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// 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 last;
/** Initializes the class. */
function void init() {
let memory = 0;
let heap = 2048;
let heap[0] = -1;
let heap[1] = 14334;
let last = 0;
return;
}
/** 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;
return;
}
/** 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) {
do String.println("Insufficient space for allocation!");
do Sys.error(1);
return -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 oBase;
let oBase = o - heap - 2;
let heap[oBase] = -1;
let heap[last] = oBase;
let last = oBase;
return;
}
}
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