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  17. 26 Mar, 2018 7 commits
    • Rusty Russell's avatar
      intmap: add iterator-by-callback. · 1e888a93
      Rusty Russell authored 
      It's significantly faster because it assumes no deletion:

10000000,critbit iteration (nsec),316
10000000,critbit callback iteration (nsec),90
...
10000000,critbit consecutive iteration (nsec),308
10000000,critbit consecutive callback iteration (nsec),78
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      1e888a93
    • Rusty Russell's avatar
      intmap: add exhaustive testcases for intmap_after · a241664c
      Rusty Russell authored 
      We can't do the full range, but we can for a handful of bits (8).
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      a241664c
    • Rusty Russell's avatar
      intmap: add test case which failed, extracted from real world usage. · 4d9c7e1c
      Rusty Russell authored 
      Because intmap_after_() would simply examine the critbits to walk the
tree, it wouldn't realize that it might be in the completely wrong tree.

In this case:

         Bit 4:
         0   1
        /     \
       /       \
  100000011  100001011

When we ask for intmap_after_(011111111) we would check the critbit, it's
a 1, so we end up on the right leaf instead of the left.
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      4d9c7e1c
    • Rusty Russell's avatar
      intmap: reimplement so that intmap_after works. · e59acd52
      Rusty Russell authored 
      A critbit tree is a binary tree which keeps branches for each bit
which differs in the leaves.  It's a simple data structure, but not
entirely simple to implement the primitives people expect, as this bus
shows.

The bug: I added an open iterator, and intmap_after_ for a random
value would sometimes return the wrong node.

Cause: we don't know what the prefix is as we iterate, so by only
testing the critbits in the tree, we can end up in the wrong place.
This is only a problem if the value isn't in the (sub)tree, but this
can easily happen even with contiguous trees should deletion occur.
You can see an example in the next patch, which adds a test.

After finding a bug in my intmap_after() routine, I went searching for
other implementations to see how they handled it.  Most didn't provide
an open-ended iterator like this, relying on callback iterators which
don't allow deletion.  Gah!

The exception was https://github.com/blynn/blt/blob/master/blt.c#L179
which implements blt_ceil() which does this (if you add one to the
key, at least).  However, it does it by effectively finding a node,
using that to derive the prefix, then walking down the tree again.
That's pretty suboptimal.

There are basically two choices if you want an efficient after()
operation: to reimplement this approach with some optimizations
(ie. keep branches as we descend, and when we get to the bottom and
know the prefix, we know which branch to go down), or keep the bits
which got to each node.

The latter is more optimal, but less generally useful: for bit
strings, for example, we could keep the bits in common on each node,
rather than storing the entire string at the bottom.  But in practice
you'd be doing allocations to re-create the index if the caller wanted
it.

However, in this implementation our keys are 64 bits only, and we
already use a u8 for the bit number: using a 64-bit value there
consumes no more space (thanks to alignment).  We can store the
critbit by using the prefix capped by a bit: 0b10000...0000 means
no prefix and highest bit is the critbit, and 0bxxxxx1000...000
means the prefix is xxxxxx and the critbit is the 6th highest bit.

The penalty is that iteration 70% slower.  It's still pretty fast
though.

Before:
$ for i in `seq 5`; do ./speed 10000000; done | stats
10000000,random generation (nsec),3-4(3.2+/-0.4)
10000000,critbit insert (nsec),1530-1751(1633.2+/-80)
10000000,critbit successful lookup (nsec),1723-1993(1806.8+/-97)
10000000,critbit failed lookup (nsec),1763-2104(1933.6+/-1.3e+02)
10000000,critbit iteration (nsec),208-266(242.2+/-19)
10000000,critbit memory (bytes),48
10000000,critbit delete (nsec),1747-1861(1803.8+/-42)
10000000,critbit consecutive iteration (nsec),182-228(210+/-18)

After:
10000000,random generation (nsec),3-4(3.2+/-0.4)
10000000,critbit insert (nsec),1533-1699(1628+/-65)
10000000,critbit successful lookup (nsec),1831-2104(1972.4+/-1e+02)
10000000,critbit failed lookup (nsec),1850-2152(2008.2+/-1.1e+02)
10000000,critbit iteration (nsec),304-324(312.8+/-7.5)
10000000,critbit memory (bytes),48
10000000,critbit delete (nsec),1617-1872(1752+/-99)
10000000,critbit consecutive iteration (nsec),303-318(311+/-5.4)
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      e59acd52
    • Rusty Russell's avatar
      intmap: add benchmarks. · 82229812
      Rusty Russell authored 
      I wrote these a while ago, dig them out.

On my laptop, min-max(avg+/-stdev) of 5 runs:

make && for i in `seq 5`; do ./speed 10000000; done | stats
make: Nothing to be done for 'all'.
10000000,random generation (nsec),3-4(3.2+/-0.4)
10000000,critbit insert (nsec),1530-1751(1633.2+/-80)
10000000,critbit successful lookup (nsec),1723-1993(1806.8+/-97)
10000000,critbit failed lookup (nsec),1763-2104(1933.6+/-1.3e+02)
10000000,critbit iteration (nsec),208-266(242.2+/-19)
10000000,critbit memory (bytes),48
10000000,critbit delete (nsec),1747-1861(1803.8+/-42)
10000000,critbit consecutive iteration (nsec),182-228(210+/-18)
10000000,hash insert (nsec),396-424(412+/-9.6)
10000000,hash successful lookup (nsec),150-164(157.4+/-5.5)
10000000,hash failed lookup (nsec),163-178(170+/-5.5)
10000000,hash iteration (nsec),21-26(23.2+/-1.7)
10000000,hash memory (bytes),45
10000000,hash delete (nsec),179-194(183.6+/-5.3)
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      82229812
    • Rusty Russell's avatar
      bitops: new module. · eb10bf9f
      Rusty Russell authored 
      Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      eb10bf9f
    • Rusty Russell's avatar
      configurator: add tests for other popcount variants. · d872b7f2
      Rusty Russell authored 
      Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      d872b7f2
  19. 16 Mar, 2018 1 commit
    • Jan Sarenik's avatar
      Makefile: Fix asort multiple definition error · 7a75cff7
      Jan Sarenik authored 
      Error I experienced on Alpine Linux without this patch:

    In file included from ccan/generator/generator.c:8:0:
    ./ccan/generator/generator.h:23:2: error: #error Generators require coroutines
     #error Generators require coroutines
      ^~~~~
    make: *** [Makefile:32: ccan/generator/generator.o] Error 1
      7a75cff7
  21. 14 Mar, 2018 2 commits
  23. 01 Mar, 2018 1 commit
  25. 26 Feb, 2018 2 commits
  27. 16 Feb, 2018 1 commit
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  35. 25 Oct, 2017 1 commit
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