NetBSD 6.1.5 doesn't have ldexpl in math.h

[Gary E. Miller]

Yo Mark!

On Wed, 13 Sep 2017 22:31:31 +0000
Mark Atwood via devel <devel at ntpsec.org> wrote:

> How much complexity would it add to add the missing fp functions in
> the same way the strlcpy function is?

I think all we need for NetBSD 6.1 is ldexpl().

Here is one way, a very slow way, to do it:

long double ldexpl(long double value, int e)
{
  if (value == 0 || value == INFINITY || value == -INFINITY || value != value)
  {
    // Return +0.0/-0.0, +INF/-INF and NaN as-is
  }
  else
  {
    while (e > 0)
      value = value * 2, e--;
    while (e < 0)
      value = value * 0.5f, e++; // won't round denormals correctly
  }
  return value;
}

Ripped from:

https://github.com/alexfru/SmallerC/blob/master/v0100/srclib/ldexp.c

NTPsec only uses 32 and -32 values for 'e', so some simplification
possible.

The INF tests should likely be replaced with isfinite().

RGDS
GARY
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