1#include "libm.h"
2#include <limits.h>
3
4int ilogb(double x) {
5    PRAGMA_STDC_FENV_ACCESS_ON
6    union {
7        double f;
8        uint64_t i;
9    } u = {x};
10    uint64_t i = u.i;
11    int e = i >> 52 & 0x7ff;
12
13    if (!e) {
14        i <<= 12;
15        if (i == 0) {
16            FORCE_EVAL(0 / 0.0f);
17            return FP_ILOGB0;
18        }
19        /* subnormal x */
20        for (e = -0x3ff; i >> 63 == 0; e--, i <<= 1)
21            ;
22        return e;
23    }
24    if (e == 0x7ff) {
25        FORCE_EVAL(0 / 0.0f);
26        return i << 12 ? FP_ILOGBNAN : INT_MAX;
27    }
28    return e - 0x3ff;
29}
30