--  -----------------------------------------------------------------------
--  Title:       single_support_functions
--  Last Mod:    Thu Apr  4 12:29:22 1991
--  Author:      Vincent Broman <broman@nosc.mil>
--   Copyright 1990 Vincent Broman
--     Permission granted to copy, modify, or compile this software for
--   one's own use, provided that this copyright notice is preserved intact.
--     Permission granted to distribute compiled binary copies of this
--   software which are linked in with some other application.
--     Permission granted to distribute other copies of this software,
--   provided that (1) any copy which is not source code, i.e. not in the
--   form in which the software is usually maintained, must be accompanied
--   by a copy of the source code from which it was compiled, and (2) the
--   one distributing it must refrain from imposing on the recipient
--   further restrictions on the distribution of this software.
--   
--  Description: 
--
--	a single-precision-only package of functions
--	supporting an implementation of generic_elementary_functions.
-- 
--  Exceptions:  No checking done.  An accidental overflow could be caused
--		 by an argument way outside the spec domain of a function.
--  -----------------------------------------------------------------------
-- 
with float_types;

use float_types;

package single_support_functions is
   

   function reduced_logdel_2 (y: in single) return single;
-- 
-- return the base-2 logarithm of (1+y)/(1-y),
-- y in the interval [ -3+sqrt(8) .. 3-sqrt(8) ].
-- the coefficients are from a rational (even) 1,1 approximation to
-- log_2( (1+y)/(1-y) )/y  with relative error (omitting roundoff) < 1.91e-8.
-- this delivers high relative accuracy for small y.
-- Note: reduced_logdel_2( 0.0) = 0.0 exactly.
-- 

   function reduced_log_2 (x: in single) return single;
-- 
-- return the base-2 logarithm of x, x in the interval [sqrt(1/2),sqrt(2)].
-- 

   procedure log_2_parts (int_part: out single;
			  frac_part: out single;
			  x: in single);
-- 
-- return the integer and fractional part of the
-- base-2 logarithm of x.
-- int_part is a floating pt integer, and abs( frac_part) <= 1/2.
-- 

   function log_2 (x: in single) return single;
-- 
-- return the base-2 logarithm of x, assuming x > 0.0
-- 
-- the value is exact for x an integer power of 2.
-- 

   function reduced_two_to_the (x: in single) return single;
-- 
-- return 2.0**x for x in the interval [-0.524, 0.524].
-- the coefficients are a Remez-optimized rational(3,2) approximation,
-- with relative error (omitting roundoff) < 1e-8.
-- The interval would be [-1/2, 1/2] but we allow some slop.
-- 
   
   function two_to_the (x: in single) return single;
-- 
-- return 2.0**x, underflowing to zero for very negative x,
-- and overflowing for very positive x.
-- 

   function reduced_sin (x: in single) return single;
-- 
-- return sin x for x in the interval [0,pi/4].
-- the coefficients are a chebychev-economized taylor series for
-- sin((1-x)*pi/8)/((1-x)*pi/8) on [-1,1],
-- with absolute error (omitting roundoff) < 2e-8.
-- this gives high relative accuracy for small x.
-- 

   function reduced_cos (x: in single) return single;
-- 
-- return cos x for x in the interval [0,pi/4].
-- the coefficients are a chebychev-economized taylor series for
-- cos((1-x)*pi/8) on [-1,1],
-- with absolute error (omitting roundoff) < 1.8e-9
-- 

   function reduced_arctan (x: in single) return single;
-- 
-- returns arctan x in radians from [-pi/4,pi/4] for x in [-1,1].
-- coefficents from Abramowitz and Stegun p81, #4.4.49 .
-- relative error < 2e-8.
-- 


end single_support_functions;

-- $Header: s_support_functions_s.a,v 3.24 91/04/04 13:22:41 broman Exp $