projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 95f51977 | 1 | /* @(#)log.c 4.2 1/22/85 */ |
| d571f5dd SL |
2 | |
| 3 | /* | |
| 4 | log returns the natural logarithm of its floating | |
| 5 | point argument. | |
| 6 | ||
| 7 | The coefficients are #2705 from Hart & Cheney. (19.38D) | |
| 8 | ||
| 9 | It calls frexp. | |
| 10 | */ | |
| 11 | ||
| 12 | #include <errno.h> | |
| 13 | #include <math.h> | |
| 14 | ||
| 15 | int errno; | |
| 16 | double frexp(); | |
| 17 | static double log2 = 0.693147180559945309e0; | |
| 18 | static double ln10 = 2.302585092994045684; | |
| 19 | static double sqrto2 = 0.707106781186547524e0; | |
| 20 | static double p0 = -.240139179559210510e2; | |
| 21 | static double p1 = 0.309572928215376501e2; | |
| a52057f1 | 22 | static double p2 = -.963769093377840513e1; |
| d571f5dd SL |
23 | static double p3 = 0.421087371217979714e0; |
| 24 | static double q0 = -.120069589779605255e2; | |
| 25 | static double q1 = 0.194809660700889731e2; | |
| 26 | static double q2 = -.891110902798312337e1; | |
| 27 | ||
| 28 | double | |
| 29 | log(arg) | |
| 30 | double arg; | |
| 31 | { | |
| 32 | double x,z, zsq, temp; | |
| 33 | int exp; | |
| 34 | ||
| 35 | if(arg <= 0.) { | |
| 36 | errno = EDOM; | |
| 37 | return(-HUGE); | |
| 38 | } | |
| 39 | x = frexp(arg,&exp); | |
| 40 | while(x<0.5) { | |
| 41 | x = x*2; | |
| 42 | exp = exp-1; | |
| 43 | } | |
| 44 | if(x<sqrto2) { | |
| 45 | x = 2*x; | |
| 46 | exp = exp-1; | |
| 47 | } | |
| 48 | ||
| 49 | z = (x-1)/(x+1); | |
| 50 | zsq = z*z; | |
| 51 | ||
| 52 | temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0; | |
| 53 | temp = temp/(((1.0*zsq + q2)*zsq + q1)*zsq + q0); | |
| 54 | temp = temp*z + exp*log2; | |
| 55 | return(temp); | |
| 56 | } | |
| 57 | ||
| 58 | double | |
| 59 | log10(arg) | |
| 60 | double arg; | |
| 61 | { | |
| 62 | ||
| 63 | return(log(arg)/ln10); | |
| 64 | } |