/* @(#)s_expm1.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. | |
* ==================================================== | |
*/ | |
#include <LibConfig.h> | |
#include <sys/EfiCdefs.h> | |
#if defined(LIBM_SCCS) && !defined(lint) | |
__RCSID("$NetBSD: s_expm1.c,v 1.12 2002/05/26 22:01:55 wiz Exp $"); | |
#endif | |
#if defined(_MSC_VER) /* Handle Microsoft VC++ compiler specifics. */ | |
// C4756: overflow in constant arithmetic | |
#pragma warning ( disable : 4756 ) | |
#endif | |
/* expm1(x) | |
* Returns exp(x)-1, the exponential of x minus 1. | |
* | |
* Method | |
* 1. Argument reduction: | |
* Given x, find r and integer k such that | |
* | |
* x = k*ln2 + r, |r| <= 0.5*ln2 ~ 0.34658 | |
* | |
* Here a correction term c will be computed to compensate | |
* the error in r when rounded to a floating-point number. | |
* | |
* 2. Approximating expm1(r) by a special rational function on | |
* the interval [0,0.34658]: | |
* Since | |
* r*(exp(r)+1)/(exp(r)-1) = 2+ r^2/6 - r^4/360 + ... | |
* we define R1(r*r) by | |
* r*(exp(r)+1)/(exp(r)-1) = 2+ r^2/6 * R1(r*r) | |
* That is, | |
* R1(r**2) = 6/r *((exp(r)+1)/(exp(r)-1) - 2/r) | |
* = 6/r * ( 1 + 2.0*(1/(exp(r)-1) - 1/r)) | |
* = 1 - r^2/60 + r^4/2520 - r^6/100800 + ... | |
* We use a special Reme algorithm on [0,0.347] to generate | |
* a polynomial of degree 5 in r*r to approximate R1. The | |
* maximum error of this polynomial approximation is bounded | |
* by 2**-61. In other words, | |
* R1(z) ~ 1.0 + Q1*z + Q2*z**2 + Q3*z**3 + Q4*z**4 + Q5*z**5 | |
* where Q1 = -1.6666666666666567384E-2, | |
* Q2 = 3.9682539681370365873E-4, | |
* Q3 = -9.9206344733435987357E-6, | |
* Q4 = 2.5051361420808517002E-7, | |
* Q5 = -6.2843505682382617102E-9; | |
* (where z=r*r, and the values of Q1 to Q5 are listed below) | |
* with error bounded by | |
* | 5 | -61 | |
* | 1.0+Q1*z+...+Q5*z - R1(z) | <= 2 | |
* | | | |
* | |
* expm1(r) = exp(r)-1 is then computed by the following | |
* specific way which minimize the accumulation rounding error: | |
* 2 3 | |
* r r [ 3 - (R1 + R1*r/2) ] | |
* expm1(r) = r + --- + --- * [--------------------] | |
* 2 2 [ 6 - r*(3 - R1*r/2) ] | |
* | |
* To compensate the error in the argument reduction, we use | |
* expm1(r+c) = expm1(r) + c + expm1(r)*c | |
* ~ expm1(r) + c + r*c | |
* Thus c+r*c will be added in as the correction terms for | |
* expm1(r+c). Now rearrange the term to avoid optimization | |
* screw up: | |
* ( 2 2 ) | |
* ({ ( r [ R1 - (3 - R1*r/2) ] ) } r ) | |
* expm1(r+c)~r - ({r*(--- * [--------------------]-c)-c} - --- ) | |
* ({ ( 2 [ 6 - r*(3 - R1*r/2) ] ) } 2 ) | |
* ( ) | |
* | |
* = r - E | |
* 3. Scale back to obtain expm1(x): | |
* From step 1, we have | |
* expm1(x) = either 2^k*[expm1(r)+1] - 1 | |
* = or 2^k*[expm1(r) + (1-2^-k)] | |
* 4. Implementation notes: | |
* (A). To save one multiplication, we scale the coefficient Qi | |
* to Qi*2^i, and replace z by (x^2)/2. | |
* (B). To achieve maximum accuracy, we compute expm1(x) by | |
* (i) if x < -56*ln2, return -1.0, (raise inexact if x!=inf) | |
* (ii) if k=0, return r-E | |
* (iii) if k=-1, return 0.5*(r-E)-0.5 | |
* (iv) if k=1 if r < -0.25, return 2*((r+0.5)- E) | |
* else return 1.0+2.0*(r-E); | |
* (v) if (k<-2||k>56) return 2^k(1-(E-r)) - 1 (or exp(x)-1) | |
* (vi) if k <= 20, return 2^k((1-2^-k)-(E-r)), else | |
* (vii) return 2^k(1-((E+2^-k)-r)) | |
* | |
* Special cases: | |
* expm1(INF) is INF, expm1(NaN) is NaN; | |
* expm1(-INF) is -1, and | |
* for finite argument, only expm1(0)=0 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 expm1(x) overflow | |
* | |
* 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 "math.h" | |
#include "math_private.h" | |
static const double | |
one = 1.0, | |
huge = 1.0e+300, | |
tiny = 1.0e-300, | |
o_threshold = 7.09782712893383973096e+02,/* 0x40862E42, 0xFEFA39EF */ | |
ln2_hi = 6.93147180369123816490e-01,/* 0x3fe62e42, 0xfee00000 */ | |
ln2_lo = 1.90821492927058770002e-10,/* 0x3dea39ef, 0x35793c76 */ | |
invln2 = 1.44269504088896338700e+00,/* 0x3ff71547, 0x652b82fe */ | |
/* scaled coefficients related to expm1 */ | |
Q1 = -3.33333333333331316428e-02, /* BFA11111 111110F4 */ | |
Q2 = 1.58730158725481460165e-03, /* 3F5A01A0 19FE5585 */ | |
Q3 = -7.93650757867487942473e-05, /* BF14CE19 9EAADBB7 */ | |
Q4 = 4.00821782732936239552e-06, /* 3ED0CFCA 86E65239 */ | |
Q5 = -2.01099218183624371326e-07; /* BE8AFDB7 6E09C32D */ | |
double | |
expm1(double x) | |
{ | |
double y,hi,lo,c,t,e,hxs,hfx,r1; | |
int32_t k,xsb; | |
u_int32_t hx; | |
c = 0; | |
GET_HIGH_WORD(hx,x); | |
xsb = hx&0x80000000; /* sign bit of x */ | |
if(xsb==0) y=x; else y= -x; /* y = |x| */ | |
hx &= 0x7fffffff; /* high word of |x| */ | |
/* filter out huge and non-finite argument */ | |
if(hx >= 0x4043687A) { /* if |x|>=56*ln2 */ | |
if(hx >= 0x40862E42) { /* if |x|>=709.78... */ | |
if(hx>=0x7ff00000) { | |
u_int32_t low; | |
GET_LOW_WORD(low,x); | |
if(((hx&0xfffff)|low)!=0) | |
return x+x; /* NaN */ | |
else return (xsb==0)? x:-1.0;/* exp(+-inf)={inf,-1} */ | |
} | |
if(x > o_threshold) return huge*huge; /* overflow */ | |
} | |
if(xsb!=0) { /* x < -56*ln2, return -1.0 with inexact */ | |
if(x+tiny<0.0) /* raise inexact */ | |
return tiny-one; /* return -1 */ | |
} | |
} | |
/* argument reduction */ | |
if(hx > 0x3fd62e42) { /* if |x| > 0.5 ln2 */ | |
if(hx < 0x3FF0A2B2) { /* and |x| < 1.5 ln2 */ | |
if(xsb==0) | |
{hi = x - ln2_hi; lo = ln2_lo; k = 1;} | |
else | |
{hi = x + ln2_hi; lo = -ln2_lo; k = -1;} | |
} else { | |
k = (int32_t)(invln2*x+((xsb==0)?0.5:-0.5)); | |
t = k; | |
hi = x - t*ln2_hi; /* t*ln2_hi is exact here */ | |
lo = t*ln2_lo; | |
} | |
x = hi - lo; | |
c = (hi-x)-lo; | |
} | |
else if(hx < 0x3c900000) { /* when |x|<2**-54, return x */ | |
t = huge+x; /* return x with inexact flags when x!=0 */ | |
return x - (t-(huge+x)); | |
} | |
else k = 0; | |
/* x is now in primary range */ | |
hfx = 0.5*x; | |
hxs = x*hfx; | |
r1 = one+hxs*(Q1+hxs*(Q2+hxs*(Q3+hxs*(Q4+hxs*Q5)))); | |
t = 3.0-r1*hfx; | |
e = hxs*((r1-t)/(6.0 - x*t)); | |
if(k==0) return x - (x*e-hxs); /* c is 0 */ | |
else { | |
e = (x*(e-c)-c); | |
e -= hxs; | |
if(k== -1) return 0.5*(x-e)-0.5; | |
if(k==1) { | |
if(x < -0.25) return -2.0*(e-(x+0.5)); | |
else return one+2.0*(x-e); | |
} | |
if (k <= -2 || k>56) { /* suffice to return exp(x)-1 */ | |
u_int32_t high; | |
y = one-(e-x); | |
GET_HIGH_WORD(high,y); | |
SET_HIGH_WORD(y,high+(k<<20)); /* add k to y's exponent */ | |
return y-one; | |
} | |
t = one; | |
if(k<20) { | |
u_int32_t high; | |
SET_HIGH_WORD(t,0x3ff00000 - (0x200000>>k)); /* t=1-2^-k */ | |
y = t-(e-x); | |
GET_HIGH_WORD(high,y); | |
SET_HIGH_WORD(y,high+(k<<20)); /* add k to y's exponent */ | |
} else { | |
u_int32_t high; | |
SET_HIGH_WORD(t,((0x3ff-k)<<20)); /* 2^-k */ | |
y = x-(e+t); | |
y += one; | |
GET_HIGH_WORD(high,y); | |
SET_HIGH_WORD(y,high+(k<<20)); /* add k to y's exponent */ | |
} | |
} | |
return y; | |
} |