/* $NetBSD: n_expm1.c,v 1.8 2013/11/24 18:50:58 martin Exp $ */
/*
* Copyright (c) 1985, 1993
* The Regents of the University of California. All rights reserved.
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/* EXPM1(X)
* RETURN THE EXPONENTIAL OF X MINUS ONE
* DOUBLE PRECISION (IEEE 53 BITS, VAX D FORMAT 56 BITS)
* CODED IN C BY K.C. NG, 1/19/85;
* REVISED BY K.C. NG on 2/6/85, 3/7/85, 3/21/85, 4/16/85.
*
* Required system supported functions:
* scalb(x,n)
* copysign(x,y)
* finite(x)
*
* Kernel function:
* exp__E(x,c)
*
* Method:
* 1. Argument Reduction: given the input x, find r and integer k such
* that
* x = k*ln2 + r, |r| <= 0.5*ln2 .
* r will be represented as r := z+c for better accuracy.
*
* 2. Compute EXPM1(r)=exp(r)-1 by
*
* EXPM1(r=z+c) := z + exp__E(z,c)
*
* 3. EXPM1(x) = 2^k * ( EXPM1(r) + 1-2^-k ).
*
* Remarks:
* 1. When k=1 and z < -0.25, we use the following formula for
* better accuracy:
* EXPM1(x) = 2 * ( (z+0.5) + exp__E(z,c) )
* 2. To avoid rounding error in 1-2^-k where k is large, we use
* EXPM1(x) = 2^k * { [z+(exp__E(z,c)-2^-k )] + 1 }
* when k>56.
*
* Special cases:
* EXPM1(INF) is INF, EXPM1(NaN) is NaN;
* EXPM1(-INF)= -1;
* for finite argument, only EXPM1(0)=0 is exact.
*
* Accuracy:
* EXPM1(x) returns the exact (exp(x)-1) nearly rounded. In a test run with
* 1,166,000 random arguments on a VAX, the maximum observed error was
* .872 ulps (units of the last place).
*
* 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.
*/
