Re: [GHC] #4383: Uncanonical display of Double
#4383: Uncanonical display of Double --+- Reporter: daniel.is.fischer| Owner: Type: bug | Status: closed Priority: high | Milestone: 7.0.2 Component: libraries/base |Version: 6.12.3 Resolution: fixed| Keywords: Double, show Testcase: | Blockedby: Difficulty: | Os: Unknown/Multiple Blocking: | Architecture: Unknown/Multiple Failure: Incorrect result at runtime | --+- Changes (by igloo): * status: merge = closed * resolution: = fixed Comment: Both merged. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4383#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #4383: Uncanonical display of Double
#4383: Uncanonical display of Double
--+-
Reporter: daniel.is.fischer |Owner:
Type: bug| Status: merge
Priority: high |Milestone: 7.0.2
Component: libraries/base | Version: 6.12.3
Keywords: Double, show | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Incorrect result at runtime
--+-
Changes (by simonmar):
* status: patch = merge
Comment:
I pushed all these to HEAD. We want these two in 7.0.2:
{{{
Sun Oct 24 11:29:42 PDT 2010 Daniel Fischer daniel.is.fisc...@web.de
* FIX #4383
Use a better approximation to logBase 10 2 to prevent leading zeros in
floatToDigits.
Sun Oct 24 19:50:41 BST 2010 Daniel Fischer daniel.is.fisc...@web.de
* Fix typo in floatToDigits
The mDn value for powers of 2 = floatDigits x - 1 was typo'ed, leading
to longer than necessary show results in a few cases (e.g. 2.0^852).
Corrected in accordance with Burger and Dybvig's paper.
}}}
and these two should stay in HEAD only:
{{{
Sun Oct 24 20:07:07 BST 2010 Daniel Fischer daniel.is.fisc...@web.de
* Cache for powers of 10
Add a cache for commonly needed powers of 10 to speed up floatToDigits.
Sun Oct 24 19:59:14 BST 2010 Daniel Fischer daniel.is.fisc...@web.de
* Performance enchancement for floatToDigits
Use quot and quotRem instead of div and divMod for dividing positive
Integers since that is a bit faster.
}}}
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4383#comment:5
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Re: [GHC] #4383: Uncanonical display of Double
#4383: Uncanonical display of Double --+- Reporter: daniel.is.fischer |Owner: Type: bug| Status: patch Priority: high |Milestone: 7.0.2 Component: libraries/base | Version: 6.12.3 Keywords: Double, show | Testcase: Blockedby: | Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Incorrect result at runtime --+- Changes (by simonmar): * priority: normal = high * milestone: = 7.0.2 Comment: Thanks Daniel. I presume we want the fixes in the 7.0 branch and the performance improvements in 7.2. Milestoning for 7.0.2 to get the fixes in initially. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4383#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #4383: Uncanonical display of Double
#4383: Uncanonical display of Double --+- Reporter: daniel.is.fischer | Owner: Type: bug| Status: patch Priority: normal | Component: libraries/base Version: 6.12.3 |Keywords: Double, show Testcase: | Blockedby: Os: Unknown/Multiple |Blocking: Architecture: Unknown/Multiple | Failure: Incorrect result at runtime --+- Changes (by daniel.is.fischer): * status: new = patch Comment: 1. fix4383.dpatch fixes the issue, we no longer overestimate the base 10 logarithm 2. There was a typo (b instead of be) in the distance to the next smaller FP number for powers of floatRadix. I thought it ought to be `b^e` and verified it in the paper. This makes numrun012 fail because now `2 ^ 31 :: Float` shows as 2.1474836e9 instead of 2.1474837e9 (and some other show values change too, e.g. `2.0 ^ 852` was 3.0030067315218801e256 is now 3.00300673152188e256). 3. Performance enhancement by using quot/quotRem instead of div/divMod and using the cache of powers of 2 instead of recomputing. 4. Further performance enhancement by adding a cache for powers of 10. 5. All of the above in one patch. 1. and 2. should be applied since they correct errors.[[BR]] The performance enhancement isn't too bad, I think a few more percent could be squeezed out, but it doesn't solve the fundamental problem of the slowness of show for !RealFloat values (cf. http://www.haskell.org/pipermail/haskell-cafe/2009-June/062904.html). I plan to look into it for 7.2, not now. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4383#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #4383: Uncanonical display of Double
#4383: Uncanonical display of Double
--+-
Reporter: daniel.is.fischer | Owner:
Type: bug| Status: new
Priority: normal | Component: libraries/base
Version: 6.12.3 |Keywords: Double, show
Testcase: | Blockedby:
Os: Unknown/Multiple |Blocking:
Architecture: Unknown/Multiple | Failure: Incorrect result at runtime
--+-
Comment(by daniel.is.fischer):
For starters, a better approximation to logBase 10 2 fixes this,
{{{
if b == 2 base == 10 then
-- logBase 10 2 is slightly bigger than 3/10 so
-- the following will err on the low side. Ignoring
-- the fraction will make it err even more.
-- Haskell promises that p-1 = logBase b f p.
-- (p - 1 + e0) * 3 `div` 10
(p - 1 + e0) * 21306 `quot` 70777
*FloatShow let x :: Double; x = 0.5 ^ 1030
*FloatShow floatToDigits 10 x
([8,6,9,1,6,9,4,7,5,9,7,9,4],-310)
*FloatShow showFloat x
8.691694759794e-311
}}}
but I'd rather check the code carefully to see whether something else
might need fixing (and maybe an earlier convergent of logBase 10 2 will
suffice).
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4383#comment:2
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[GHC] #4383: Uncanonical display of Double
#4383: Uncanonical display of Double
--+-
Reporter: daniel.is.fischer | Owner:
Type: bug| Status: new
Priority: normal | Component: libraries/base
Version: 6.12.3 |Keywords: Double, show
Testcase: | Blockedby:
Os: Unknown/Multiple |Blocking:
Architecture: Unknown/Multiple | Failure: Incorrect result at runtime
--+-
{{{
Prelude 0.5 ^ 1030
0.8691694759794e-310
}}}
Should of course be 8.69...e-311, just to have it on record for now.
I'll take a look at the showing code one of the next days.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4383
GHC http://www.haskell.org/ghc/
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Re: [GHC] #4383: Uncanonical display of Double
#4383: Uncanonical display of Double --+- Reporter: daniel.is.fischer | Owner: Type: bug| Status: new Priority: normal | Component: libraries/base Version: 6.12.3 |Keywords: Double, show Testcase: | Blockedby: Os: Unknown/Multiple |Blocking: Architecture: Unknown/Multiple | Failure: Incorrect result at runtime --+- Changes (by augustss): * cc: lenn...@… (added) Comment: That code is pretty impenetrable. :) My guess is that the log estimator doesn't do the right thing for negative exponents. Try (fixup (k0-1)). -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/4383#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
