From: Stephen Leake <Stephe.Leake@nasa.gov>
Subject: Re: Epsilon
Date: Tue, 13 May 2008 07:42:35 -0400
Date: 2008-05-13T07:42:35-04:00 [thread overview]
Message-ID: <umymuph04.fsf@nasa.gov> (raw)
In-Reply-To: CRYVj.2543$ah4.2038@flpi148.ffdc.sbc.com
<adaworks@sbcglobal.net> writes:
> I am looking for some short, practical examples of the Epsilon
> attribute. If you do have some source code examples to post,
> please also send them to my academic email: rdriehle@nps.edu
-- These values guarantee Integer_16 (value) or Unsigned_16
-- (value) won't raise Constraint_Error, and allow for maximum
-- round-off error. Useful with Clip_Scale_Limit when result will
-- be converted to Integer_16 or Unsigned_16.
Integer_16_First_Real : constant Real_Type := Real_Type (Interfaces.Integer_16'First) - 0.5 +
(Real_Type'Epsilon * Real_Type (Interfaces.Integer_16'Last));
Integer_16_Last_Real : constant Real_Type := Real_Type (Interfaces.Integer_16'Last) + 0.5 -
(Real_Type'Epsilon * Real_Type (Interfaces.Integer_16'Last));
Unsigned_16_First_Real : constant Real_Type := -0.5 + Real_Type'Epsilon;
Unsigned_16_Last_Real : constant Real_Type := Real_Type (Interfaces.Unsigned_16'Last) + 0.5 -
(Real_Type'Epsilon * Real_Type (Interfaces.Unsigned_16'Last));
function First_Order_Trig return Real_Type
is begin
return Elementary.Sqrt (Real_Type'Model_Epsilon);
end First_Order_Trig;
function Half_Trig (Trig : in Trig_Pair_Type) return Trig_Pair_Type
is
-- The result Trig.Cos is >= 0.0.
--
-- A linear approximation is used when Trig.Sin <
-- First_Order_Trig. this is exact since cos x = 1 - x**2 for
-- this range of x.
begin
if abs Trig.Sin < First_Order_Trig then
-- angle near 0 or Pi.
if Trig.Cos > 0.0 then
-- angle near 0
return (Trig.Sin / 2.0, 1.0);
else -- angle near Pi
if Trig.Sin >= 0.0 then
return (1.0 - Trig.Sin / 2.0, 0.0);
else
return (-1.0 + Trig.Sin / 2.0, 0.0);
end if;
end if;
else -- angle not near 0 or Pi
if Trig.Sin >= 0.0 then
return (Elementary.Sqrt ((1.0 - Trig.Cos) / 2.0), Elementary.Sqrt ((1.0 + Trig.Cos) / 2.0));
else
return (-Elementary.Sqrt ((1.0 - Trig.Cos) / 2.0), Elementary.Sqrt ((1.0 + Trig.Cos) / 2.0));
end if;
end if;
end Half_Trig;
--
-- Stephe
next prev parent reply other threads:[~2008-05-13 11:42 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-05-12 14:56 Epsilon adaworks
2008-05-13 11:42 ` Stephen Leake [this message]
2008-05-14 1:02 ` Epsilon adaworks
2008-05-14 9:58 ` Epsilon Stephen Leake
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