156 lines
4.9 KiB
C
156 lines
4.9 KiB
C
/*
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* Copyright (c) 1985 Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms are permitted provided
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* that: (1) source distributions retain this entire copyright notice and
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* comment, and (2) distributions including binaries display the following
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* acknowledgement: ``This product includes software developed by the
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* University of California, Berkeley and its contributors'' in the
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* documentation or other materials provided with the distribution and in
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* all advertising materials mentioning features or use of this software.
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* Neither the name of the University nor the names of its contributors may
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* be used to endorse or promote products derived from this software without
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* specific prior written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*/
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#ifndef lint
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static char sccsid[] = "@(#)asincos.c 5.5 (Berkeley) 10/9/90";
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#endif /* not lint */
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/* ASIN(X)
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* RETURNS ARC SINE OF X
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* DOUBLE PRECISION (IEEE DOUBLE 53 bits, VAX D FORMAT 56 bits)
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* CODED IN C BY K.C. NG, 4/16/85, REVISED ON 6/10/85.
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*
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* Required system supported functions:
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* copysign(x,y)
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* sqrt(x)
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*
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* Required kernel function:
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* atan2(y,x)
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*
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* Method :
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* asin(x) = atan2(x,sqrt(1-x*x)); for better accuracy, 1-x*x is
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* computed as follows
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* 1-x*x if x < 0.5,
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* 2*(1-|x|)-(1-|x|)*(1-|x|) if x >= 0.5.
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*
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* Special cases:
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* if x is NaN, return x itself;
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* if |x|>1, return NaN.
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*
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* Accuracy:
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* 1) If atan2() uses machine PI, then
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*
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* asin(x) returns (PI/pi) * (the exact arc sine of x) nearly rounded;
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* and PI is the exact pi rounded to machine precision (see atan2 for
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* details):
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*
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* in decimal:
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* pi = 3.141592653589793 23846264338327 .....
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* 53 bits PI = 3.141592653589793 115997963 ..... ,
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* 56 bits PI = 3.141592653589793 227020265 ..... ,
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*
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* in hexadecimal:
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* pi = 3.243F6A8885A308D313198A2E....
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* 53 bits PI = 3.243F6A8885A30 = 2 * 1.921FB54442D18 error=.276ulps
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* 56 bits PI = 3.243F6A8885A308 = 4 * .C90FDAA22168C2 error=.206ulps
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*
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* In a test run with more than 200,000 random arguments on a VAX, the
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* maximum observed error in ulps (units in the last place) was
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* 2.06 ulps. (comparing against (PI/pi)*(exact asin(x)));
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*
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* 2) If atan2() uses true pi, then
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*
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* asin(x) returns the exact asin(x) with error below about 2 ulps.
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*
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* In a test run with more than 1,024,000 random arguments on a VAX, the
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* maximum observed error in ulps (units in the last place) was
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* 1.99 ulps.
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*/
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double asin(x)
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double x;
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{
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double s,t,copysign(),atan2(),sqrt(),one=1.0;
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#if !defined(vax)&&!defined(tahoe)
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if(x!=x) return(x); /* x is NaN */
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#endif /* !defined(vax)&&!defined(tahoe) */
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s=copysign(x,one);
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if(s <= 0.5)
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return(atan2(x,sqrt(one-x*x)));
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else
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{ t=one-s; s=t+t; return(atan2(x,sqrt(s-t*t))); }
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}
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/* ACOS(X)
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* RETURNS ARC COS OF X
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* DOUBLE PRECISION (IEEE DOUBLE 53 bits, VAX D FORMAT 56 bits)
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* CODED IN C BY K.C. NG, 4/16/85, REVISED ON 6/10/85.
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*
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* Required system supported functions:
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* copysign(x,y)
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* sqrt(x)
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*
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* Required kernel function:
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* atan2(y,x)
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*
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* Method :
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* ________
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* / 1 - x
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* acos(x) = 2*atan2( / -------- , 1 ) .
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* \/ 1 + x
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*
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* Special cases:
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* if x is NaN, return x itself;
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* if |x|>1, return NaN.
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*
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* Accuracy:
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* 1) If atan2() uses machine PI, then
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*
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* acos(x) returns (PI/pi) * (the exact arc cosine of x) nearly rounded;
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* and PI is the exact pi rounded to machine precision (see atan2 for
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* details):
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*
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* in decimal:
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* pi = 3.141592653589793 23846264338327 .....
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* 53 bits PI = 3.141592653589793 115997963 ..... ,
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* 56 bits PI = 3.141592653589793 227020265 ..... ,
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*
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* in hexadecimal:
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* pi = 3.243F6A8885A308D313198A2E....
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* 53 bits PI = 3.243F6A8885A30 = 2 * 1.921FB54442D18 error=.276ulps
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* 56 bits PI = 3.243F6A8885A308 = 4 * .C90FDAA22168C2 error=.206ulps
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*
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* In a test run with more than 200,000 random arguments on a VAX, the
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* maximum observed error in ulps (units in the last place) was
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* 2.07 ulps. (comparing against (PI/pi)*(exact acos(x)));
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*
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* 2) If atan2() uses true pi, then
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*
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* acos(x) returns the exact acos(x) with error below about 2 ulps.
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*
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* In a test run with more than 1,024,000 random arguments on a VAX, the
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* maximum observed error in ulps (units in the last place) was
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* 2.15 ulps.
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*/
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double acos(x)
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double x;
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{
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double t,copysign(),atan2(),sqrt(),one=1.0;
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#if !defined(vax)&&!defined(tahoe)
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if(x!=x) return(x);
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#endif /* !defined(vax)&&!defined(tahoe) */
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if( x != -1.0)
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t=atan2(sqrt((one-x)/(one+x)),one);
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else
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t=atan2(one,0.0); /* t = PI/2 */
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return(t+t);
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}
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