/* $NetBSD: n_exp__E.c,v 1.7 2008/04/29 15:10:02 uwe Exp $ */
/*
* Copyright (c) 1985, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
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* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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/* exp__E(x,c)
* ASSUMPTION: c << x SO THAT fl(x+c)=x.
* (c is the correction term for x)
* exp__E RETURNS
*
* / exp(x+c) - 1 - x , 1E-19 < |x| < .3465736
* exp__E(x,c) = |
* \ 0 , |x| < 1E-19.
*
* DOUBLE PRECISION (IEEE 53 bits, VAX D FORMAT 56 BITS)
* KERNEL FUNCTION OF EXP, EXPM1, POW FUNCTIONS
* CODED IN C BY K.C. NG, 1/31/85;
* REVISED BY K.C. NG on 3/16/85, 4/16/85.
*
* Required system supported function:
* copysign(x,y)
*
* Method:
* 1. Rational approximation. Let r=x+c.
* Based on
* 2 * sinh(r/2)
* exp(r) - 1 = ---------------------- ,
* cosh(r/2) - sinh(r/2)
* exp__E(r) is computed using
* x*x (x/2)*W - ( Q - ( 2*P + x*P ) )
* --- + (c + x*[---------------------------------- + c ])
* 2 1 - W
* where P := p1*x^2 + p2*x^4,
* Q := q1*x^2 + q2*x^4 (for 56 bits precision, add q3*x^6)
* W := x/2-(Q-x*P),
*
* (See the listing below for the values of p1,p2,q1,q2,q3. The poly-
* nomials P and Q may be regarded as the approximations to sinh
* and cosh :
* sinh(r/2) = r/2 + r * P , cosh(r/2) = 1 + Q . )
*
* The coefficients were obtained by a special Remez algorithm.
*
* Approximation error:
*
* | exp(x) - 1 | 2**(-57), (IEEE double)
* | ------------ - (exp__E(x,0)+x)/x | <=
* | x | 2**(-69). (VAX D)
*
* Constants:
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*/
