1------------------------------------------------------------------------------ 2-- -- 3-- GNAT RUN-TIME COMPONENTS -- 4-- -- 5-- S Y S T E M . E X N _ L L F -- 6-- -- 7-- B o d y -- 8-- -- 9-- Copyright (C) 1992-2012, Free Software Foundation, Inc. -- 10-- -- 11-- GNAT is free software; you can redistribute it and/or modify it under -- 12-- terms of the GNU General Public License as published by the Free Soft- -- 13-- ware Foundation; either version 3, or (at your option) any later ver- -- 14-- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- 15-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- 16-- or FITNESS FOR A PARTICULAR PURPOSE. -- 17-- -- 18-- As a special exception under Section 7 of GPL version 3, you are granted -- 19-- additional permissions described in the GCC Runtime Library Exception, -- 20-- version 3.1, as published by the Free Software Foundation. -- 21-- -- 22-- You should have received a copy of the GNU General Public License and -- 23-- a copy of the GCC Runtime Library Exception along with this program; -- 24-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- 25-- <http://www.gnu.org/licenses/>. -- 26-- -- 27-- GNAT was originally developed by the GNAT team at New York University. -- 28-- Extensive contributions were provided by Ada Core Technologies Inc. -- 29-- -- 30------------------------------------------------------------------------------ 31 32package body System.Exn_LLF is 33 34 ------------------------- 35 -- Exn_Long_Long_Float -- 36 ------------------------- 37 38 function Exn_Long_Long_Float 39 (Left : Long_Long_Float; 40 Right : Integer) return Long_Long_Float 41 is 42 Result : Long_Long_Float := 1.0; 43 Factor : Long_Long_Float := Left; 44 Exp : Integer := Right; 45 46 begin 47 -- We use the standard logarithmic approach, Exp gets shifted right 48 -- testing successive low order bits and Factor is the value of the 49 -- base raised to the next power of 2. If the low order bit or Exp is 50 -- set, multiply the result by this factor. For negative exponents, 51 -- invert result upon return. 52 53 if Exp >= 0 then 54 loop 55 if Exp rem 2 /= 0 then 56 Result := Result * Factor; 57 end if; 58 59 Exp := Exp / 2; 60 exit when Exp = 0; 61 Factor := Factor * Factor; 62 end loop; 63 64 return Result; 65 66 -- Here we have a negative exponent, and we compute the result as: 67 68 -- 1.0 / (Left ** (-Right)) 69 70 -- Note that the case of Left being zero is not special, it will 71 -- simply result in a division by zero at the end, yielding a 72 -- correctly signed infinity, or possibly generating an overflow. 73 74 -- Note on overflow: The coding of this routine assumes that the 75 -- target generates infinities with standard IEEE semantics. If this 76 -- is not the case, then the code below may raise Constraint_Error. 77 -- This follows the implementation permission given in RM 4.5.6(12). 78 79 else 80 begin 81 loop 82 if Exp rem 2 /= 0 then 83 Result := Result * Factor; 84 end if; 85 86 Exp := Exp / 2; 87 exit when Exp = 0; 88 Factor := Factor * Factor; 89 end loop; 90 91 return 1.0 / Result; 92 end; 93 end if; 94 end Exn_Long_Long_Float; 95 96end System.Exn_LLF; 97