Use of C99 extra long double math functions after r236148

[Steve Kargl]

On Fri, Jul 20, 2012 at 07:39:44AM +1000, Peter Jeremy wrote:
> On 2012-Jul-18 14:01:42 +1000, Bruce Evans <brde at optusnet.com.au> wrote:
> 
> >The standard classification macros are good for developing things, but
> >they are very slow.  All (?) committed complex functions use hard-coded
> >bit test.
> 
> I notice that the functions are full of hard-coded magic constants.
> Would these be better as macros to:
> 1) Provide a description as to their purpose; and
> 2) Reduce differences between the float/long/double function bodies?
> 

I collected some of the float and double into a cheat sheet.

Idioms used in libm with float type:

  int32_t xsb;
  u_int32_t hx;

  GET_FLOAT_WORD(hx, x);

  /* Get the sign bit of x */
  xsb = (hx >> 31) & 1;

  /* high word of |x| */
  hx &= 0x7fffffff;

  /* NaN */
  if (hx > 0x7f800000)
     return (x + x);

  /* exp(+-inf) = {inf, 0} */
  if (hx == 0x7f800000)
     return (xsb == 0) ? x : 0.0;

  /* subnormal */
  if (hx < 0x00800000)


Idioms used in lib with double type:

  u_int32_t hx, lx, xsb

  EXTRACT_WORDS(hx, lx, x);

  /* sign bit of x */
  xsb = (hx >> 31) & 1;

  /* high word of |x| */
  hx &= 0x7fffffff;

  /* subnormal */
  if (hx < 0x00100000)

  /* Test for NaN and +-Inf. */
  if (hx >= 0x7ff00000) {
     /* Is it a NaN? */
     if (((hx & 0xfffff) | lx) != 0)
        return (x + x);
     /* It's an +-Inf. */
     return ((xsb == 0) ? x : 0.0);    /* exp(+-inf)={inf,0} */
  }


-- 
Steve