simon-git: spigot (master): spigot.git

[Commits to Tartarus hosted VCS]

TL;DR:
  2793ace Handle exact integer cases of log2 and log10.

Repository:     https://git.tartarus.org/simon/spigot.git
On the web:     https://git.tartarus.org/?p=simon/spigot.git
Branch updated: master
Committer:      spigot.git
Date:           2016-10-31 20:49:32

commit 2793ace18dca363201040a20dc07247752af17da
web diff https://git.tartarus.org/?p=simon/spigot.git;a=commitdiff;h=2793ace18dca363201040a20dc07247752af17da;hp=3e177c2b46f8963b630d1d16421abdff69f05ec5
Author: Simon Tatham <anakin at pobox.com>
Date:   Mon Oct 31 20:44:57 2016 +0000

    Handle exact integer cases of log2 and log10.
    
    I had occasion today to need log2() to recognise an exact power of 2
    and return the result, and annoyingly, it didn't, and instead hung on
    an exactness hazard.
    
    The fix for log2 could be more efficient, in that I could have
    recognised a power of 2 in the numerator or denominator of a rational
    via bit-twiddling of the form (x & (x-1)) == 0. But I prefer doing it
    using the spigot system itself, because then it adapts trivially to
    other bases, so I get to do log10 the same way.
    
    (Indeed, this way I could even expose a two-operand log_b(a) function
    to the user, which would probably be able to spot any case in which b
    is rational and a is an integer power of it. Though I suppose it would
    be harder to spot _rational_ powers of it - you'd also want, for
    example, log_100(10) to return 1/2, and that might be tricker.)

 exp.cpp | 53 +++++++++++++++++++++++++++++++++++++++++++++++++----
 test.sh | 18 ++++++++++++++++++
 2 files changed, 67 insertions(+), 4 deletions(-)