projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 5d130d40 RM |
1 | /* |
| 2 | floating point tangent | |
| 3 | ||
| 4 | A series is used after range reduction. | |
| 5 | Coefficients are #4285 from Hart & Cheney. (19.74D) | |
| 6 | */ | |
| 7 | ||
| 8 | #include <errno.h> | |
| 9 | #include <math.h> | |
| 10 | ||
| 11 | int errno; | |
| 12 | static double invpi = 1.27323954473516268; | |
| 13 | static double p0 = -0.1306820264754825668269611177e+5; | |
| 14 | static double p1 = 0.1055970901714953193602353981e+4; | |
| 15 | static double p2 = -0.1550685653483266376941705728e+2; | |
| 16 | static double p3 = 0.3422554387241003435328470489e-1; | |
| 17 | static double p4 = 0.3386638642677172096076369e-4; | |
| 18 | static double q0 = -0.1663895238947119001851464661e+5; | |
| 19 | static double q1 = 0.4765751362916483698926655581e+4; | |
| 20 | static double q2 = -0.1555033164031709966900124574e+3; | |
| 21 | ||
| 22 | double | |
| 23 | tan(arg) | |
| 24 | double arg; | |
| 25 | { | |
| 26 | double modf(); | |
| 27 | double sign, temp, e, x, xsq; | |
| 28 | int flag, i; | |
| 29 | ||
| 30 | flag = 0; | |
| 31 | sign = 1.; | |
| 32 | if(arg < 0.){ | |
| 33 | arg = -arg; | |
| 34 | sign = -1.; | |
| 35 | } | |
| 36 | arg = arg*invpi; /*overflow?*/ | |
| 37 | x = modf(arg,&e); | |
| 38 | i = e; | |
| 39 | switch(i%4) { | |
| 40 | case 1: | |
| 41 | x = 1. - x; | |
| 42 | flag = 1; | |
| 43 | break; | |
| 44 | ||
| 45 | case 2: | |
| 46 | sign = - sign; | |
| 47 | flag = 1; | |
| 48 | break; | |
| 49 | ||
| 50 | case 3: | |
| 51 | x = 1. - x; | |
| 52 | sign = - sign; | |
| 53 | break; | |
| 54 | ||
| 55 | case 0: | |
| 56 | break; | |
| 57 | } | |
| 58 | ||
| 59 | xsq = x*x; | |
| 60 | temp = ((((p4*xsq+p3)*xsq+p2)*xsq+p1)*xsq+p0)*x; | |
| 61 | temp = temp/(((1.0*xsq+q2)*xsq+q1)*xsq+q0); | |
| 62 | ||
| 63 | if(flag == 1) { | |
| 64 | if(temp == 0.) { | |
| 65 | errno = ERANGE; | |
| 66 | if (sign>0) | |
| 67 | return(HUGE); | |
| 68 | return(-HUGE); | |
| 69 | } | |
| 70 | temp = 1./temp; | |
| 71 | } | |
| 72 | return(sign*temp); | |
| 73 | } |