[GHC] #9534: IEEE Standard 754 for Binary Floating-Point Arithmetic by Prof. W. Kahan, UCB

[GHC]

#9534: IEEE Standard 754 for Binary Floating-Point Arithmetic by Prof. W. Kahan,
UCB
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       Reporter:  jrp                |                   Owner:
           Type:  task               |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Test Suite         |                 Version:  7.8.3
       Keywords:  IEEE754            |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Moderate (less     |         Type of failure:  Incorrect
  than a day)                        |  result at runtime
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
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 The attached is an implementation of the floating point accuracy test
 described in ''The Baleful Influence of Benchmarks'' section of
 http://www.eecs.berkeley.edu/~wkahan/ieee754status/IEEE754.PDF


 {{{
 Results for Float:
 r = 4098.0 produces 12.0 and 12.0 sig. bits
 r = 4098.25 fails: root 0.99989897 isn't at least 1 <<<<
 r = 4097.004 produces 12.0 and 11.999298 sig. bits
 :
 Worst accuracy is 11.999298 sig. bits

 :

 Results for Double:
 r = 4098.0 produces Infinity and Infinity sig. bits
 r = 4098.25 produces Infinity and 53.0 sig. bits
 r = 4097.00390625 produces Infinity and 53.451178091541244 sig. bits
 r = 1.6777218e7 produces Infinity and Infinity sig. bits
 r = 1.677721825e7 produces Infinity and 75.0 sig. bits
 r = 1.6777219e7 produces Infinity and 71.0 sig. bits
 r = 9.4906267e7 produces 26.499999994288153 and 26.499999986733027 sig.
 bits
 r = 9.490626725e7 fails: root 0.999999995635551 isn't at least 1 <<<
 r = 2.684354505e8 produces 28.0 and 27.999999919383132 sig. bits
 r = 2.684354515e8 produces 28.0 and 27.99999993013205 sig. bits
 r = 2.68435458e8 produces 28.0 and 28.0 sig. bits
 r = 2.6843545825e8 produces 28.0 and 28.00000000268723 sig. bits
 r = 2.6843545700000006e8 produces 28.0 and 27.999999989251084 sig. bits
 r = 4.294967298e9 produces 32.0 and 32.0 sig. bits
 r = 4.29496729825e9 produces 32.0 and 32.00000000016795 sig. bits
 Worst accuracy is 26.499999986733027 sig. bits
 }}}

 This seems to be comparable to a clang version, but seems to be fairly
 poor in comparison to some other machines, back in the day (1997).

 '''The attached could, possibly be turned into a testsuite test, by
 removing the QuickCheck tests that are included.'''

 Observations:

 * There are a couple of failures (could be the implementation of sqrt or
 log).
 * signum seems incorrect (signum Nan = -1.0)
 * The prelude should have a copysign function
 * min fails to produce the other argument if one argument is NaN
 * The CFloat and CDouble variants seem to produce the same result as the
 native Float and Double versions
 * The Haskell coding style could be improved to remove some boilerplate,
 make the code more idiomatic
 * There may be a better way of entering the test values of r to ensure
 that they are accurate

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9534>
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