Re: how io.read() will return nil ?

["Alexander Gladysh" <agladysh@...>]

> I think you want to test for empty string, that is not the same as nil.
> Try this one:
>
> for count = 1, math.huge do
>    local line = io.read()
>    if #line == 0 then break end
>    io.write(string.format("%6d ", count), line, "\n")
> end

A little note: this is kind of slower way to check if string is empty.
Fastest would be to compare with empty string constant:

for count = 1, math.huge do
   local line = io.read()
   if line == "" then break end
   io.write(string.format("%6d ", count), line, "\n")
end

Please note that the difference is quite small though (note 10^9 iterations).

Benchmarking results follow.

Legend: "empty" is test with line being empty string, "nonempty" --
with non-empty string. The "constant" is `line == ""`, "size" is
`#line == 0` and "upvalue" is comparison with upvalue, containing
empty string.

$ time lua estrbench.lua empty_constant 1000000000
      127.46 real       126.46 user         0.36 sys

$ time lua estrbench.lua empty_upvalue 1000000000
      134.89 real       133.78 user         0.42 sys

$ time lua estrbench.lua empty_size 1000000000
      141.92 real       140.77 user         0.42 sys


$ time lua estrbench.lua nonempty_constant 1000000000
      123.05 real       122.07 user         0.34 sys

$ time lua estrbench.lua nonempty_size 1000000000
      139.43 real       138.26 user         0.41 sys

$ time lua estrbench.lua nonempty_upvalue 1000000000
      164.73 real       163.36 user         0.48 sys


LuaJIT improves speed greatly


$ time luajit -O estrbench.lua empty_constant 1000000000
       18.22 real        17.90 user         0.08 sys

$ time luajit -O estrbench.lua empty_size 1000000000
       25.30 real        25.08 user         0.07 sys

$ time luajit -O estrbench.lua empty_upvalue 1000000000
       27.81 real        27.57 user         0.08 sys


$ time luajit -O estrbench.lua nonempty_constant 1000000000
       17.74 real        17.58 user         0.06 sys

$ time luajit -O estrbench.lua nonempty_upvalue 1000000000
       28.76 real        28.33 user         0.12 sys

$ time luajit -O estrbench.lua nonempty_size 1000000000
       25.53 real        25.10 user         0.10 sys


Benchmark attached, run it as

$ KBENCH_SCRIPT=estrbench.lua KBENCH_NUM_ITER=1000000000 ./kbench.sh

Sorry if my silly benchmarks are too nagging.

Alexander.

Attachment: kbench.sh
Description: Bourne shell script

Attachment: estrbench.lua
Description: Binary data