eczn

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

eczn

参考自 https://github.com/digoal/blog/blob/master/202212/20221207_01.md 这里备份记录一下

---

第零步：关闭 SIP

SIP 会导致你即使是 root 用户也会出 operation not permitted 的情况出现，尤其是操作一些系统底层的时候（比如 nvram、系统目录/服务等）

关闭方式（只测了我的 m1 mac，需要进入恢复模式）：

1. 关机

eczn

%GetOptimizationStatus return a set of bitwise flags instead of a single value, to access the value, you need to take the binary representation of the returned value. Now, for example, if 65 is returned, the binary representation is the following:

(65).toString(2).padStart(12, '0');
// 000001000001

Each binary digit acts as a boolean with the following meaning:

eczn

Per https://code.google.com/p/v8/codesearch#v8/trunk/src/runtime.cc


%CreateSymbol
%CreatePrivateSymbol
%CreateGlobalPrivateSymbol
%NewSymbolWrapper
%SymbolDescription
%SymbolRegistry
%SymbolIsPrivate

eczn

enum Token {
  Value(Int)
  LParen;
  RParen;
  Plus;
  Minus;
  Multiply;
  Divide;
} derive(Debug)

eczn

;  ___           _        __ ___  __ ___
; / __|_ _  __ _| |_____ / /| __|/  \_  )
; \__ \ ' \/ _` | / / -_) _ \__ \ () / /
; |___/_||_\__,_|_\_\___\___/___/\__/___|

; An annotated version of the snake example from Nick Morgan's 6502 assembly tutorial
; on http://skilldrick.github.io/easy6502/ that I created as an exercise for myself
; to learn a little bit about assembly. I **think** I understood everything, but I may
; also be completely wrong :-)

eczn

/*
  UPDATED for 2023 - Now much simpler. The old tricks are no longer needed.

  The following code makes an 800×600 canvas that is always as sharp as possible for the device.

  You still draw on it as if it's the logical size (800×600 in this case), but everything just
  looks sharper on high-DPI screens. Regular non-sharp screens are not affected.
*/

const width = 800

eczn

import React from 'react';

/** createSignal for react */
export function createSignal<S>(
  initialState: S
): [() => S, (nextState: S) => void] {
  const forceRender = useForceRender();
  const stateRef = React.useRef<S>(initialState);
  const stateRefGetter = (): S => stateRef.current;

eczn

export enum Units {
  B = 1,
  KB = 1 * 1024,
  MB = 1 * 1024 * 1024,
  GB = 1 * 1024 * 1024 * 1024,
  TB = 1 * 1024 * 1024 * 1024 * 1024,
}

const UnitsName = ['B', 'KB', 'MB', 'GB', 'TB'];

eczn

/**
 * 实现任意 increment 的任意数字的 rounding 操作;
 * 比如 Math.round(n) 其实就是 genericRound(n, 1) 的特化
 */
export function genericRound(n: number, inc: number): number {
  if (inc === 0) return n;
  const d = (n % inc);
  if (d >= (inc / 2)) return n + (inc - d);
  return n - d;
}