what 's meanning of the marco `DK_ENTRIES` in cpython code dictobject.c

Question

I read the code of dictobject.c , can not figure out this

#define DK_ENTRIES(dk) \
    ((PyDictKeyEntry*)(&((int8_t*)((dk)->dk_indices))[DK_SIZE(dk) * DK_IXSIZE(dk)]))

any one can explain this macro ,hep me to read this macro and what this for ?

Answer 1

After some struggle，I find something below：

First dk is PyDictKeysObject:

typedef struct _dictkeysobject PyDictKeysObject;
struct _dictkeysobject {
    Py_ssize_t dk_refcnt;
    Py_ssize_t dk_size;
    dict_lookup_func dk_lookup;
    Py_ssize_t dk_usable;
    Py_ssize_t dk_nentries;
    char dk_indices[];
};

note the last elementdk_indices , flexible array member

simply,

DK_SIZE is the dk_size in struct;

DK_IXSIZE can be 1 or 2 or 4 or 8

((int8_t*)((dk)->dk_indices))[DK_SIZE(dk) * DK_IXSIZE(dk)]

is a pointer with n(dk_size*1?) offset

and the end return a pointer to PyDictKeyEntry

Finally, This macro return a PyDictKeyEntry, which have n(dk_size*1?) offset with dk->dk_indices