Bulat Ziganshin wrote:
Hello Simon,
Tuesday, April 18, 2006, 3:02:20 PM, you wrote:
if that is due to the time of reading .hi files, my alternative Binary
library should help in some future
I'd be suprised if you could improve on GHC's binary library. Using
BinMem (reading/writing directly to memory), GHC's binary library is
about as fast as it gets. I'm sure yours wins when dealing with files,
though.
sorry, Simon, but when i found 10x difference in speed (6mb/s vs 60
mb/s) it was on membufs :) although i can't say that the difference
anyway will be 10 times. for so fast lib the time required to traverse
lists is essential. there are also a lot of other possible problems. i
just asking - whether the time required for reading these (or any
other binary) files is essential for compilation speed?
It's been on my todo list for a while to benchmark the various Binary
libraries, since there's a consensus that we need some kind of Binary
functionality in Haskell'.
I said I'd be surprised if GHC's could be improved on. And indeed, I am
now surprised :-) You do point out some places where it could be
improved. The first thing I would do is replace the IOUArray with a
ForeignPtr now, since that lets you unbox the Ptr without losing garbage
collection of the memory, and retains the ability to re-allocate the
storage. How does your library handle memory allocation, do you have to
explicitly free the memory used for the buffer?
To answer your question, reading interface files isn't a bottleneck in
GHC (although improving its speed is definitely worthwhile).
instance Binary Word16 where
get h = do
w1 <- getWord8 h
w2 <- getWord8 h
return $! ((fromIntegral w1 `shiftL` 8) .|. fromIntegral w2)
>
first possible problem here is what getWord8 is not inlined. second -
using of checked arithmetic (operations on Ints may have additional
checks, unlike operations on Int#)
yes, using uncheckedShiftL would be better.
third - it's better to make all
operations on Int and only then pack all data to Int16 constructor
An Int16 is represented using an Int with sign-extension, so it should
be the same.
I agree that making the format independent of word size would also be
good for a general purpose Binary library, although it wouldn't be
helpful for GHC.
Cheers,
Simon
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