fusl/src/math/ilogbl.c

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

#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
int ilogbl(long double x) {
  return ilogb(x);
}
#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
int ilogbl(long double x) {
  PRAGMA_STDC_FENV_ACCESS_ON
  union ldshape u = {x};
  uint64_t m = u.i.m;
  int e = u.i.se & 0x7fff;

  if (!e) {
    if (m == 0) {
      FORCE_EVAL(0 / 0.0f);
      return FP_ILOGB0;
    }
    /* subnormal x */
    for (e = -0x3fff + 1; m >> 63 == 0; e--, m <<= 1)
      ;
    return e;
  }
  if (e == 0x7fff) {
    FORCE_EVAL(0 / 0.0f);
    return m << 1 ? FP_ILOGBNAN : INT_MAX;
  }
  return e - 0x3fff;
}
#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
int ilogbl(long double x) {
#pragma STDC FENV_ACCESS ON
  union ldshape u = {x};
  int e = u.i.se & 0x7fff;

  if (!e) {
    if (x == 0) {
      FORCE_EVAL(0 / 0.0f);
      return FP_ILOGB0;
    }
    /* subnormal x */
    x *= 0x1p120;
    return ilogbl(x) - 120;
  }
  if (e == 0x7fff) {
    FORCE_EVAL(0 / 0.0f);
    u.i.se = 0;
    return u.f ? FP_ILOGBNAN : INT_MAX;
  }
  return e - 0x3fff;
}
#endif