poolGrow(STRING_POOL *pool) {
  if (pool->freeBlocks) {
    if (pool->start == 0) {
      pool->blocks = pool->freeBlocks;
      pool->freeBlocks = pool->freeBlocks->next;
      pool->blocks->next = NULL;
      pool->start = pool->blocks->s;
      pool->end = pool->start + pool->blocks->size;
      pool->ptr = pool->start;
      return XML_TRUE;
    }
    if (pool->end - pool->start < pool->freeBlocks->size) {
      BLOCK *tem = pool->freeBlocks->next;
      pool->freeBlocks->next = pool->blocks;
      pool->blocks = pool->freeBlocks;
      pool->freeBlocks = tem;
      memcpy(pool->blocks->s, pool->start,
             (pool->end - pool->start) * sizeof(XML_Char));
      pool->ptr = pool->blocks->s + (pool->ptr - pool->start);
      pool->start = pool->blocks->s;
      pool->end = pool->start + pool->blocks->size;
      return XML_TRUE;
    }
  }
  if (pool->blocks && pool->start == pool->blocks->s) {
    BLOCK *temp;
    int blockSize = (int)((unsigned)(pool->end - pool->start) * 2U);
    size_t bytesToAllocate;

    /* NOTE: Needs to be calculated prior to calling `realloc`
             to avoid dangling pointers: */
    const ptrdiff_t offsetInsideBlock = pool->ptr - pool->start;

    if (blockSize < 0) {
      /* This condition traps a situation where either more than
       * INT_MAX/2 bytes have already been allocated.  This isn't
       * readily testable, since it is unlikely that an average
       * machine will have that much memory, so we exclude it from the
       * coverage statistics.
       */
      return XML_FALSE; /* LCOV_EXCL_LINE */
    }

    bytesToAllocate = poolBytesToAllocateFor(blockSize);
    if (bytesToAllocate == 0)
      return XML_FALSE;

    temp = (BLOCK *)pool->mem->realloc_fcn(pool->blocks,
                                           (unsigned)bytesToAllocate);
    if (temp == NULL)
      return XML_FALSE;
    pool->blocks = temp;
    pool->blocks->size = blockSize;
    pool->ptr = pool->blocks->s + offsetInsideBlock;
    pool->start = pool->blocks->s;
    pool->end = pool->start + blockSize;
  } else {
    BLOCK *tem;
    int blockSize = (int)(pool->end - pool->start);
    size_t bytesToAllocate;

    if (blockSize < 0) {
      /* This condition traps a situation where either more than
       * INT_MAX bytes have already been allocated (which is prevented
       * by various pieces of program logic, not least this one, never
       * mind the unlikelihood of actually having that much memory) or
       * the pool control fields have been corrupted (which could
       * conceivably happen in an extremely buggy user handler
       * function).  Either way it isn't readily testable, so we
       * exclude it from the coverage statistics.
       */
      return XML_FALSE; /* LCOV_EXCL_LINE */
    }

    if (blockSize < INIT_BLOCK_SIZE)
      blockSize = INIT_BLOCK_SIZE;
    else {
      /* Detect overflow, avoiding _signed_ overflow undefined behavior */
      if ((int)((unsigned)blockSize * 2U) < 0) {
        return XML_FALSE;
      }
      blockSize *= 2;
    }

    bytesToAllocate = poolBytesToAllocateFor(blockSize);
    if (bytesToAllocate == 0)
      return XML_FALSE;

    tem = (BLOCK *)pool->mem->malloc_fcn(bytesToAllocate);
    if (! tem)
      return XML_FALSE;
    tem->size = blockSize;
    tem->next = pool->blocks;
    pool->blocks = tem;
    if (pool->ptr != pool->start)
      memcpy(tem->s, pool->start, (pool->ptr - pool->start) * sizeof(XML_Char));
    pool->ptr = tem->s + (pool->ptr - pool->start);
    pool->start = tem->s;
    pool->end = tem->s + blockSize;
  }
  return XML_TRUE;
}