Missing RULEs for truncate
I found that the rounding functions from RealFrac class are considerably
slower than the low level functions from GHC.Float. This is really a
problem for me when doing signal processing, since for writing to a common
audio file format or listening to a signal data has to be converted from
Double to Int16.
$ ghci +RTS -M256m -c30 -RTS
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.4.1, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base-1.0 ... linking ... done.
Prelude> :set +s
Prelude> sum $ map round [0.1,0.32..100000] :: Int
1252489463
(6.50 secs, 241894764 bytes)
Prelude> sum $ map floor [0.1,0.32..100000] :: Int
1252262188
(6.07 secs, 240099200 bytes)
Prelude> sum $ map ceiling [0.1,0.32..100000] :: Int
1252716734
(6.13 secs, 243795404 bytes)
Prelude> sum $ map truncate [0.1,0.32..100000] :: Int
1252262188
(6.76 secs, 234572324 bytes)
Prelude> sum $ map GHC.Float.double2Int [0.1,0.32..100000] :: Int
1252262188
(1.38 secs, 66137016 bytes)As far as I can judge, double2Int does the same like truncate. Instead
of using the methods from RealFrac I could simply use double2Int but I
consider this a work-around.
In GHC-6.6.1 these examples end with a stack overflow, but if I shorten the list, the time relations remain the same.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.4.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | libraries/base |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | ghc-bug@henning-thielemann.de |
| Operating system | Linux |
| Architecture | Unknown |