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Am 17.09.2010 02:40, schrieb liam mail:

On 16 September 2010 23:19, Mike Pall <> wrote:
Victor Poughon wrote:
> When running it until 1,000,000 it finishes in about 15 seconds. (I have a
> 1.83Ghz processor).
> I'm not really concerned about performance, and i'm sure there's a better
> algorithm for solving this problem. But an equivalent algorithm in
> C<>finishes about 6 times faster.
> Is this what one should expect from Lua ?

It runs 8.5x faster with LuaJIT.

Obviously algorithmic improvements pay off a lot here. The
following code takes 60 milliseconds on my machine with LuaJIT:

local bit = require("bit")
local bnot, bor, band = bit.bnot, bit.bor,
local shl, shr = bit.lshift, bit.rshift

local N = tonumber(arg and arg[1]) or 1000000
local cache, m, n = { 1 }, 1, 1
for i=2,N do
 local j = i
 for len=1,1000000000 do
   j = bor(band(shr(j,1), band(j,1)-1), band(shl(j,1)+j+1, bnot(band(j,1)-1)))
   local x = cache[j]; if x then j = x+len; break end
 cache[i] = j
 if j > m then m, n = j, i end
io.write("Found ", n, " (chain length: ", m, ")\n")


That code may well be faster but it is horrible code that someone learning the language should not have to look at.

To hard words. It is just to show that it is possible.
The bit operations are challenging me at the moment, but I'm very fine with the cache (very luaish, I think).
Mike, thank you  for the stimulation.