assemblyscript/std/assembly/memory/arena.ts

// An simple arena allocator that provides a `clear_memory` function to reset
// everything to the initial state. A user must have to make sure that there
// a no more references to cleared memory.

const ALIGN_LOG2: usize = 3;
const ALIGN_SIZE: usize = 1 << ALIGN_LOG2;
const ALIGN_MASK: usize = ALIGN_SIZE - 1;

var HEAP_OFFSET: usize = HEAP_BASE; // generated by the compiler

export function allocate_memory(size: usize): usize {
  if (!size) return 0;
  var len: i32 = current_memory();
  if (HEAP_OFFSET + size > <usize>len << 16)
    if(grow_memory(max<i32>(<i32>ceil<f64>(<f64>size / 65536), len * 2 - len)) < 0)
      unreachable();
  var ptr: usize = HEAP_OFFSET;
  if ((HEAP_OFFSET += size) & ALIGN_MASK) // align next offset
    HEAP_OFFSET = (HEAP_OFFSET | ALIGN_MASK) + 1;
  set_memory(ptr, 0, size);
  return ptr;
}

export function free_memory(ptr: usize): void {
  // nop
}

export function clear_memory(): void {
  HEAP_OFFSET = HEAP_BASE;
}