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ape/libm: implement log2 in libc

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This commit is contained in:
Ori Bernstein 2021-01-30 09:19:57 -08:00
parent 273c4bff7a
commit bb250c4c3b
2 changed files with 27 additions and 16 deletions
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1
sys/include/ape/math.h
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@ -25,6 +25,7 @@ extern double exp(double);
extern double frexp(double, int *); extern double frexp(double, int *);
extern double ldexp(double, int); extern double ldexp(double, int);
extern double log(double); extern double log(double);
extern double log2(double);
extern double log10(double); extern double log10(double);
extern double modf(double, double *); extern double modf(double, double *);
extern double pow(double, double); extern double pow(double, double);

42
sys/src/ape/lib/ap/math/log.c
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@ -10,16 +10,17 @@
#include <math.h> #include <math.h>
#include <errno.h> #include <errno.h>
#define log2 0.693147180559945309e0 #define Log2 0.693147180559945309e0
#define ln10o1 .4342944819032518276511 #define Ln2o1 1.4426950408889634073599
#define sqrto2 0.707106781186547524e0 #define Ln10o1 .4342944819032518276511
#define p0 -.240139179559210510e2 #define Sqrto2 0.707106781186547524e0
#define p1 0.309572928215376501e2 #define P0 -.240139179559210510e2
#define p2 -.963769093377840513e1 #define P1 0.309572928215376501e2
#define p3 0.421087371217979714e0 #define P2 -.963769093377840513e1
#define q0 -.120069589779605255e2 #define P3 0.421087371217979714e0
#define q1 0.194809660700889731e2 #define Q0 -.120069589779605255e2
#define q2 -.891110902798312337e1 #define Q1 0.194809660700889731e2
#define Q2 -.891110902798312337e1
double double
log(double arg) log(double arg)
@ -36,7 +37,7 @@ log(double arg)
x *= 2; x *= 2;
exp--; exp--;
} }
if(x < sqrto2) { if(x < Sqrto2) {
x *= 2; x *= 2;
exp--; exp--;
} }
@ -44,19 +45,28 @@ log(double arg)
z = (x-1) / (x+1); z = (x-1) / (x+1);
zsq = z*z; zsq = z*z;
temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0; temp = ((P3*zsq + P2)*zsq + P1)*zsq + P0;
temp = temp/(((zsq + q2)*zsq + q1)*zsq + q0); temp = temp/(((zsq + Q2)*zsq + Q1)*zsq + Q0);
temp = temp*z + exp*log2; temp = temp*z + exp*Log2;
return temp; return temp;
} }
double double
log10(double arg) log10(double arg)
{ {
if(arg <= 0) { if(arg <= 0) {
errno = (arg==0)? ERANGE : EDOM; errno = (arg==0)? ERANGE : EDOM;
return -HUGE_VAL; return -HUGE_VAL;
} }
return log(arg) * ln10o1; return log(arg) * Ln10o1;
}
double
log2(double arg)
{
if(arg <= 0) {
errno = (arg==0)? ERANGE : EDOM;
return -HUGE_VAL;
}
return log(arg) * Ln2o1;
} }