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