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/*
* Written by J.T. Conklin <jtc@netbsd.org>.
* Public domain.
*
* Adapted for `long double' by Ulrich Drepper <drepper@cygnus.com>.
*/
/*
* The 8087 method for the exponential function is to calculate
* exp(x) = 2^(x log2(e))
* after separating integer and fractional parts
* x log2(e) = i + f, |f| <= .5
* 2^i is immediate but f needs to be precise for long double accuracy.
* Suppress range reduction error in computing f by the following.
* Separate x into integer and fractional parts
* x = xi + xf, |xf| <= .5
* Separate log2(e) into the sum of an exact number c0 and small part c1.
* c0 + c1 = log2(e) to extra precision
* Then
* f = (c0 xi - i) + c0 xf + c1 x
* where c0 xi is exact and so also is (c0 xi - i).
* -- moshier@na-net.ornl.gov
*/
#include <math.h>
#include "cephes_mconf.h" /* for max and min log thresholds */
static long double c0 = 1.44268798828125L;
static long double c1 = 7.05260771340735992468e-6L;
static long double
__expl (long double x)
{
long double res;
asm ("fldl2e\n\t" /* 1 log2(e) */
"fmul %%st(1),%%st\n\t" /* 1 x log2(e) */
"frndint\n\t" /* 1 i */
"fld %%st(1)\n\t" /* 2 x */
"frndint\n\t" /* 2 xi */
"fld %%st(1)\n\t" /* 3 i */
"fldt %2\n\t" /* 4 c0 */
"fld %%st(2)\n\t" /* 5 xi */
"fmul %%st(1),%%st\n\t" /* 5 c0 xi */
"fsubp %%st,%%st(2)\n\t" /* 4 f = c0 xi - i */
"fld %%st(4)\n\t" /* 5 x */
"fsub %%st(3),%%st\n\t" /* 5 xf = x - xi */
"fmulp %%st,%%st(1)\n\t" /* 4 c0 xf */
"faddp %%st,%%st(1)\n\t" /* 3 f = f + c0 xf */
"fldt %3\n\t" /* 4 */
"fmul %%st(4),%%st\n\t" /* 4 c1 * x */
"faddp %%st,%%st(1)\n\t" /* 3 f = f + c1 * x */
"f2xm1\n\t" /* 3 2^(fract(x * log2(e))) - 1 */
"fld1\n\t" /* 4 1.0 */
"faddp\n\t" /* 3 2^(fract(x * log2(e))) */
"fstp %%st(1)\n\t" /* 2 */
"fscale\n\t" /* 2 scale factor is st(1); e^x */
"fstp %%st(1)\n\t" /* 1 */
"fstp %%st(1)\n\t" /* 0 */
: "=t" (res) : "0" (x), "m" (c0), "m" (c1) : "ax", "dx");
return res;
}
long double expl (long double x)
{
if (x > MAXLOGL)
return INFINITY;
else if (x < MINLOGL)
return 0.0L;
else
return __expl (x);
}
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