simon-git: spigot (master): Simon Tatham

[Commits to Tartarus CVS repository.]

TL;DR:
  98e611f Deferred enforcement of range checks.
  2fcb4ed Explicitly specify direction in spigot_monotone_invert.
  28292a6 Add a special case for the lower bound when computing Wn.
  0ecb941 Document the exactness hazard in W/Wn as fixed.

Repository:     git://git.tartarus.org/simon/spigot.git
On the web:     http://tartarus.org/~simon-git/gitweb/?p=spigot.git
Branch updated: master
Committer:      Simon Tatham <anakin at pobox.com>
Date:           2015-04-18 14:28:13

commit 98e611f3e275cdea54f296a77b60954a445fcb03
web diff http://tartarus.org/~simon-git/gitweb/?p=spigot.git;a=commitdiff;h=98e611f3e275cdea54f296a77b60954a445fcb03;hp=5c034ab778c16b6cbfe319f9a7dbf9b1bccd2571
Author: Simon Tatham <anakin at pobox.com>
Date:   Wed Dec 31 10:59:44 2014 +0000

    Deferred enforcement of range checks.
    
    The range check against -1/e in lambertw.cpp is unusual for having an
    irrational bound, and therefore introducing an exactness hazard during
    the bounds check if the input value is exactly -1/e. Fixed by
    introducing a new 'spigot_enforce' wrapper, which acts as the identity
    function on its input number, but also continues to check it against a
    provided bound as more detail is computed, and throws an exception
    later in computation if the bound turns out to be violated.
    
    This doesn't fix the exactness hazard in W(-1/e) by itself; there's a
    second hazard at the same place, which I'll fix next.

 Makefile.am     |    4 +--
 enforce.cpp     |   80 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 error.h         |   14 ++++++++++
 lambertw.cpp    |   28 +++++++++++++++++--
 python/setup.py |    1 +
 5 files changed, 123 insertions(+), 4 deletions(-)

commit 2fcb4ed156fe756542da2719b9b8fa2110c5de08
web diff http://tartarus.org/~simon-git/gitweb/?p=spigot.git;a=commitdiff;h=2fcb4ed156fe756542da2719b9b8fa2110c5de08;hp=98e611f3e275cdea54f296a77b60954a445fcb03
Author: Simon Tatham <anakin at pobox.com>
Date:   Sat Apr 18 14:17:37 2015 +0100

    Explicitly specify direction in spigot_monotone_invert.
    
    Sometimes the output value of spigot_monotone_invert turns out to be
    _at_ one of the endpoints, in which case the initial sign check that
    expected f(x)-t to have opposite signs at the endpoints would have
    caused an exactness hazard.
    
    That sign check was pure laziness on my part, so that callers of
    spigot_monotone_invert wouldn't have to deduce from theory whether
    their function was increasing or decreasing. Now they do have to say
    that (which isn't hard anyway), so spigot_monotone_invert can lose
    that initial hazardous sign test. (They now also have to provide their
    interval bounds in the right order, but that's less vital.)
    
    As a result, W(-1/e) is now no longer an exactness hazard, although
    Wn(-1/e) still is (for yet a third reason).

 erf.cpp      |    3 ++-
 funcs.h      |    2 +-
 lambertw.cpp |    6 +++---
 monotone.cpp |   45 +++++++++++++++++++--------------------------
 test.sh      |    1 +
 5 files changed, 26 insertions(+), 31 deletions(-)

commit 28292a6f1297a5e46a3297cfe128aaab39726a1c
web diff http://tartarus.org/~simon-git/gitweb/?p=spigot.git;a=commitdiff;h=28292a6f1297a5e46a3297cfe128aaab39726a1c;hp=2fcb4ed156fe756542da2719b9b8fa2110c5de08
Author: Simon Tatham <anakin at pobox.com>
Date:   Sat Apr 18 08:36:19 2015 +0100

    Add a special case for the lower bound when computing Wn.
    
    If we're asked for Wn(-1/e), we can't find a number between -1 and the
    right answer to use as the interval upper bound, so we have to fall
    back to using -1 itself as the interval bound in that situation.

 lambertw.cpp |   23 +++++++++++++++++++----
 test.sh      |    1 +
 2 files changed, 20 insertions(+), 4 deletions(-)

commit 0ecb9419d89a5fb57cdad4fb10c29c13bc292257
web diff http://tartarus.org/~simon-git/gitweb/?p=spigot.git;a=commitdiff;h=0ecb9419d89a5fb57cdad4fb10c29c13bc292257;hp=28292a6f1297a5e46a3297cfe128aaab39726a1c
Author: Simon Tatham <anakin at pobox.com>
Date:   Sat Apr 18 14:17:46 2015 +0100

    Document the exactness hazard in W/Wn as fixed.

 manpage.but |    7 +++----
 manual.but  |   11 +++--------
 2 files changed, 6 insertions(+), 12 deletions(-)