Re: [boost] [math] floating point classification - testinghelpwanted

From: Paul A Bristow (pbristow_at_[hidden])
Date: 2005-12-02 13:11:39

| -----Original Message-----
| From: boost-bounces_at_[hidden] 
| [mailto:boost-bounces_at_[hidden]] On Behalf Of John Maddock
| Sent: 02 December 2005 17:25
| To: boost_at_[hidden]
| Subject: Re: [boost] [math] floating point classification - 
| testinghelpwanted
| 
| Actually if that's correct then things are a lot better than 
| I feared: the 
| text implies that the type behaves as a real type with 
| 106-bit's in the 
| significand.  It also implies that numeric_limits<>::epsilon 
| must be buggy 
| for that platform.  So I'm more confused than ever :-(

If you want to be confused even further, attached is my inexpert stab at
numeric_limits for NTL quad_float which I think may be the same.

But I have asked the package author for his advice and help on this, but so
far no reply (though there are regular package updates).

I'm not sure that epsilon has a exactly defined value but I concluded

        static quad_float epsilon() throw() { return
        2.4651903288156618919116517665087069677288E-32;}; // 2^(1-106) ==
2^105

was my best guess.

But without confirmation of this, in 'testing' NTL math functions, I cheated
using the number of decimal digits

        quad_float tolpc = to_quad_float("1e-30"); // 31 guaranteed decimal
digits, so percent tolerance is about 1e-29
        BOOST_CHECK_CLOSE(x, one, tolpc);

But I'm ready (anxious even) to have someone agree, or correct me. 

Paul

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Paul A Bristow
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