/*
 * Copyright 2019 Google LLC. All Rights Reserved. This file and proprietary
 * source code may only be used and distributed under the Widevine Master
 * License Agreement.
 */

#include "bump_allocator.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define INITIAL_ALLOCATOR_BUFFER_SIZE (8 * 1024)

static uint8_t buffer[INITIAL_ALLOCATOR_BUFFER_SIZE];
static uint8_t* ptr = buffer;
static size_t buffer_size = sizeof(buffer);
static size_t buffer_offset = 0;

uint8_t* BumpAllocate(size_t nbytes) {
  size_t new_offset = 0;
  if(__builtin_add_overflow(buffer_offset, nbytes, &new_offset) ||
     (new_offset > buffer_size)) {
    /*
     * The bump allocator buffer should be large enough that a malloc
     * is never required. But allow a malloc if the buffer overflows.
     */
    fprintf(stderr, "Warning: bump allocator memory size exceeded,"
            " size=%zd, requested=%zd\n", buffer_size, new_offset);
    size_t new_size = 2 * buffer_size;
    uint8_t* new_ptr = malloc(new_size);
    if (new_ptr == NULL) {
      fprintf(stderr, "Fatal: bump allocator could not malloc %zd bytes\n",
              new_size);
      abort();
    }
    memcpy(new_ptr, ptr, buffer_size);
    memset(new_ptr + buffer_size, 0, buffer_size);
    buffer_size = new_size;
    if (ptr != buffer) {
      free(ptr);
    }
    ptr = new_ptr;
  }
  uint8_t* result = ptr + buffer_offset;
  memset(result, 0, nbytes);
  buffer_offset = new_offset;
  return result;
}

void BumpAllocator_Reset(void) {
  buffer_offset = 0;
  if (ptr != buffer) {
    free(ptr);
  }
  ptr = buffer;
  buffer_size = sizeof(buffer);
  memset(buffer, 0, sizeof(buffer));
}