Schrodinger ZHU Yifan SchrodingerZhu

UCRT Notes

Background

At LLVM libc, I am exploring a harder approach (than MinGW) to implement a brand new CRT. As such, I am reading the UCRT code (open sourced portion). This document is for recording some interesting findings I have come across in the codebase. I will also write down some thoughts that might be useful for future implementation, which does not restrict to the UCRT codebase.

The code is from https://www.nuget.org/packages/Microsoft.Windows.SDK.CRTSource.

	module Main (main) where

	import Data.HashMap.Strict qualified as H
	import Data.Maybe (isJust)
	import Data.Graph (stronglyConnComp, SCC(..), flattenSCC)
	import Data.List (intercalate, nub)

	-- See: https://dl.acm.org/doi/pdf/10.1145/3720472

	data Type

	//===-- Implementation header for weak AVL tree ------------------ C++ --===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//
	// Weak AVL tree implementation based on the algorithm described in:
	// 1. https://maskray.me/blog/2025-12-14-weak-avl-tree
	// 2. https://reviews.freebsd.org/D25480

	struct Lancern;

	struct QuaticCat;

	struct Float;

	union Union;

	struct Lancern
	{

	[nix-shell:~/CLionProjects/paguroidea]$ env RUSTFLAGS="-C target-cpu=native" PAG_RANDOM_SEED=0 cargo bench
	Compiling snmalloc-sys v0.3.3
	Compiling pag-lexer v0.1.0-alpha.1 (/home/schrodinger/CLionProjects/paguroidea/pag-lexer)
	Compiling serde_derive v1.0.163
	Compiling lalrpop v0.20.0
	Compiling pest_meta v2.6.0
	Compiling pest_generator v2.6.0
	Compiling pest_derive v2.6.0
	Compiling pag-parser v0.1.0-alpha.1 (/home/schrodinger/CLionProjects/paguroidea/pag-parser)
	Compiling serde v1.0.163

	// Type your code here, or load an example.
	pub fn square(num: i32) -> i32 {
	num * num
	}

	// If you use `main()`, declare it as `pub` to see it in the output:
	// pub fn main() { ... }
	pub mod parser {
	extern crate alloc;
	#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]

	#![no_std]
	extern crate alloc;

	use alloc::rc::Rc;
	use core::cell::UnsafeCell;
	use core::ptr::NonNull;

	struct Node {
	tree_parent: Option<NonNull<Self>>,
	tree_left: Option<NonNull<Self>>,

	#![feature(core_intrinsics)]

	use std::intrinsics::likely;
	use std::marker::PhantomData;
	use std::ptr::NonNull;
	use std::rc::{Rc, Weak};

	struct Node<T> {
	next: NonNull<Self>,
	prev: NonNull<Self>,