projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 9cc59523 | 1 | /* |
| be6e3ddf RE |
2 | * Copyright (c) 1980 Regents of the University of California. |
| 3 | * All rights reserved. The Berkeley software License Agreement | |
| 4 | * specifies the terms and conditions for redistribution. | |
| 5 | * | |
| 4d98b990 | 6 | * @(#)r_tan.c 5.3 %G% |
| 9cc59523 DW |
7 | */ |
| 8 | ||
| 4d98b990 | 9 | #ifndef tahoe |
| 46452188 | 10 | float r_tan(x) |
| 9cc59523 DW |
11 | float *x; |
| 12 | { | |
| 13 | double tan(); | |
| 14 | return( tan(*x) ); | |
| 15 | } | |
| 4d98b990 KM |
16 | |
| 17 | #else tahoe | |
| 18 | ||
| 19 | /* | |
| 20 | SINGLE PRECISION floating point tangent | |
| 21 | ||
| 22 | sin/cos is used after argument reduction to [0,pi/4] range. | |
| 23 | since x is in this range, tan(x) is in [0,1] range and | |
| 24 | no overflow can occur here. | |
| 25 | */ | |
| 26 | ||
| 27 | #include <errno.h> | |
| 28 | ||
| 29 | int errno; | |
| 30 | static double invpi = 1.27323954473516268; /* 4/pi */ | |
| 31 | ||
| 32 | float | |
| 33 | r_tan(parg) | |
| 34 | float *parg; | |
| 35 | { | |
| 36 | double arg; | |
| 37 | fortran float sin(), cos(); | |
| 38 | double modf(); | |
| 39 | float flmax_(); | |
| 40 | double temp, e, x, xsq; | |
| 41 | int sign; | |
| 42 | int flag, i; | |
| 43 | ||
| 44 | arg = *parg; | |
| 45 | flag = 0; | |
| 46 | sign = 1.; | |
| 47 | if(arg < 0.){ /* tan(-arg) = -tan(arg) */ | |
| 48 | arg = -arg; | |
| 49 | sign = -1.; | |
| 50 | } | |
| 51 | arg = arg*invpi; /*overflow?*/ | |
| 52 | x = modf(arg,&e); | |
| 53 | i = e; | |
| 54 | switch(i%4) { | |
| 55 | case 1: /* 2nd octant: tan(x) = 1/tan(1-x) */ | |
| 56 | x = 1. - x; | |
| 57 | flag = 1; | |
| 58 | break; | |
| 59 | ||
| 60 | case 2: /* 3rd octant: tan(x) = -1/tan(x) */ | |
| 61 | sign = - sign; | |
| 62 | flag = 1; | |
| 63 | break; | |
| 64 | ||
| 65 | case 3: /* 4th octant: tan(x) = -tan(1-x) */ | |
| 66 | x = 1. - x; | |
| 67 | sign = - sign; | |
| 68 | break; | |
| 69 | ||
| 70 | case 0: /* 1st octant */ | |
| 71 | break; | |
| 72 | } | |
| 73 | x = x/invpi; | |
| 74 | ||
| 75 | temp = sin(x)/cos(x); | |
| 76 | ||
| 77 | if(flag == 1) { | |
| 78 | if(temp == 0.) { /* check for singular "point" */ | |
| 79 | errno = ERANGE; | |
| 80 | if (sign>0) | |
| 81 | return(flmax_()); | |
| 82 | return(-flmax_()); | |
| 83 | } | |
| 84 | temp = 1./temp; | |
| 85 | } | |
| 86 | return(sign*temp); | |
| 87 | } | |
| 88 | ||
| 89 | #endif tahoe |