On 13/01/14 21:49, Herbert Valerio Riedel wrote:
On 2014-01-13 at 21:57:03 +0100, Simon Marlow wrote:
On 13/01/14 13:25, [email protected] wrote:
Repository : ssh://[email protected]/integer-gmp
On branch : master
Link :
http://ghc.haskell.org/trac/ghc/changeset/7bdcadda7e884edffb1427f0685493f3a2e5c5fa/integer-gmp
---------------------------------------------------------------
commit 7bdcadda7e884edffb1427f0685493f3a2e5c5fa
Author: Herbert Valerio Riedel <[email protected]>
Date: Thu Jan 9 00:19:31 2014 +0100
Allocate initial 1-limb mpz_t on the Stack and introduce MPZ# type
We now allocate a 1-limb mpz_t on the stack instead of doing a more
expensive heap-allocation (especially if the heap-allocated copy becomes
garbage right away); this addresses #8647.
While this is quite cool (turning some J# back into S#), I don't
understand why you've done it this way. Couldn't it be done in the
Haskell layer rather than modifying the primops? The ByteArray# has
already been allocated by GMP, so you don't lose anything by returning
it to Haskell and checking the size there. Then all the
DUMMY_BYTEARRAY stuff would go away.
Actually there isn't always a ByteArray# allocated; the patch got rid of
all mpz_init() calls for the result-mpz_t (which would have allocated
1-limb ByteArray#s);
Now instead, the single word-sized limb that would have been
heap-allocated via mpz_init() before calling the actual GMP operation,
is allocated on the stack instead, and only if the GMP routines need to
grow the passed in mpz_t's an actual ByteArray# is allocated.
That's why I needed a way to return either a single stack-allocated limb
(hence the word#), *or* an heap-allocated 'ByteArray#', which lead to
the MPZ# 3-tuple.
Ok, I see now. Thanks for the explanation.
Cheers,
Simon
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