logbf.c

/*******************************************************************************
MIT License
-----------

Copyright (c) 2002-2019 Advanced Micro Devices, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this Software and associated documentaon files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
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THE SOFTWARE.
*******************************************************************************/

#include "libm.h"
#include "libm_util.h"

#define USE_INFINITYF_WITH_FLAGS
#define USE_HANDLE_ERRORF
#include "libm_inlines.h"
#undef USE_INFINITYF_WITH_FLAGS
#undef USE_HANDLE_ERRORF

#include "libm_errno.h"

float _logbf(float x)
{
  unsigned int ux;
  int u;
  GET_BITS_SP32(x, ux);
  u = ((ux & EXPBITS_SP32) >> EXPSHIFTBITS_SP32) - EXPBIAS_SP32;
  if ((ux & ~SIGNBIT_SP32) == 0)
    /* x is +/-zero. Return -infinity with div-by-zero flag. */
    return _handle_errorf("_logbf", OP_LOGB, NINFBITPATT_SP32, _SING,
                         AMD_F_DIVBYZERO, ERANGE, x, 0.0F, 1);
  else if (EMIN_SP32 <= u && u <= EMAX_SP32)
    /* x is a normal number */
    return (float)u;
  else if (u > EMAX_SP32)
    {
      /* x is infinity or NaN */
      if ((ux & MANTBITS_SP32) == 0)
        /* x is +/-infinity. For VC++, return infinity of same sign. */
        return x;
      else
        /* x is NaN, result is NaN */
        return _handle_errorf("_logbf", OP_LOGB, ux|0x00400000, _DOMAIN,
                             0, EDOM, x, 0.0F, 1);
    }
  else
    {
      /* x is denormalized. */
#ifdef FOLLOW_IEEE754_LOGB
      /* Return the value of the minimum exponent to ensure that
         the relationship between logb and scalb, defined in
         IEEE 754, holds. */
      return EMIN_SP32;
#else
      /* Follow the rule set by IEEE 854 for logb */
      ux &= MANTBITS_SP32;
      u = EMIN_SP32;
      while (ux < IMPBIT_SP32)
        {
          ux <<= 1;
          u--;
        }
      return (float)u;
#endif
    }
}