Function cvSetSeqReaderPos

deps/opencv/modules/core/src/datastructs.cpp:1032–1121

Set reader position to given position, * either absolute or relative to the * current one: */

 *  current one:
 */
CV_IMPL void
cvSetSeqReaderPos( CvSeqReader* reader, int index, int is_relative )
{
    CvSeqBlock *block;
    int elem_size, count, total;

    if( !reader || !reader->seq )
        CV_Error( CV_StsNullPtr, "" );

    total = reader->seq->total;
    elem_size = reader->seq->elem_size;

    if( !is_relative )
    {
        if( index < 0 )
        {
            if( index < -total )
                CV_Error( CV_StsOutOfRange, "" );
            index += total;
        }
        else if( index >= total )
        {
            index -= total;
            if( index >= total )
                CV_Error( CV_StsOutOfRange, "" );
        }

        block = reader->seq->first;
        if( index >= (count = block->count) )
        {
            if( index + index <= total )
            {
                do
                {
                    block = block->next;
                    index -= count;
                }
                while( index >= (count = block->count) );
            }
            else
            {
                do
                {
                    block = block->prev;
                    total -= block->count;
                }
                while( index < total );
                index -= total;
            }
        }
        reader->ptr = block->data + index * elem_size;
        if( reader->block != block )
        {
            reader->block = block;
            reader->block_min = block->data;
            reader->block_max = block->data + block->count * elem_size;
        }
    }