183 lines
6.1 KiB
Ada
183 lines
6.1 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT RUN-TIME COMPONENTS --
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-- --
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-- S Y S T E M . A R I T H _ 3 2 --
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-- --
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-- B o d y --
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-- --
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-- Copyright (C) 2020, 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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with Ada.Unchecked_Conversion;
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package body System.Arith_32 is
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pragma Suppress (Overflow_Check);
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pragma Suppress (Range_Check);
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subtype Uns32 is Interfaces.Unsigned_32;
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subtype Uns64 is Interfaces.Unsigned_64;
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use Interfaces;
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function To_Int is new Ada.Unchecked_Conversion (Uns32, Int32);
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-----------------------
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-- Local Subprograms --
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-----------------------
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function "abs" (X : Int32) return Uns32 is
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(if X = Int32'First
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then 2**31
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else Uns32 (Int32'(abs X)));
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-- Convert absolute value of X to unsigned. Note that we can't just use
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-- the expression of the Else since it overflows for X = Int32'First.
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function Hi (A : Uns64) return Uns32 is (Uns32 (Shift_Right (A, 32)));
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-- High order half of 64-bit value
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function To_Neg_Int (A : Uns32) return Int32;
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-- Convert to negative integer equivalent. If the input is in the range
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-- 0 .. 2**31, then the corresponding nonpositive signed integer (obtained
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-- by negating the given value) is returned, otherwise constraint error is
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-- raised.
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function To_Pos_Int (A : Uns32) return Int32;
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-- Convert to positive integer equivalent. If the input is in the range
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-- 0 .. 2**31 - 1, then the corresponding nonnegative signed integer is
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-- returned, otherwise constraint error is raised.
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procedure Raise_Error;
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pragma No_Return (Raise_Error);
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-- Raise constraint error with appropriate message
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-----------------
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-- Raise_Error --
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-----------------
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procedure Raise_Error is
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begin
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raise Constraint_Error with "32-bit arithmetic overflow";
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end Raise_Error;
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-------------------
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-- Scaled_Divide --
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-------------------
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procedure Scaled_Divide32
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(X, Y, Z : Int32;
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Q, R : out Int32;
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Round : Boolean)
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is
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Xu : constant Uns32 := abs X;
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Yu : constant Uns32 := abs Y;
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Zu : constant Uns32 := abs Z;
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D : Uns64;
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-- The dividend
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Qu : Uns32;
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Ru : Uns32;
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-- Unsigned quotient and remainder
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begin
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-- First do the 64-bit multiplication
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D := Uns64 (Xu) * Uns64 (Yu);
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-- If dividend is too large, raise error
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if Hi (D) >= Zu then
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Raise_Error;
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-- Then do the 64-bit division
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else
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Qu := Uns32 (D / Uns64 (Zu));
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Ru := Uns32 (D rem Uns64 (Zu));
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end if;
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-- Deal with rounding case
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if Round and then Ru > (Zu - Uns32'(1)) / Uns32'(2) then
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-- Protect against wrapping around when rounding, by signaling
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-- an overflow when the quotient is too large.
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if Qu = Uns32'Last then
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Raise_Error;
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end if;
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Qu := Qu + Uns32'(1);
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end if;
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-- Set final signs (RM 4.5.5(27-30))
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-- Case of dividend (X * Y) sign positive
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if (X >= 0 and then Y >= 0) or else (X < 0 and then Y < 0) then
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R := To_Pos_Int (Ru);
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Q := (if Z > 0 then To_Pos_Int (Qu) else To_Neg_Int (Qu));
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-- Case of dividend (X * Y) sign negative
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else
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R := To_Neg_Int (Ru);
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Q := (if Z > 0 then To_Neg_Int (Qu) else To_Pos_Int (Qu));
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end if;
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end Scaled_Divide32;
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----------------
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-- To_Neg_Int --
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----------------
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function To_Neg_Int (A : Uns32) return Int32 is
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R : constant Int32 :=
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(if A = 2**31 then Int32'First else -To_Int (A));
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-- Note that we can't just use the expression of the Else, because it
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-- overflows for A = 2**31.
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begin
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if R <= 0 then
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return R;
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else
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Raise_Error;
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end if;
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end To_Neg_Int;
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----------------
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-- To_Pos_Int --
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----------------
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function To_Pos_Int (A : Uns32) return Int32 is
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R : constant Int32 := To_Int (A);
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begin
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if R >= 0 then
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return R;
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else
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Raise_Error;
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end if;
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end To_Pos_Int;
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end System.Arith_32;
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