third_party/ulib/musl/src/math/logb.c

#include <math.h>

/*
special cases:
        logb(+-0) = -inf, and raise divbyzero
        logb(+-inf) = +inf
        logb(nan) = nan
*/

double logb(double x) {
    if (!isfinite(x))
        return x * x;
    if (x == 0)
        return -1 / (x * x);
    return ilogb(x);
}