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Javad Shafique cjavad

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o11c / every-vm-tutorial-you-ever-studied-is-wrong.md
Last active November 1, 2025 03:21
Every VM tutorial you ever studied is wrong (and other compiler/interpreter-related knowledge)

Note: this was originally several Reddit posts, chained and linked. But now that Reddit is dying I've finally moved them out. Sorry about the mess.


URL: https://www.reddit.com/r/ProgrammingLanguages/comments/up206c/stack_machines_for_compilers/i8ikupw/ Summary: stack-based vs register-based in general.

There are a wide variety of machines that can be described as "stack-based" or "register-based", but not all of them are practical. And there are a lot of other decisions that affect that practicality (do variables have names or only address/indexes? fixed-width or variable-width instructions? are you interpreting the bytecode (and if so, are you using machine stack frames?) or turning it into machine code? how many registers are there, and how many are special? how do you represent multiple types of variable? how many scopes are there(various kinds of global, local, member, ...)? how much effort/complexity can you afford to put into your machine? etc.)

  • a pure stack VM can only access the top elemen
@cjavad
cjavad / M11.js
Last active May 24, 2022 19:16
Module 11 integration in javascript/nodejs with 18 integers
// M11.js
/*
* Modules 11 control algorithm it's used
* Used by the danish goverment to validate CPR numbers (social security numbers).
* It works by having a number list and giving them each a weight from 2 to 7 then
* multiplying them to then divide the number with the mod (11 usually)
* to see if the reminder is 0.
*
* the modules operator (%) in javascript takes bad values.