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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
/**
* Memory operations library.
*/
class Memory {
static int MEMORY, HEAP_BASE, NEXT_POINTER, SIZE, HEAP_LIMIT, OOM, freeList, i;
/** Initializes memory parameters. */
function void init() {
let MEMORY = 0;
let SIZE = 0;
let NEXT_POINTER = 1;
let HEAP_BASE = 2048;
let HEAP_LIMIT = 16383;
let freeList = HEAP_BASE;
let freeList[SIZE] = HEAP_LIMIT - HEAP_BASE;
let OOM = 137;
let i = 0;
return;
}
/** Returns the value of the main memory at the given address. */
function int peek(int address) {
return MEMORY[address];
}
/** Sets the value of the main memory at this address
* to the given value. */
function void poke(int address, int value) {
let MEMORY[address] = value;
return;
}
/** finds and allocates from the heap a memory block of the
* specified size and returns a reference to its base address. */
function int alloc(int size) {
var bool defragged;
var int currentFreeSegment, block, newFreeSegment, previousFreeSegment;
let defragged = false;
let currentFreeSegment = freeList;
while (~block) {
if (currentFreeSegment[SIZE] > size) {
if (currentFreeSegment = freeList) {
if (currentFreeSegment[NEXT_POINTER]) {
let freeList = currentFreeSegment[NEXT_POINTER];
} else {
let freeList = currentFreeSegment + size + 1;
let freeList[SIZE] = currentFreeSegment[SIZE] - size - 1;
}
} else {
if (size < (currentFreeSegment[SIZE] - 2)) {
let newFreeSegment = currentFreeSegment + size + 1;
let newFreeSegment[SIZE] = currentFreeSegment[SIZE] - size - 1;
let previousFreeSegment[NEXT_POINTER] = newFreeSegment;
} else {
let previousFreeSegment[NEXT_POINTER] = currentFreeSegment[NEXT_POINTER];
}
}
let block = currentFreeSegment + 1;
} else {
if (currentFreeSegment[NEXT_POINTER] = null) {
if (defragged) {
do Sys.error(OOM);
} else {
do Memory.defrag();
let defragged = true;
let currentFreeSegment = freeList;
}
} else {
let previousFreeSegment = currentFreeSegment;
let currentFreeSegment = currentFreeSegment[NEXT_POINTER];
}
}
}
let block[-1] = size + 1;
let block[0] = null;
return block;
}
function void defrag() {
var int currentFreeSegment, nextFreeSegment;
let currentFreeSegment = freeList;
let nextFreeSegment = currentFreeSegment[NEXT_POINTER];
while (~(nextFreeSegment = 0)) {
if ((currentFreeSegment + currentFreeSegment[SIZE]) = nextFreeSegment) {
let currentFreeSegment[SIZE] = currentFreeSegment[SIZE] + nextFreeSegment[SIZE];
let currentFreeSegment[NEXT_POINTER] = nextFreeSegment[NEXT_POINTER];
let nextFreeSegment[SIZE] = null;
let nextFreeSegment[NEXT_POINTER] = null;
}
let currentFreeSegment = nextFreeSegment;
let nextFreeSegment = currentFreeSegment[NEXT_POINTER];
}
return;
}
/** De-allocates the given object and frees its space. */
function void deAlloc(int block) {
var int segment, segmentLength, oldFreeList, currentFreeSegment, oldNextSegment;
let segment = block - 1;
let segmentLength = segment[0];
while (i < (segmentLength - 1)) {
let block[i] = null;
let i = i + 1;
}
if (segment < freeList) {
let oldFreeList = freeList;
let freeList = segment;
let freeList[NEXT_POINTER] = oldFreeList;
return;
}
let currentFreeSegment = freeList;
while ((currentFreeSegment[NEXT_POINTER] < segment) & currentFreeSegment[NEXT_POINTER]) {
let currentFreeSegment = currentFreeSegment[NEXT_POINTER];
}
if (currentFreeSegment[NEXT_POINTER] > 0) {
let oldNextSegment = currentFreeSegment[NEXT_POINTER];
let currentFreeSegment[NEXT_POINTER] = segment;
let segment[NEXT_POINTER] = oldNextSegment;
} else {
let currentFreeSegment[NEXT_POINTER] = segment;
}
return;
}
}
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