reversepagenavigation.php

См. документацию.

<?php
namespace Bitrix\Main\UI;
 
class ReversePageNavigation extends PageNavigation
{
    public function __construct($id, $count)
    {
        parent::__construct($id);
        $this->setRecordCount($count);
    }

    public function getPageCount()
    {
        if($this->allRecords)
        {
            return 1;
        }
        $maxPages = (int)floor($this->recordCount/$this->pageSize);
        if($this->recordCount > 0 && $maxPages == 0)
        {
            $maxPages = 1;
        }
        return $maxPages;
    }

    public function getCurrentPage()
    {
        if($this->currentPage !== null)
        {
            return $this->currentPage;
        }
        return $this->getPageCount();
    }

    public function getOffset()
    {
        if($this->allRecords)
        {
            return 0;
        }
 
        $offset = 0;
        $pageCount = $this->getPageCount();
        $currentPage = $this->getCurrentPage();
 
        if($currentPage <> $pageCount)
        {
            //counting the last page (wich is the first one on reverse paging)
            $offset += ($this->recordCount % $this->pageSize);
        }
 
        $offset += ($pageCount - $currentPage) * $this->pageSize;
 
        return $offset;
    }

    public function getLimit()
    {
        if($this->allRecords)
        {
            return $this->getRecordCount();
        }
        if($this->getCurrentPage() == $this->getPageCount())
        {
            //the last page (displayed first)
            return $this->pageSize + ($this->recordCount % $this->pageSize);
        }
        else
        {
            return $this->pageSize;
        }
    }
}