int ilogb(double x)
{
- union dshape u = {x};
- int e = u.bits>>52 & 0x7ff;
+ #pragma STDC FENV_ACCESS ON
+ union {double f; uint64_t i;} u = {x};
+ uint64_t i = u.i;
+ int e = i>>52 & 0x7ff;
if (!e) {
- u.bits <<= 12;
- if (u.bits == 0)
+ i <<= 12;
+ if (i == 0) {
+ FORCE_EVAL(0/0.0f);
return FP_ILOGB0;
+ }
/* subnormal x */
- // FIXME: scale up subnormals with a *0x1p53 or find top set bit with a better method
- for (e = -0x3ff; u.bits < (uint64_t)1<<63; e--, u.bits<<=1);
+ for (e = -0x3ff; i>>63 == 0; e--, i<<=1);
return e;
}
- if (e == 0x7ff)
- return u.bits<<12 ? FP_ILOGBNAN : INT_MAX;
+ if (e == 0x7ff) {
+ FORCE_EVAL(0/0.0f);
+ return i<<12 ? FP_ILOGBNAN : INT_MAX;
+ }
return e - 0x3ff;
}