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Diffstat (limited to 'gcc/ada/s-expgen.adb')
| -rw-r--r-- | gcc/ada/s-expgen.adb | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/gcc/ada/s-expgen.adb b/gcc/ada/s-expgen.adb new file mode 100644 index 00000000000..4ae3c9830c6 --- /dev/null +++ b/gcc/ada/s-expgen.adb @@ -0,0 +1,183 @@ +------------------------------------------------------------------------------ +-- -- +-- GNAT RUNTIME COMPONENTS -- +-- -- +-- S Y S T E M . E X P _ G E N -- +-- -- +-- B o d y -- +-- -- +-- $Revision: 1.11 $ +-- -- +-- Copyright (C) 1992-2001, 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 2, 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. See the GNU General Public License -- +-- for more details. You should have received a copy of the GNU General -- +-- Public License distributed with GNAT; see file COPYING. If not, write -- +-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- +-- MA 02111-1307, USA. -- +-- -- +-- As a special exception, if other files instantiate generics from this -- +-- unit, or you link this unit with other files to produce an executable, -- +-- this unit does not by itself cause the resulting executable to be -- +-- covered by the GNU General Public License. This exception does not -- +-- however invalidate any other reasons why the executable file might be -- +-- covered by the GNU Public License. -- +-- -- +-- GNAT was originally developed by the GNAT team at New York University. -- +-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). -- +-- -- +------------------------------------------------------------------------------ + +package body System.Exp_Gen is + + -------------------- + -- Exp_Float_Type -- + -------------------- + + function Exp_Float_Type + (Left : Type_Of_Base; + Right : Integer) + return Type_Of_Base + is + Result : Type_Of_Base := 1.0; + Factor : Type_Of_Base := Left; + Exp : Integer := Right; + + begin + -- We use the standard logarithmic approach, Exp gets shifted right + -- testing successive low order bits and Factor is the value of the + -- base raised to the next power of 2. For positive exponents we + -- multiply the result by this factor, for negative exponents, we + -- divide by this factor. + + if Exp >= 0 then + + -- For a positive exponent, if we get a constraint error during + -- this loop, it is an overflow, and the constraint error will + -- simply be passed on to the caller. + + loop + if Exp rem 2 /= 0 then + declare + pragma Unsuppress (All_Checks); + begin + Result := Result * Factor; + end; + end if; + + Exp := Exp / 2; + exit when Exp = 0; + + declare + pragma Unsuppress (All_Checks); + begin + Factor := Factor * Factor; + end; + end loop; + + return Result; + + -- Now we know that the exponent is negative, check for case of + -- base of 0.0 which always generates a constraint error. + + elsif Factor = 0.0 then + raise Constraint_Error; + + -- Here we have a negative exponent with a non-zero base + + else + + -- For the negative exponent case, a constraint error during this + -- calculation happens if Factor gets too large, and the proper + -- response is to return 0.0, since what we essenmtially have is + -- 1.0 / infinity, and the closest model number will be zero. + + begin + loop + if Exp rem 2 /= 0 then + declare + pragma Unsuppress (All_Checks); + begin + Result := Result * Factor; + end; + end if; + + Exp := Exp / 2; + exit when Exp = 0; + + declare + pragma Unsuppress (All_Checks); + begin + Factor := Factor * Factor; + end; + end loop; + + declare + pragma Unsuppress (All_Checks); + begin + return 1.0 / Result; + end; + + exception + + when Constraint_Error => + return 0.0; + end; + end if; + end Exp_Float_Type; + + ---------------------- + -- Exp_Integer_Type -- + ---------------------- + + -- Note that negative exponents get a constraint error because the + -- subtype of the Right argument (the exponent) is Natural. + + function Exp_Integer_Type + (Left : Type_Of_Base; + Right : Natural) + return Type_Of_Base + is + Result : Type_Of_Base := 1; + Factor : Type_Of_Base := Left; + Exp : Natural := Right; + + begin + -- We use the standard logarithmic approach, Exp gets shifted right + -- testing successive low order bits and Factor is the value of the + -- base raised to the next power of 2. + + -- Note: it is not worth special casing the cases of base values -1,0,+1 + -- since the expander does this when the base is a literal, and other + -- cases will be extremely rare. + + if Exp /= 0 then + loop + if Exp rem 2 /= 0 then + declare + pragma Unsuppress (All_Checks); + begin + Result := Result * Factor; + end; + end if; + + Exp := Exp / 2; + exit when Exp = 0; + + declare + pragma Unsuppress (All_Checks); + begin + Factor := Factor * Factor; + end; + end loop; + end if; + + return Result; + end Exp_Integer_Type; + +end System.Exp_Gen; |