kissa.bsky.social
@kissa.bsky.social
Tomfoolery, nincompoopery, programming
37 followers374 following39 posts
First we need memory. 64kB will be nice. And the ability to read a word from the memory. Word is 16 bits.
![const MEM_SIZE = 256 * 256
const mem = new Uint8Array(MEM_SIZE)
function error(msg: string) {
throw new Error(msg)
}
function read(addr: number) {
if (addr < 0 || addr >= MEM_SIZE) {
error(`read: invalid address ${addr}`)
}
return (mem[addr] << 8) + mem[addr + 1]
}
function test() {
mem[0] = 0x12
mem[1] = 0x34
console.log(`0x${read(0).toString(16)}`)
// => 0x1234
}
test()](https://cdn.bsky.app/img/feed_fullsize/plain/did:plc:ih3rt6r3sesh2flndp7oefwc/bafkreihkvwchojjua2eevelotcsa6onmsn4v4pwwtoddmb74h54kqi2qwi@jpeg)
There's a bug in the above code. Reading at address 65535 should work, and let's make it so that the memory wraps (in practice rarely happens, but details matter)
![index.test.ts:
✓ read word from memory [0.06ms]
12 |
13 | test("read at memory boundary", () => {
14 | mem[MEM_SIZE - 1] = 0x98
15 | mem[0] = 0x76
16 |
17 | expect(read(MEM_SIZE - 1)).toBe(0x9876)
^
error: expect(received).toBe(expected)
Expected: 39030
Received: NaN](https://cdn.bsky.app/img/feed_fullsize/plain/did:plc:ih3rt6r3sesh2flndp7oefwc/bafkreigsgtx6hbv6nvd3sct2mvujowo7l5lv35mzibgfhwuxz46mibm5by@jpeg)
kissa.bsky.social
@kissa.bsky.social
Tomfoolery, nincompoopery, programming
37 followers374 following39 posts