blob: b1e67ef73d4e91997c5c717897ea075a4ac38685 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
|
// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/12/Memory.jack
/**
* This library provides two services: direct access to the computer's main
* memory (RAM), and allocation and recycling of memory blocks. The Hack RAM
* consists of 32,768 words, each holding a 16-bit binary number.
*/
class Memory {
static Array memory;
static Array heap;
static int first;
/** Initializes the class. */
function void init() {
let memory = 0;
let heap = 2048;
let heap[0] = -1;
let heap[1] = 14334;
}
/** Returns the RAM value at the given address. */
function int peek(int address) {
return memory[address];
}
/** Sets the RAM value at the given address to the given value. */
function void poke(int address, int value) {
let memory[address] = value;
}
/** Finds an available RAM block of the given size and returns
* a reference to its base address. */
function int alloc(int size) {
var int current;
var int size2;
var int newLast;
let current = 0;
let size2 = size + 2;
while ((current > -1) & (heap[current + 1] < size2)) {
let current = heap[current];
}
if (current = -1) {
String.println("Insufficient space for allocation!");
Sys.error(1);
} else {
let heap[current + 1] = heap[current + 1] - size2;
let newLast = current + heap[current + 1] + 2;
let heap[newLast] = heap[current];
let heap[current] = newLast;
let heap[newLast + 1] = size;
return heap + newLast + 2;
}
}
/** De-allocates the given object (cast as an array) by making
* it available for future allocations. */
function void deAlloc(Array o) {
var int base;
var int current;
var int prev;
let prev = 0;
let current = heap[prev];
let oBase = o - heap - 2;
while ((current > -1) & (~(current = oBase))){
let prev = current;
let current = heap[current];
}
if (current = -1) {
String.println("The impossible happened");
Sys.error(1);
} else {
let heap[prev] = heap[current]
let heap[prev + 1] = heap[prev] - prev - 2;
return;
}
}
}
|
