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

#include "libm.h"
#include <limits.h>

int ilogbf(float x) {
    PRAGMA_STDC_FENV_ACCESS_ON
    union {
        float f;
        uint32_t i;
    } u = {x};
    uint32_t i = u.i;
    int e = i >> 23 & 0xff;

    if (!e) {
        i <<= 9;
        if (i == 0) {
            FORCE_EVAL(0 / 0.0f);
            return FP_ILOGB0;
        }
        /* subnormal x */
        for (e = -0x7f; i >> 31 == 0; e--, i <<= 1)
            ;
        return e;
    }
    if (e == 0xff) {
        FORCE_EVAL(0 / 0.0f);
        return i << 9 ? FP_ILOGBNAN : INT_MAX;
    }
    return e - 0x7f;
}