# Https://marioarias.hashnode.dev/a-response-to-the-luajit-is-wicked-fast-video **URL:** \ **Category:** News\ **Tags:** blog\ **Created:** [August 4, 2025, 6:31pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312 "2025-08-04T18:31:48Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![MarioAriasC](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/marioariasc/32/1434_2.png) [@MarioAriasC](https://forum.crystal-lang.org/u/MarioAriasC)\ **Post date:** [August 4, 2025, 6:31pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/1 "2025-08-04T18:31:48Z")
[https://marioarias.hashnode.dev/a-response-to-the-luajit-is-wicked-fast-video](https://marioarias.hashnode.dev/a-response-to-the-luajit-is-wicked-fast-video) A short blogpost about luajit, C and Crystal ---
**Author:** ![HertzDevil](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/hertzdevil/32/1023_2.png) [@HertzDevil](https://forum.crystal-lang.org/u/HertzDevil)\ **Post date:** [August 4, 2025, 7:53pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/2 "2025-08-04T19:53:20Z")
I tried this with Clang 18 and Crystal 1.17.0 on Debian, which too has LLVM 18. I got very different results: ```auto $ hyperfine -w 3 ./clangimg Benchmark 1: ./clangimg Time (mean ± σ): 180.9 ms ± 3.5 ms [User: 180.1 ms, System: 0.8 ms] Range (min … max): 176.2 ms … 187.2 ms 16 runs $ hyperfine -w 3 ./crystalimg Benchmark 1: ./crystalimg Time (mean ± σ): 213.1 ms ± 3.2 ms [User: 211.6 ms, System: 1.5 ms] Range (min … max): 208.7 ms … 222.4 ms 14 runs ``` But also I wouldn’t expect Crystal to be significantly faster than Clang for simply using LLVM. ---
**Author:** ![yxhuvud](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/yxhuvud/32/27_2.png) [@yxhuvud](https://forum.crystal-lang.org/u/yxhuvud)\ **Post date:** [August 4, 2025, 8:36pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/3 "2025-08-04T20:36:57Z")
Yeah, I’d expect the crystal code to compile to essentially the same as the c code here, except it also do a bunch of overflow checks. Which match up with the results hertzdevil got. ---
**Author:** ![ralsina](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/ralsina/32/2139_2.png) [@ralsina](https://forum.crystal-lang.org/u/ralsina)\ **Post date:** [August 4, 2025, 8:42pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/4 "2025-08-04T20:42:05Z")
You can compare all the versions with a single command: ```auto hyperfine --warmup 3 -m 50 ./clangimg ./clangimg-mc ./crystalimg ./gccimg ./gccimg-mc ``` In my case: ```auto Summary./crystalimg ran 1.13 ± 0.02 times faster than ./gccimg 1.14 ± 0.02 times faster than ./clangimg 1.19 ± 0.02 times faster than ./gccimg-mc 1.23 ± 0.02 times faster than ./clangimg-mc ``` ---
**Author:** ![ralsina](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/ralsina/32/2139_2.png) [@ralsina](https://forum.crystal-lang.org/u/ralsina)\ **Post date:** [August 4, 2025, 8:52pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/5 "2025-08-04T20:52:33Z")
Also, may I point out that at least in the crystal version f is 0 so all the pixels are set to 0, so all the green bits in image\_ramp\_green are 0, and all the rgb values are also 0, and they convert to a grey value of 0, so the code doesn’t actually DO anything? ---
**Author:** ![HertzDevil](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/hertzdevil/32/1023_2.png) [@HertzDevil](https://forum.crystal-lang.org/u/HertzDevil)\ **Post date:** [August 4, 2025, 9:51pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/6 "2025-08-04T21:51:28Z")
Looking at the snippet, _none_ of the `img[i].*` assignments do anything, because those are local copies on the stack. ---
**Author:** ![MarioAriasC](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/marioariasc/32/1434_2.png) [@MarioAriasC](https://forum.crystal-lang.org/u/MarioAriasC)\ **Post date:** [August 4, 2025, 11:59pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/8 "2025-08-04T23:59:16Z")
All you guys are pointing out that my code doesn’t do anything (and I was suspecting it), but why does following the same semantics and pattern of two other languages (which I consider natural) lead to different results, and if so, what will be the correct version? ---
**Author:** ![ralsina](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/ralsina/32/2139_2.png) [@ralsina](https://forum.crystal-lang.org/u/ralsina)\ **Post date:** [August 5, 2025, 11:04am UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/9 "2025-08-05T11:04:34Z")
At least for the value of f, for the code to make sense you should not cast to int at that point, since it’s a very small value and will be 0 I have not even looked at the other versions. ---
**Author:** ![ralsina](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/ralsina/32/2139_2.png) [@ralsina](https://forum.crystal-lang.org/u/ralsina)\ **Post date:** [August 5, 2025, 12:52pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/10 "2025-08-05T12:52:51Z")
The C code at least seems to actually keep the f value. So I modified the crystal one to be equivalent in that aspect. Also added the missing assignment to `img[i].alpha`, and made the `image_to_grey` values the same, then ran them via hyperfine: ```auto struct RGBPixel property red, blue, green, alpha def initialize(@red : UInt8 = 0, @blue : UInt8 = 0, @green : UInt8 = 0, @alpha : UInt8 = 255) end end def image_ramp_green(n) img = Array.new(n) { RGBPixel.new } f = 255.0/(n - 1) (0...n).each { |i| img[i].green = (i * f).to_u8 img[i].alpha = 255 } img end def image_to_gray(img, n) (0...n).each do |i| y = (0.3 * img[i].red + 0.59 * img[i].green + 0.1 * img[i].blue).to_u8 img[i].red = y img[i].green = y img[i].blue = y end end N = 400 * 400 img = image_ramp_green(N) (0...1000).each { image_to_gray(img, N) } ``` ```auto > hyperfine --warmup 3 -m 50 ./crystalimg ./clangimg Benchmark 1: ./crystalimg Time (mean ± σ): 223.2 ms ± 2.0 ms [User: 220.4 ms, System: 1.4 ms] Range (min … max): 220.0 ms … 229.4 ms 50 runs Benchmark 2: ./clangimg Time (mean ± σ): 255.5 ms ± 3.0 ms [User: 253.2 ms, System: 0.9 ms] Range (min … max): 249.9 ms … 267.0 ms 50 runs Summary ./crystalimg ran 1.14 ± 0.02 times faster than ./clangimg ``` I suspect it could be made much faster using some sort of SIMD vectorization tho ;-) ---
**Author:** ![HertzDevil](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/hertzdevil/32/1023_2.png) [@HertzDevil](https://forum.crystal-lang.org/u/HertzDevil)\ **Post date:** [August 5, 2025, 2:06pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/11 "2025-08-05T14:06:48Z")
All the time is spent on the overflow checks in the `#to_u8` calls. If we replace them with `#to_u8!`, we get this result: ```auto Benchmark 1: ./crystalimg Time (mean ± σ): 1.7 ms ± 0.2 ms [User: 1.2 ms, System: 0.5 ms] Range (min … max): 1.5 ms … 2.6 ms 552 runs Warning: Command took less than 5 ms to complete. Note that the results might be inaccurate because hyperfine can not calibrate the shell startup time much more precise than this limit. You can try to use the `-N`/`--shell=none` option to disable the shell completely. Benchmark 2: ./clangimg Time (mean ± σ): 126.6 ms ± 0.5 ms [User: 125.1 ms, System: 1.1 ms] Range (min … max): 126.1 ms … 128.0 ms 23 runs Summary ./crystalimg ran 72.62 ± 7.56 times faster than ./clangimg ``` which is exactly what I meant: the assignments are no-ops, since `img[i]` copies the pixel to the stack. The following is much closer: (note that `img[i] = img[i].copy_with(...)` creates two bounds checks as the array cannot be proved to remain unchanged inbetween) ```crystal record RGBPixel, red : UInt8 = 0, green : UInt8 = 0, blue : UInt8 = 0, alpha : UInt8 = 0 def image_ramp_green(n) img = Array.new(n) { RGBPixel.new } f = 255.0/(n - 1) (0...n).each do |i| img.update(i, &.copy_with( green: (i * f).to_u8!, alpha: 255_u8, )) end img end def image_to_gray(img, n) (0...n).each do |i| y = (0.3 * img[i].red + 0.59 * img[i].green + 0.1 * img[i].blue).to_u8! img.update(i, &.copy_with( red: y, green: y, blue: y, )) end end N = 400 * 400 img = image_ramp_green(N) (0...1000).each { image_to_gray(img, N) } ``` ```auto Summary ./clangimg ran 1.25 ± 0.01 times faster than ./crystalimg ``` The remaining difference is the double indirection in `Array` for the `img` variable; if we use a `Slice` instead, the Crystal and C versions will run at the same speed. ---
**Author:** ![MarioAriasC](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/marioariasc/32/1434_2.png) [@MarioAriasC](https://forum.crystal-lang.org/u/MarioAriasC)\ **Post date:** [August 5, 2025, 6:02pm UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/12 "2025-08-05T18:02:44Z")
I wrote a version that modifies the struct contents and it has similar performance ---
**Author:** ![MarioAriasC](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/marioariasc/32/1434_2.png) [@MarioAriasC](https://forum.crystal-lang.org/u/MarioAriasC)\ **Post date:** [August 9, 2025, 7:18am UTC](https://forum.crystal-lang.org/t/https-marioarias-hashnode-dev-a-response-to-the-luajit-is-wicked-fast-video/8312/13 "2025-08-09T07:18:24Z")
I updated the article with a correction. Sorry for the fake news [https://marioarias.hashnode.dev/a-response-to-the-luajit-is-wicked-fast-video](https://marioarias.hashnode.dev/a-response-to-the-luajit-is-wicked-fast-video)