| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry; Jodorowsky; Tomato Chutney; Analysis of Support for Trump; Indian SF; TP-Link TL-WR841N DNS TCP Bug; TP-Link TL-WR841N as Wireless Bridge; Sending Email On Time; Maybe run a command; Sterile Neutrinos; Strawberry and Banana Jam; The Best Of All Possible Worlds; Kenzaburo Oe: The Changeling; Peach Jam; Taste Test; Strawberry and Raspberry Jam; flac to mp3 on OpenSuse 42.1; Also, Sebald; Kenzaburo Oe Interview; Otake (Kitani Minoru) move Black 121; Is free speech in British universities under threat?; I am actually good at computers; Was This Mansplaining?; WebFaction / LetsEncrypt / General Disappointment; Sensible Philosophy of Science; George Ellis; Misplaced Intuition and Online Communities; More Reading About Japan; Visibilty / Public Comments / Domestic Violence; Ferias de Santiago; More (Clearly Deliberate); Deleted Obit Post; And then a 50 yo male posts this...; We Have Both Kinds Of Contributors; Free Springer Books; Books on Religion; Books on Linguistics; Palestinan Electronica; Books In Anthropology; Taylor Expansions of Spacetime; Info on Juniper; Efficient Stream Processing; The Moral Character of Crypto; Hearing Aid Info; Small Success With Go!; Re: Quick message - This link is broken; Adding Reverb To The Echo Chamber; Sox Audio Tools; Would This Have Been OK?; Honesty only important economically before institutions develop; Stegangraphy via PS4; OpenCL Mess

© 2006-2015 Andrew Cooke (site) / post authors (content).

40-fold Speedup in LEPL Parsing

From: "andrew cooke" <andrew@...>

Date: Fri, 6 Mar 2009 19:51:54 -0300 (CLST)

OK, so this was a somewhat extreme test case, but by rearranging the
grammar I can make it more likely to terminate and so avoid lots of
pointless recursion.  Here's the code that does the rewriting - I'm
pleased at how simple it is, after all the work making matchers graphs,
etc:

def optimize_or(graph):
  '''
  When a left-recursive rule is used, it is much more efficient
  if it appears last in an `Or` statement, since that forces the
  alternates (which correspond to the terminating case in a
  recursive function) to be tested before the LMemo limit is
  reached.

  This rewriting may change the order in which different results
  for an ambiguous grammar are returned.
  '''
  for delayed in [x for x in preorder(graph)
                  if type(x) is Delayed]:
    for loop in loops(delayed):
      for i in range(len(loop)):
        if isinstance(loop[i], Or):
          # we cannot be at the end of the list here,
          # since that is a Delayed instance
          matchers = loop[i].matchers
          target = loop[i+1]
          # move target to end of list
          index = matchers.index(target)
          del matchers[index]
          matchers.append(target)
  return graph

Even on a more reasonable case (the LMemo example in the docs), the
speedup is about a factor of 2 (that includes some additional tweaks
elsewhere).

It's surprising how uniform the profiles are (the flip side of that is
that there's little to optimise from a code-tweaking pov).  The only other
improvement I can think of at the moment is adding a tokenizer (which will
allow LMemo lookahead to use larger "chunks", advancing by words rather
than letters).

Andrew

Comment on this post