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PDP-10 Archives
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SRI_NIC_PERM_FS_1_19910112
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kcc-6/lib/math/asin.c
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/*
* +++ NAME +++
*
* ASIN Double precision arc sine
*
* +++ INDEX +++
*
* ASIN
* machine independent routines
* trigonometric functions
* math libraries
*
* +++ DESCRIPTION +++
*
* Returns double precision arc sine of double precision
* floating point argument.
*
* +++ USAGE +++
*
* double asin(x)
* double x;
*
* +++ REFERENCES +++
*
* Fortran IV-plus user's guide, Digital Equipment Corp. pp B-2.
*
* +++ RESTRICTIONS +++
*
* For precision information refer to documentation of the floating
* point library primatives called.
*
* +++ PROGRAMMER +++
*
* Fred Fish
* Goodyear Aerospace Corp, Arizona Div.
* (602) 932-7000 work
* (602) 894-6881 home
*
* Modifications for inclusion in standard C library are
* (c) Copyright Ian Macky, SRI International 1985
* Additional modifications after v.3, 2-Jul-1986 are
* (c) Copyright Ken Harrenstien 1989
*
* This routine now conforms with the description of the asin()
* function as defined in
* Harbison & Steele's "C: A Reference Manual", section 11.3.3
*
* +++ INTERNALS +++
*
* Computes arcsine(X) from:
*
* (1) If X = 0.0 then asin(X) = 0.0
*
* (2) If X = 1.0 then asin(X) = PI/2.
*
* (3) If X = -1.0 then asin(X) = -PI/2
*
* (4) If -1.0 < X < 1.0 then
* asin(X) = atan(Y)
* Y = X / sqrt[1-(X**2)]
*
* ---
*/
#include <math.h>
#include <errno.h>
#include "pml.h"
double asin(x)
double x;
{
if (x > 1.0 || x < -1.0) {
errno = EDOM;
return 0.0;
}
if (x == 0.0)
return 0.0;
if (x == 1.0)
return HALFPI;
if (x == -1.0)
return -HALFPI;
return atan(x / sqrt(1.0 - x * x));
}