... hv = (HV*)NEWSV(502,0); ...
... creates a new hash. We can see that the basic memory needed is 502 bytes
That's not correct: the first parameter to NEWSV is an identifier, used only for malloc debugging. It is the second parameter that provides the size, and a value of zero means "give me a new empty SV - I'll fill it in myself".
It is the following call to sv_upgrade((SV *)hv, SVt_PVHV) that actually turns this into something capable of storing a hash. In particular it allocates the struct xpvhv, defined in hv.h: struct xpvhv {
char * xhv_array; /* pointer to malloced string */
STRLEN xhv_fill; /* how full xhv_array currently is */
STRLEN xhv_max; /* subscript of last element of xhv_array */
IV xhv_keys; /* how many elements in the array */
NV xnv_nv; /* numeric value, if any */
#define xhv_placeholders xnv_nv
MAGIC* xmg_magic; /* magic for scalar array */
HV* xmg_stash; /* class package */
I32 xhv_riter; /* current root of iterator */
HE *xhv_eiter; /* current entry of iterator */
PMOP *xhv_pmroot; /* list of pm's for this package */
char *xhv_name; /* name, if a symbol table */
};
Also the number of buckets does increase in powers of 2, as shown by the example code in demerphq's response. S_more_he() is not relevant to this - it is (I think) fetching a new structure from a malloc arena. The routine you want is S_hsplit() which quite early on does a nice clear: register I32 newsize = oldsize * 2;
Hugo
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