Fix clog overflow/underflow (bug 13629)

[Joseph S. Myers]

On Mon, 19 Mar 2012, Carlos O'Donell wrote:

> Is there no way to share the scaling code?

Between different functions: they do different things with the scale 
factor and have different requirements for it (for csqrt it's good to 
start with an even power of 2 as scale factor so the scaling back is 
exact, for example).

Between different floating point types for the same function: it might be 
possible to do some sort of C pseudo-template with macros for these 
functions, but I don't think it would be that readable.  (A 
next-generation libm would likely use automatic generation to build 
functions for all the types from a common source, rather than macros in 
the functions themselves.)

Some other functions will need substantially different scaling for their 
overflow / underflow cases.

-- 
Joseph S. Myers
joseph@codesourcery.com