author | convert-repo |
Tue, 31 Dec 2019 04:28:27 +0000 | |
changeset 3995 | d65488cfad3c |
parent 2380 | 9195eccdcbd9 |
permissions | -rw-r--r-- |
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/* @(#)s_log1p.c 1.3 95/01/18 */ |
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/* |
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* ==================================================== |
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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* |
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* Developed at SunSoft, a Sun Microsystems, Inc. business. |
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* Permission to use, copy, modify, and distribute this |
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* software is freely granted, provided that this notice |
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* is preserved. |
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* ==================================================== |
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*/ |
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|
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/* double log1p(double x) |
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* |
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* Method : |
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* 1. Argument Reduction: find k and f such that |
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* 1+x = 2^k * (1+f), |
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* where sqrt(2)/2 < 1+f < sqrt(2) . |
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* |
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* Note. If k=0, then f=x is exact. However, if k!=0, then f |
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* may not be representable exactly. In that case, a correction |
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* term is need. Let u=1+x rounded. Let c = (1+x)-u, then |
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* log(1+x) - log(u) ~ c/u. Thus, we proceed to compute log(u), |
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* and add back the correction term c/u. |
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* (Note: when x > 2**53, one can simply return log(x)) |
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* |
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* 2. Approximation of log1p(f). |
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* Let s = f/(2+f) ; based on log(1+f) = log(1+s) - log(1-s) |
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* = 2s + 2/3 s**3 + 2/5 s**5 + ....., |
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* = 2s + s*R |
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* We use a special Reme algorithm on [0,0.1716] to generate |
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* a polynomial of degree 14 to approximate R The maximum error |
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* of this polynomial approximation is bounded by 2**-58.45. In |
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* other words, |
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* 2 4 6 8 10 12 14 |
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* R(z) ~ Lp1*s +Lp2*s +Lp3*s +Lp4*s +Lp5*s +Lp6*s +Lp7*s |
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* (the values of Lp1 to Lp7 are listed in the program) |
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* and |
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* | 2 14 | -58.45 |
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* | Lp1*s +...+Lp7*s - R(z) | <= 2 |
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* | | |
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* Note that 2s = f - s*f = f - hfsq + s*hfsq, where hfsq = f*f/2. |
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* In order to guarantee error in log below 1ulp, we compute log |
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* by |
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* log1p(f) = f - (hfsq - s*(hfsq+R)). |
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* |
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* 3. Finally, log1p(x) = k*ln2 + log1p(f). |
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* = k*ln2_hi+(f-(hfsq-(s*(hfsq+R)+k*ln2_lo))) |
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* Here ln2 is split into two floating point number: |
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* ln2_hi + ln2_lo, |
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* where n*ln2_hi is always exact for |n| < 2000. |
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* |
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* Special cases: |
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* log1p(x) is NaN with signal if x < -1 (including -INF) ; |
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* log1p(+INF) is +INF; log1p(-1) is -INF with signal; |
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* log1p(NaN) is that NaN with no signal. |
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* |
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* Accuracy: |
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* according to an error analysis, the error is always less than |
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* 1 ulp (unit in the last place). |
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* |
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* Constants: |
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* The hexadecimal values are the intended ones for the following |
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* constants. The decimal values may be used, provided that the |
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* compiler will convert from decimal to binary accurately enough |
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* to produce the hexadecimal values shown. |
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* |
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* Note: Assuming log() return accurate answer, the following |
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* algorithm can be used to compute log1p(x) to within a few ULP: |
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* |
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* u = 1+x; |
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* if(u==1.0) return x ; else |
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* return log(u)*(x/(u-1.0)); |
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* |
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* See HP-15C Advanced Functions Handbook, p.193. |
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*/ |
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#include "fdlibm.h" |
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|
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#ifdef __STDC__ |
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static const double |
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#else |
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static double |
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#endif |
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ln2_hi = 6.93147180369123816490e-01, /* 3fe62e42 fee00000 */ |
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87 |
ln2_lo = 1.90821492927058770002e-10, /* 3dea39ef 35793c76 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
88 |
two54 = 1.80143985094819840000e+16, /* 43500000 00000000 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
89 |
Lp1 = 6.666666666666735130e-01, /* 3FE55555 55555593 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
90 |
Lp2 = 3.999999999940941908e-01, /* 3FD99999 9997FA04 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
91 |
Lp3 = 2.857142874366239149e-01, /* 3FD24924 94229359 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
92 |
Lp4 = 2.222219843214978396e-01, /* 3FCC71C5 1D8E78AF */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
93 |
Lp5 = 1.818357216161805012e-01, /* 3FC74664 96CB03DE */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
94 |
Lp6 = 1.531383769920937332e-01, /* 3FC39A09 D078C69F */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
95 |
Lp7 = 1.479819860511658591e-01; /* 3FC2F112 DF3E5244 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
96 |
|
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
97 |
static double zero = 0.0; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
98 |
|
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
99 |
#ifdef __STDC__ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
100 |
double log1p(double x) |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
101 |
#else |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
102 |
double log1p(x) |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
103 |
double x; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
104 |
#endif |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
105 |
{ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
106 |
double hfsq,f,c,s,z,R,u; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
107 |
int k,hx,hu,ax; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
108 |
|
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
109 |
hx = __HI(x); /* high word of x */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
110 |
ax = hx&0x7fffffff; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
111 |
|
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
112 |
k = 1; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
113 |
if (hx < 0x3FDA827A) { /* x < 0.41422 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
114 |
if(ax>=0x3ff00000) { /* x <= -1.0 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
115 |
if(x==-1.0) return -two54/zero; /* log1p(-1)=+inf */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
116 |
else return (x-x)/(x-x); /* log1p(x<-1)=NaN */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
117 |
} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
118 |
if(ax<0x3e200000) { /* |x| < 2**-29 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
119 |
if(two54+x>zero /* raise inexact */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
120 |
&&ax<0x3c900000) /* |x| < 2**-54 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
121 |
return x; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
122 |
else |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
123 |
return x - x*x*0.5; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
124 |
} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
125 |
if(hx>0||hx<=((int)0xbfd2bec3)) { |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
126 |
k=0;f=x;hu=1;} /* -0.2929<x<0.41422 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
127 |
} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
128 |
if (hx >= 0x7ff00000) return x+x; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
129 |
if(k!=0) { |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
130 |
if(hx<0x43400000) { |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
131 |
u = 1.0+x; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
132 |
hu = __HI(u); /* high word of u */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
133 |
k = (hu>>20)-1023; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
134 |
c = (k>0)? 1.0-(u-x):x-(u-1.0);/* correction term */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
135 |
c /= u; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
136 |
} else { |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
137 |
u = x; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
138 |
hu = __HI(u); /* high word of u */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
139 |
k = (hu>>20)-1023; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
140 |
c = 0; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
141 |
} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
142 |
hu &= 0x000fffff; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
143 |
if(hu<0x6a09e) { |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
144 |
__HI(u) = hu|0x3ff00000; /* normalize u */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
145 |
} else { |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
146 |
k += 1; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
147 |
__HI(u) = hu|0x3fe00000; /* normalize u/2 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
148 |
hu = (0x00100000-hu)>>2; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
149 |
} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
150 |
f = u-1.0; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
151 |
} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
152 |
hfsq=0.5*f*f; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
153 |
if(hu==0) { /* |f| < 2**-20 */ |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
154 |
if(f==zero) if(k==0) return zero; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
155 |
else {c += k*ln2_lo; return k*ln2_hi+c;} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
156 |
R = hfsq*(1.0-0.66666666666666666*f); |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
157 |
if(k==0) return f-R; else |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
158 |
return k*ln2_hi-((R-(k*ln2_lo+c))-f); |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
159 |
} |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
160 |
s = f/(2.0+f); |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
161 |
z = s*s; |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
162 |
R = z*(Lp1+z*(Lp2+z*(Lp3+z*(Lp4+z*(Lp5+z*(Lp6+z*Lp7)))))); |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
163 |
if(k==0) return f-(hfsq-s*(hfsq+R)); else |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
164 |
return k*ln2_hi-((hfsq-(s*(hfsq+R)+(k*ln2_lo+c)))-f); |
fa7400d022a0
Updated to https://swing.fit.cvut.cz/hg/stx.libjava/rev/31f8b995905e
Jan Vrany <jan.vrany@fit.cvut.cz>
parents:
diff
changeset
|
165 |
} |