json VS simdjson

I have not done a "desktop" program in 25+ years and never using C++ (or C), since then I'm mostly a web developer (PHP,Elixir, JS, Kotlin etc).

I'm currently doing a C++ audio plugin with the Juce framework.

This website has been a good resource, alongside https://www.learncpp.com

But I was actually close to give up before using those two things:

- https://github.com/nlohmann/json : my plugin use a json api backend and the Juce json implementation is atrocious (apparently because of being born in previous c++ version), but this library is GREAT.

- ChatGPT 4. I'm not sure I would have "succeeded" without it, at least not in a reasonable time frame. ChatGPT 3.5 is slow and does not give good results for my use case but 4 is impressive. And I use in a very dumb way, just posing question in the web UI. I probably could have it directly in MSVC?

Also I must say, for all its flaws, I have a renewed appreciation for doing UI on the web ;)

https://github.com/nlohmann/json works well for me

cmake_minimum_required(VERSION 3.15) project(xrpc++ DESCRIPTION "C++ AT Protocol XRPC library" VERSION 1.0.0 LANGUAGES CXX) include(FetchContent) FetchContent_Declare(cpr GIT_REPOSITORY https://github.com/libcpr/cpr.git GIT_TAG 2553fc41450301cd09a9271c8d2c3e0cf3546b73) # The commit hash for 1.10.x. Replace with the latest from: https://github.com/libcpr/cpr/releases FetchContent_MakeAvailable(cpr) FetchContent_Declare(json URL https://github.com/nlohmann/json/releases/download/v3.11.2/json.tar.xz) FetchContent_MakeAvailable(json) add_library(${PROJECT_NAME} SHARED src/lexicon.cpp src/xrpc.cpp ) target_link_libraries(${PROJECT_NAME} PRIVATE cpr::cpr) target_link_libraries(${PROJECT_NAME} PRIVATE nlohmann_json::nlohmann_json) set_target_properties(${PROJECT_NAME} PROPERTIES VERSION ${PROJECT_VERSION}) set_target_properties(${PROJECT_NAME} PROPERTIES SOVERSION 1) target_include_directories(${PROJECT_NAME} PUBLIC include) set(CMAKE_BUILD_TYPE debug)

FetchContent_Declare(json URL https://github.com/nlohmann/json/releases/download/v3.11.2/json.tar.xz) FetchContent_MakeAvailable(json)

Here is one popular C++ library (nlohmann/json) removing its use.

Before going into binary serialization I suggest you to get comfortable with serialization to text. You can try to write your data to text files and read them in again. Then after you get an idea of how this works you can try to use a library that writes to XML or json, e.g. nlohmann json

Download the single header file json.hpp from https://github.com/nlohmann/json/releases and place it in your project directory or an include directory.

Exemple of a JSON library: https://github.com/nlohmann/json (For XML, there's tinyxml)

String parsing is negligible compared to the speed of the DOM which is glacially slow: https://news.ycombinator.com/item?id=38835920

Come on, people, make an effort to learn how insanely fast computers are, and how insanely inefficient our software is.

String parsing can be done at gigabytes per second: https://github.com/simdjson/simdjson If you think that is the slowest operation in the browser, please find some resources that talk about what is actually happening in the browser?

Thanks for all the detailed information! That answers a bunch of my questions and the implementation of strlen is nice.

The instruction I was thinking of is pshufb. An example ‘weird’ use can be found for detecting white space in simdjson: https://github.com/simdjson/simdjson/blob/24b44309fb52c3e2c5...

This works as follows:

1. Observe that each ascii whitespace character ends with a different nibble.

2. Make some vector of 16 bytes which has the white space character whose final nibble is the index of the byte, or some other character with a different final nibble from the byte (eg first element is space =0x20, next could be eg 0xff but not 0xf1 as that ends in the same nibble as index)

3. For each block where you want to find white space, compute pcmpeqb(pshufb(whitespace, input), input). The rules of pshufb mean (a) non-ascii (ie bit 7 set) characters go to 0 so will compare false, (b) other characters are replaced with an element of whitespace according to their last nibble so will compare equal only if they are that whitespace character.

I’m not sure how easy it would be to do such tricks with vgather.vv. In particular, the length of the input doesn’t matter (could be longer) but the length of white space must be 16 bytes. I’m not sure how the whole vlen stuff interacts with tricks like this where you (a) require certain fixed lengths and (b) may have different lengths for tables and input vectors. (and indeed there might just be better ways, eg you could imagine an operation with a 256-bit register where you permute some vector of bytes by sign-extending the nth bit of the 256-bit register into the result where the input byte is n).

Additionally, if you like low level stuff, check out libfmt (https://github.com/fmtlib/fmt) - not a big project, not difficult to understand. Or something like simdjson (https://github.com/simdjson/simdjson).

Everything you said is totally reasonable. I'm a big fan of napkin math and theoretical upper bounds on performance.

simdjson (https://github.com/simdjson/simdjson) claims to fully parse JSON on the order of 3 GB/sec. Which is faster than OP's Go whitespace parsing! These tests are running on different hardware so it's not apples-to-apples.

The phrase "cannot go faster than this" is just begging for a "well ackshully". Which I hate to do. But the fact that there is an existence proof of Problem A running faster in C++ SIMD than OP's Probably B scalar Go is quite interesting and worth calling out imho. But I admit it doesn't change the rest of the post.

I have same question as /u/JDRiverRun : how do you deal with JSON, do you parse json on Rust side or on Emacs side. I see that you are requiring json.el in your lspce.el, but I haven't looked through entire file carefully. If you parse on Rust side, do you use simdjson (there are at least two Rust bindings to it)? If yes, what are your impressions, experiences compared to more "standard" json library?

I expect a lot of transcoders will be rewritten when the Vector instructions land. You can see speedups when used in other languages, such as simdjson. Please try to be more thoughtful and not disregard other people's hard work so easily.