ref: d0ab3a0dd8f6355b3603d0fb04043a9ae867639b
dir: /libkern/log.c/
/* log returns the natural logarithm of its floating point argument. The coefficients are #2705 from Hart & Cheney. (19.38D) It calls frexp. */ #include <lib9.h> #define log2 0.693147180559945309e0 #define ln10o1 .4342944819032518276511 #define sqrto2 0.707106781186547524e0 #define p0 -.240139179559210510e2 #define p1 0.309572928215376501e2 #define p2 -.963769093377840513e1 #define p3 0.421087371217979714e0 #define q0 -.120069589779605255e2 #define q1 0.194809660700889731e2 #define q2 -.891110902798312337e1 double log(double arg) { double x, z, zsq, temp; int exp; if(arg <= 0) return NaN(); x = frexp(arg, &exp); while(x < 0.5) { x *= 2; exp--; } if(x < sqrto2) { x *= 2; exp--; } z = (x-1) / (x+1); zsq = z*z; temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0; temp = temp/(((zsq + q2)*zsq + q1)*zsq + q0); temp = temp*z + exp*log2; return temp; } double log10(double arg) { if(arg <= 0) return NaN(); return log(arg) * ln10o1; }