[commit: packages/integer-gmp] wip/T8647: Allocate initial 1-limb mpz_t on the Stack and introduce MPZ# type (20d7bfd)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/integer-gmp

On branch  : wip/T8647
Link       : http://ghc.haskell.org/trac/ghc/changeset/20d7bfdd29917f5a8b8937fba9b724f7e71cd8dd/integer-gmp

>---------------------------------------------------------------

commit 20d7bfdd29917f5a8b8937fba9b724f7e71cd8dd
Author: Herbert Valerio Riedel <hvr at gnu.org>
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.
    
    In order to delay heap allocations of 1-limb `ByteArray#`s instead of
    the previous `(# Int#, ByteArray# #)` pair, a 3-tuple
    `(# Int#, ByteArray#, Word# #)` is returned now. This tuple is given the
    type-synonym `MPZ#`.
    
    This 3-tuple representation uses either the 1st and the 2nd element, or
    the 1st and the 3rd element to represent the limb(s) (NB: undefined
    `ByteArray#` elements must not be accessed as they don't point to a
    proper `ByteArray#`, see also `DUMMY_BYTE_ARR`); more specifically, the
    following encoding is used (where `⊥` means undefined/unused):
    
     -  (#  0#, ⊥, 0## #) -> value = 0
     -  (#  1#, ⊥, w   #) -> value = w
     -  (# -1#, ⊥, w   #) -> value = -w
     -  (#  s#, d, 0## #) -> value = J# s d
    
    The `mpzToInteger` helper takes care of converting `MPZ#` into an
    `Integer`, and allocating a 1-limb `ByteArray#` in case the
    value (`w`/`-w`) doesn't fit the `S# Int#` representation).
    
    The following nofib benchmarks benefit from this optimization:
    
            Program      Size    Allocs   Runtime   Elapsed  TotalMem
     ------------------------------------------------------------------
         bernouilli     +0.2%     -5.2%      0.12      0.12     +0.0%
             gamteb     +0.2%     -1.7%      0.03      0.03     +0.0%
              kahan     +0.3%    -13.2%      0.17      0.17     +0.0%
             mandel     +0.2%    -24.6%      0.04      0.04     +0.0%
              power     +0.2%     -2.6%     -2.0%     -2.0%     -8.3%
          primetest     +0.1%    -17.3%      0.06      0.06     +0.0%
                rsa     +0.2%    -18.5%      0.02      0.02     +0.0%
                scs     +0.1%     -2.9%     -0.1%     -0.1%     +0.0%
             sphere     +0.3%     -0.8%      0.03      0.03     +0.0%
             symalg     +0.2%     -3.1%      0.01      0.01     +0.0%
     ------------------------------------------------------------------
                Min     +0.1%    -24.6%     -4.6%     -4.6%     -8.3%
                Max     +0.3%     +0.0%     +5.9%     +5.9%     +4.5%
     Geometric Mean     +0.2%     -1.0%     +0.2%     +0.2%     -0.0%
    
    Signed-off-by: Herbert Valerio Riedel <hvr at gnu.org>


>---------------------------------------------------------------

20d7bfdd29917f5a8b8937fba9b724f7e71cd8dd
 GHC/Integer/GMP/Prim.hs |   88 ++++++++++++-------
 GHC/Integer/Type.lhs    |  160 +++++++++++++++------------------
 cbits/gmp-wrappers.cmm  |  224 +++++++++++++++++++++++++++++++++--------------
 3 files changed, 285 insertions(+), 187 deletions(-)

Diff suppressed because of size. To see it, use:

    git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc 20d7bfdd29917f5a8b8937fba9b724f7e71cd8dd