Arrays oddities
- From: Alain Meunier <deco33@xxxxxxxxxx>
- To: "luajit@xxxxxxxxxxxxx" <luajit@xxxxxxxxxxxxx>
- Date: Mon, 31 Mar 2014 11:04:51 +0200
Hello,
Questions :
1) Why can we allocate a value in an array out of the bound ?
local ffi = require "ffi"
local bytes = ffi.new("int[2]")
bytes[2] = 4
bytes[5] = 8
print(bytes[5])
2) Should not an array be faster than a table ?
Io has its part but redoing the same with a lorem ipsum is always me the same
results
ffi version slower by ~8% / table version.
ffi array version :
local ffi = require "ffi"
local bytes = ffi.new("int[7281624]")
local io_lines_override,tonumber_override = io.lines,tonumber
local f = io_lines_override ("myfile.txt")
local iterator = 0
for line in f do
bytes[iterator] = tonumber_override(line)
iterator = iterator + 1
end
for ii = 0, 7281624 do bytes[ii] = bytes[ii] + 1 end
-------------------------------------------------------------------------------------------
Table version :
local junction_sentinel = {}
local io_lines_override,tonumber_override = io.lines,tonumber
local f = io_lines_override ("myfile.txt")
local iterator = 1
for line in f do
junction_sentinel[iterator] = tonumber_override(line)
iterator = iterator + 1
end
for ii = 1, 7281624 do junction_sentinel[ii] = junction_sentinel[ii] + 1 end
3) Last but not least, -O3 and fast-math helped to improve some random codes
(cannot be published) by several seconds (~15 seconds average on a broadly
1.30-2 min very intensive runtime). But not really safe. That is Good. 2.0.3
is faster but 2.1 much slower (100% slower) on these codes. Will look into a
publishable code to reproduce it.
Other related posts:
