum; -- "mod"
+ function Big_Rem (X, Y : Bignum) return Bignum; -- "rem"
+ function Big_Neg (X : Bignum) return Bignum; -- "-"
+ function Big_Abs (X : Bignum) return Bignum; -- "abs"
+ -- Perform indicated arithmetic operation on bignum values. No exception
+ -- raised except for Div/Mod/Rem by 0 which raises Constraint_Error with
+ -- an appropriate message.
+
+ function Big_EQ (X, Y : Bignum) return Boolean; -- "="
+ function Big_NE (X, Y : Bignum) return Boolean; -- "/="
+ function Big_GE (X, Y : Bignum) return Boolean; -- ">="
+ function Big_LE (X, Y : Bignum) return Boolean; -- "<="
+ function Big_GT (X, Y : Bignum) return Boolean; -- ">"
+ function Big_LT (X, Y : Bignum) return Boolean; -- "<"
+ -- Perform indicated comparison on bignums, returning result as Boolean.
+ -- No exception raised for any input arguments.
+
+ function Bignum_In_LLI_Range (X : Bignum) return Boolean;
+ -- Returns True if the Bignum value is in the range of Long_Long_Integer,
+ -- so that a call to From_Bignum is guaranteed not to raise an exception.
+
+ function To_Bignum (X : Long_Long_Integer) return Bignum;
+ -- Convert Long_Long_Integer to Bignum. No exception can be raised for any
+ -- input argument.
+
+ function From_Bignum (X : Bignum) return Long_Long_Integer;
+ -- Convert Bignum to Long_Long_Integer. Constraint_Error raised with
+ -- appropriate message if value is out of range of Long_Long_Integer.
+
+end System.Bignums;