+++ /dev/null
-
-/* @(#)e_exp.c 5.1 93/09/24 */
-/*
- * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
- *
- * Developed at SunPro, a Sun Microsystems, Inc. business.
- * Permission to use, copy, modify, and distribute this
- * software is freely granted, provided that this notice
- * is preserved.
- * ====================================================
- */
-
-/* __ieee754_exp(x)
- * Returns the exponential of x.
- *
- * Method
- * 1. Argument reduction:
- * Reduce x to an r so that |r| <= 0.5*ln2 ~ 0.34658.
- * Given x, find r and integer k such that
- *
- * x = k*ln2 + r, |r| <= 0.5*ln2.
- *
- * Here r will be represented as r = hi-lo for better
- * accuracy.
- *
- * 2. Approximation of exp(r) by a special rational function on
- * the interval [0,0.34658]:
- * Write
- * R(r**2) = r*(exp(r)+1)/(exp(r)-1) = 2 + r*r/6 - r**4/360 + ...
- * We use a special Reme algorithm on [0,0.34658] to generate
- * a polynomial of degree 5 to approximate R. The maximum error
- * of this polynomial approximation is bounded by 2**-59. In
- * other words,
- * R(z) ~ 2.0 + P1*z + P2*z**2 + P3*z**3 + P4*z**4 + P5*z**5
- * (where z=r*r, and the values of P1 to P5 are listed below)
- * and
- * | 5 | -59
- * | 2.0+P1*z+...+P5*z - R(z) | <= 2
- * | |
- * The computation of exp(r) thus becomes
- * 2*r
- * exp(r) = 1 + -------
- * R - r
- * r*R1(r)
- * = 1 + r + ----------- (for better accuracy)
- * 2 - R1(r)
- * where
- * 2 4 10
- * R1(r) = r - (P1*r + P2*r + ... + P5*r ).
- *
- * 3. Scale back to obtain exp(x):
- * From step 1, we have
- * exp(x) = 2^k * exp(r)
- *
- * Special cases:
- * exp(INF) is INF, exp(NaN) is NaN;
- * exp(-INF) is 0, and
- * for finite argument, only exp(0)=1 is exact.
- *
- * Accuracy:
- * according to an error analysis, the error is always less than
- * 1 ulp (unit in the last place).
- *
- * Misc. info.
- * For IEEE double
- * if x > 7.09782712893383973096e+02 then exp(x) overflow
- * if x < -7.45133219101941108420e+02 then exp(x) underflow
- *
- * 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.
- */
-
-#include "fdlibm.h"
-
-#ifndef _DOUBLE_IS_32BITS
-
-#ifdef __STDC__
-static const double
-#else
-static double
-#endif
-one = 1.0,
-halF[2] = {0.5,-0.5,},
-huge = 1.0e+300,
-twom1000= 9.33263618503218878990e-302, /* 2**-1000=0x01700000,0*/
-o_threshold= 7.09782712893383973096e+02, /* 0x40862E42, 0xFEFA39EF */
-u_threshold= -7.45133219101941108420e+02, /* 0xc0874910, 0xD52D3051 */
-ln2HI[2] ={ 6.93147180369123816490e-01, /* 0x3fe62e42, 0xfee00000 */
- -6.93147180369123816490e-01,},/* 0xbfe62e42, 0xfee00000 */
-ln2LO[2] ={ 1.90821492927058770002e-10, /* 0x3dea39ef, 0x35793c76 */
- -1.90821492927058770002e-10,},/* 0xbdea39ef, 0x35793c76 */
-invln2 = 1.44269504088896338700e+00, /* 0x3ff71547, 0x652b82fe */
-P1 = 1.66666666666666019037e-01, /* 0x3FC55555, 0x5555553E */
-P2 = -2.77777777770155933842e-03, /* 0xBF66C16C, 0x16BEBD93 */
-P3 = 6.61375632143793436117e-05, /* 0x3F11566A, 0xAF25DE2C */
-P4 = -1.65339022054652515390e-06, /* 0xBEBBBD41, 0xC5D26BF1 */
-P5 = 4.13813679705723846039e-08; /* 0x3E663769, 0x72BEA4D0 */
-
-
-#ifdef __STDC__
- double __ieee754_exp(double x) /* default IEEE double exp */
-#else
- double __ieee754_exp(x) /* default IEEE double exp */
- double x;
-#endif
-{
- double y,hi,lo,c,t;
- int32_t k,xsb;
- uint32_t hx;
-
- GET_HIGH_WORD(hx,x);
- xsb = (hx>>31)&1; /* sign bit of x */
- hx &= 0x7fffffff; /* high word of |x| */
-
- /* filter out non-finite argument */
- if(hx >= 0x40862E42) { /* if |x|>=709.78... */
- if(hx>=0x7ff00000) {
- uint32_t lx;
- GET_LOW_WORD(lx,x);
- if(((hx&0xfffff)|lx)!=0)
- return x+x; /* NaN */
- else return (xsb==0)? x:0.0; /* exp(+-inf)={inf,0} */
- }
- if(x > o_threshold) return huge*huge; /* overflow */
- if(x < u_threshold) return twom1000*twom1000; /* underflow */
- }
-
- /* argument reduction */
- if(hx > 0x3fd62e42) { /* if |x| > 0.5 ln2 */
- if(hx < 0x3FF0A2B2) { /* and |x| < 1.5 ln2 */
- hi = x-ln2HI[xsb]; lo=ln2LO[xsb]; k = 1-xsb-xsb;
- } else {
- k = invln2*x+halF[xsb];
- t = k;
- hi = x - t*ln2HI[0]; /* t*ln2HI is exact here */
- lo = t*ln2LO[0];
- }
- x = hi - lo;
- }
- else if(hx < 0x3e300000) { /* when |x|<2**-28 */
- if(huge+x>one) return one+x;/* trigger inexact */
- }
- else k = 0;
-
- /* x is now in primary range */
- t = x*x;
- c = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
- if(k==0) return one-((x*c)/(c-2.0)-x);
- else y = one-((lo-(x*c)/(2.0-c))-hi);
- if(k >= -1021) {
- uint32_t hy;
- GET_HIGH_WORD(hy,y);
- SET_HIGH_WORD(y,hy+(k<<20)); /* add k to y's exponent */
- return y;
- } else {
- uint32_t hy;
- GET_HIGH_WORD(hy,y);
- SET_HIGH_WORD(y,hy+((k+1000)<<20)); /* add k to y's exponent */
- return y*twom1000;
- }
-}
-
-#endif /* defined(_DOUBLE_IS_32BITS) */
projects / msp430-gcc.git / blobdiff