cvCreateSeq源碼分析

CV_IMPL CvSeq *
cvCreateSeq( int seq_flags, int header_size, int elem_size, CvMemStorage * storage )
{
    CvSeq *seq = 0;

    CV_FUNCNAME( "cvCreateSeq" );

    __BEGIN__;

    if( !storage )
        CV_ERROR( CV_StsNullPtr, "" );
    if( header_size < (int)sizeof( CvSeq ) || elem_size <= 0 )              //序列頭大小不小於sizeof( CvSeq )
        CV_ERROR( CV_StsBadSize, "" );

    /* allocate sequence header */   分配序列頭
    CV_CALL( seq = (CvSeq*)cvMemStorageAlloc( storage, header_size ));   //在存儲塊中分配一內存緩衝區
    memset( seq, 0, header_size );           //初始化爲0

    seq->header_size = header_size;
    seq->flags = (seq_flags & ~CV_MAGIC_MASK) | CV_SEQ_MAGIC_VAL;
    {
        int elemtype = CV_MAT_TYPE(seq_flags);
        int typesize = CV_ELEM_SIZE(elemtype);

        if( elemtype != CV_SEQ_ELTYPE_GENERIC &&
            typesize != 0 && typesize != elem_size )
            CV_ERROR( CV_StsBadSize,
            "Specified element size doesn't match to the size of the specified element type "
            "(try to use 0 for element type)" );
    }
    seq->elem_size = elem_size;
    seq->storage = storage;

    CV_CALL( cvSetSeqBlockSize( seq, (1 << 10)/elem_size ));   //設置序列塊的大小;當序列緩衝區中空間消耗完時，函數爲 delta_elems 個序列元素分配空間。如果新分配

                                                                                                    //的空間與 之前分配的空間相鄰的話，這兩個塊就合併，否則，就創建了一個新的序列快。設置seq->delta_elems

    __END__;

    return seq;        //cvCreateSeq完成了對cvseq結構體 flags、header_size、elem_size、delta_elems的填充；
}

 

其中

CV_IMPL void*
cvMemStorageAlloc( CvMemStorage* storage, size_t size )
{
    char *ptr = 0;
   
    CV_FUNCNAME( "cvMemStorageAlloc" );

    __BEGIN__;

    if( !storage )
        CV_ERROR( CV_StsNullPtr, "NULL storage pointer" );

    if( size > INT_MAX )
        CV_ERROR( CV_StsOutOfRange, "Too large memory block is requested" );

    assert( storage->free_space % CV_STRUCT_ALIGN == 0 );

    if( (size_t)storage->free_space < size )
    {
        size_t max_free_space = cvAlignLeft(storage->block_size - sizeof(CvMemBlock), CV_STRUCT_ALIGN);
        if( max_free_space < size )
            CV_ERROR( CV_StsOutOfRange, "requested size is negative or too big" );

        CV_CALL( icvGoNextMemBlock( storage ));
    }

    ptr = ICV_FREE_PTR(storage);
    assert( (size_t)ptr % CV_STRUCT_ALIGN == 0 );
    storage->free_space = cvAlignLeft(storage->free_space - (int)size, CV_STRUCT_ALIGN );

    __END__;

    return ptr;
}