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From: John Maddock (john_at_[hidden])
Date: 2006-10-06 08:59:43

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In reply to: Johan Råde: "[boost] Optimized portable isnan, isfinite, fpclassify etc"
Next in thread: Johan Råde: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"
Reply: Johan Råde: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"
Reply: Johan Råde: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"
Reply: Matt Gruenke: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"

Johan Råde wrote:
> Many of these functions have also been
> implemented by John Maddock.
> The difference is that my implementation
> is optimized for speed.
>
> Here are some timing numbers on VC 7.1:

> The times are in clock cycles for a single call,
> based on an average of 10,000,000 calls
> with random input.

I think the timings for my latest code should be a bit better than that as
I've started forwarding to native versions where applicable.

Even so, I think this is a good idea and worth persuing. Unfortunately I
don't think your code is as portable as you think it is: I'm attaching below
some failed test runs of your code with Intel (Win32 and Linux), HP aCC and
g++ (HP-UX). The difficulty is that once you crank up the optimisation
levels, code like this tends to break, and since it's reason-for-existance
is to improve performance, that's a problem :-(

I have some specific comments on the code:

1) I'm a bit uneasy about the #undef's of the std macros: let's say a user
includes this header indirectly (because it's used by another Boost header,
say my math stuff), they might be a bit miffed if the the macros they were
expecting to be defined have been undef'ed like this.

2) I'm a little surprised at seeing memcpy used to shift 4 bytes, given the
slightly-hairy nature of what you're doing here, I don't think a
reinterpret_cast to uint32 is unreasonable in comparison. But that's just
my opinion :-)

3) With respect to the #error Unknown endianness, perhaps we can forward to
a slower-but safer alternative in this case?

4) I'm fairly sure the declarations:

template<> const boost::uint32_t mask<float>::exponent = 0x7f800000;
template<> const boost::uint32_t mask<double>::exponent = 0x7ff00000;
template<> const boost::uint32_t mask<long double>::exponent

will cause ODR violations / linker errors when the header is used from
multiple TU's.

5) isinf needs to handle the situation where T doesn't have infinities, or
perhaps even doesn't have / can't have numeric_limits support (NTL::RR for
example).

6) Does the implementaton of isnan:

template<class T> bool isnan(T x)
{
return !(x <= std::numeric_limits<T>::infinity());
}

work for negative NaN's ? I'm thinking of compilers that perform
non-standard-IEEE comparisons using faster comparisons of bit-patterns
rather than fully-unordered NaN's.

OK where does this leave us.

Looks like the way forward might be some kind of merger of our
implementations: using the slow-but-safe version as a fallback for where the
fast-and-hairy-version doesn't work?

The difficulty is doing it without the code turning into a spagetty of #if
logic.

I wonder if something like:

template <class T>
T isnan(T x)
{
return isnan_imp(x, typename classify_traits<T>::type());
}

where classify_traits<T>::type is some kind of type that encapsulates:

Endianness.
Is it a real float.
Does it have numeric limits support.
Any compiler specific information - like "use fast if possible", or "always
use safe version".

The we could use compile time dispatch to the right implementation, and all
the hairy logic and #if code would be isolated to classify_traits (or
whatever it's called).

Does this sound plausible, and/or something you might be interested in
persuing?

Thanks,

John.

ps heres the failure logs:

Intel 9.1, Win32, VC-8 mode:

$ icl /O2 /EHs -I../../../develop/boost test.cpp
Intel(R) C++ Compiler for 32-bit applications, Version 9.1 Build
20060519Z
Copyright (C) 1985-2006 Intel Corporation. All rights reserved.
30 DAY EVALUATION LICENSE

-out:test.exe
test.obj

John Maddock_at_fuji /cygdrive/c/data/boost/fpclassify/fpclassify/test
$ ./test
little endian
sizeof(long double) = 8
mask<long double>::exponent = 7ff00000

Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test !isinf(x)
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test !isinf(x)
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test !isinf(x)
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test !isinf(x)
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(x)
Failed test fpclassify(x) == FP_NAN
Failed test isnan(changesign(c))
Failed test isnan(changesign(changesign(c)))
Failed test isnan(changesign(c))
Failed test isnan(changesign(changesign(c)))
Failed test isnan(changesign(c))
Failed test isnan(changesign(changesign(c)))

HP aCC, HP-UX, Itanium:

aCC -AA -O3 -I ~ *.cpp
maddock_at_td176> ./a.out
little endian
sizeof(long double) = 16
mask<long double>::exponent = 0

Failed test fpclassify(x) == FP_ZERO
Failed test signbit(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test signbit(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test signbit(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test !signbit(x)
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test !isfinite(x)
Failed test fpclassify(x) == FP_INFINITE
Failed test signbit(x)
Failed test !isfinite(x)
Failed test fpclassify(x) == FP_INFINITE
Failed test !isfinite(x)
Failed test fpclassify(x) == FP_NAN
Failed test !isfinite(x)
Failed test fpclassify(x) == FP_NAN
Failed test !isfinite(x)
Failed test fpclassify(x) == FP_NAN
Failed test !isfinite(x)
Failed test fpclassify(x) == FP_NAN
Failed test isfinite(x)
Failed test isfinite(x)
Failed test fpclassify(x) == FP_ZERO
Failed test isfinite(x)
Failed test signbit(x)
Failed test isfinite(x)
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test signbit(x)
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test signbit(x)
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test !signbit(x)
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test isfinite(x)
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test fpclassify(x) == FP_INFINITE
Failed test signbit(x)
Failed test fpclassify(x) == FP_INFINITE
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, y) == x
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), y) == x
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test copysign(x, changesign(y)) == changesign(x)
Failed test copysign(changesign(x), changesign(y)) == changesign(x)
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(b) == b
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(a[i]) == -a[i]
Failed test changesign(-a[i]) == a[i]
Failed test !signbit(changesign(-a[i]))
Failed test changesign(b) == b

G++, HP-UX, Itanium:

maddock_at_td176> g++
g++: no input files
maddock_at_td176> g++ -I ~ -O3 *.cpp
maddock_at_td176> ./a.out
little endian
sizeof(long double) = 16
mask<long double>::exponent = 0

Intel 9.1, Linux, Itanium:

maddock_at_[hidden]> icc -I ~ -O3 -fast -fp-model fast=2
*.cpp -stat
ic
IPO: performing single-file optimizations
IPO: generating object file /tmp/ipo_iccbMO6qR.o
maddock_at_[hidden]> ./a.out
little endian
sizeof(long double) = 16
mask<long double>::exponent = 7fff0000

Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test isnormal(x)
Failed test fpclassify(x) == FP_NORMAL
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN
Failed test fpclassify(x) == FP_NAN

Next message: John Maddock: "Re: [boost] [thread] Proposal for thread safe initialization of local static and global objects"
Previous message: Andy Little: "Re: [boost] GIL - Generic Image Library Review - Begins October 5"
In reply to: Johan Råde: "[boost] Optimized portable isnan, isfinite, fpclassify etc"
Next in thread: Johan Råde: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"
Reply: Johan Råde: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"
Reply: Johan Råde: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"
Reply: Matt Gruenke: "Re: [boost] Optimized portable isnan, isfinite, fpclassify etc"

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