BSD 4_3_Tahoe release

[unix-history] / usr / src / usr.lib / libF77 / r_tan.c

diff --git a/usr/src/usr.lib/libF77/r_tan.c b/usr/src/usr.lib/libF77/r_tan.c
index c996cb6..7a99d7c 100644 (file)
--- a/usr/src/usr.lib/libF77/r_tan.c
+++ b/usr/src/usr.lib/libF77/r_tan.c
@@ -3,12 +3,87 @@
  * All rights reserved.  The Berkeley software License Agreement
  * specifies the terms and conditions for redistribution.
  *
  * All rights reserved.  The Berkeley software License Agreement
  * specifies the terms and conditions for redistribution.
  *

- *     @(#)r_tan.c     5.2     7/8/85
+ *     @(#)r_tan.c     5.3     11/3/86

  */
 
  */
 

+#ifndef tahoe

 float r_tan(x)
 float *x;
 {
 double tan();
 return( tan(*x) );
 }
 float r_tan(x)
 float *x;
 {
 double tan();
 return( tan(*x) );
 }

+
+#else tahoe
+
+/*
+       SINGLE PRECISION floating point tangent
+
+       sin/cos is used after argument reduction to [0,pi/4] range.
+       since x is in this range, tan(x) is in [0,1] range and
+       no overflow can occur here.
+*/
+
+#include <errno.h>
+
+int    errno;
+static double invpi = 1.27323954473516268;  /* 4/pi */
+
+float
+r_tan(parg)
+float *parg;
+{
+       double arg;
+       fortran float sin(), cos();
+       double modf();
+       float flmax_();
+       double temp, e, x, xsq;
+       int sign;
+       int flag, i;
+
+       arg = *parg;
+       flag = 0;
+       sign = 1.;
+       if(arg < 0.){           /* tan(-arg) = -tan(arg) */
+               arg = -arg;
+               sign = -1.;
+       }
+       arg = arg*invpi;   /*overflow?*/
+       x = modf(arg,&e);
+       i = e;
+       switch(i%4) {
+       case 1:                 /* 2nd octant: tan(x) = 1/tan(1-x) */
+               x = 1. - x;
+               flag = 1;
+               break;
+
+       case 2:                 /* 3rd octant: tan(x) = -1/tan(x) */
+               sign = - sign;
+               flag = 1;
+               break;
+
+       case 3:                 /* 4th octant: tan(x) = -tan(1-x) */
+               x = 1. - x;
+               sign = - sign;
+               break;
+
+       case 0:                 /* 1st octant */
+               break;
+       }
+       x = x/invpi;
+
+       temp = sin(x)/cos(x);
+
+       if(flag == 1) {
+               if(temp == 0.) {        /* check for singular "point" */
+                       errno = ERANGE;
+                       if (sign>0)
+                               return(flmax_());
+                       return(-flmax_());
+               }
+               temp = 1./temp;
+       }
+       return(sign*temp);
+}
+
+#endif tahoe