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=head1 NAME
Measure sizeof() of Perl's C Structures
=head1 Description
This document describes the I<sizeof> various structures, as
determined by I<util/sizeof.pl>. These measurements are mainly for
research purposes into making Perl things smaller, or rather, how to
use less Perl things.
=head1 Perl Structures
Structures diagrams are courtesy gdb (print pretty) and a bit of hand crafting.
=over 4
=item CV - 229 minimum, 254 minimum w/ symbol table entry
cv = {
sv_any = { // XPVCV *
xpv_pv = 0x0, // char *
xpv_cur = 0, // STRLEN
xpv_len = 0, // STRLEN
xof_off = 0 , // IV
xnv_nv = 0, // NV
xmg_magic = 0x0, // MAGIC *
xmg_stash = 0x0, // HV *
xcv_stash = 0x0, // HV *
xcv_start = 0x0, // OP *
xcv_root = 0x0, // OP *
xcv_xsub = 0x0, // void (*)(register PerlInterpreter *, CV *)
xcv_xsubany = { // ANY
any_ptr = 0x0,
any_i32 = 0,
any_iv = 0,
any_long = 0,
any_dptr = 0,
any_dxptr = 0
},
xcv_gv = { // GV *
sv_any = { // void *
xpv_pv = 0x0, // char *
xpv_cur = 0, // STRLEN
xpv_len = 0, // STRLEN
xiv_iv = 0, // IV
xnv_nv = 0, // NV
xmg_magic = { // MAGIC *
mg_moremagic = 0x0, // MAGIC *
mg_virtual = 0x0, // MGVTBL *
mg_private = 0, // U16
mg_type = 0, // char
mg_flags = 0, // U8
mg_obj = 0x0, // SV *
mg_ptr = 0x0, // char *
mg_len = 0, // I32
},
xmg_stash = 0x0, // HV *
xgv_gp = { // GP *
gp_sv = { // SV *
sv_any = 0x0, // void *
sv_refcnt = 0, // U32
sv_flags = 0 // U32
},
gp_refcnt = 0, // U32
gp_io = 0x0, // struct io *
gp_form = 0x0, // CV *
gp_av = 0x0, // AV *
gp_hv = 0x0, // HV *
gp_egv = 0x0, // GV *
gp_cv = 0x0, // CV *
gp_cvgen = 0, // U32
gp_flags = 0, // U32
gp_line = 0, // line_t
gp_file = 0x0, // char *
},
xgv_name = 0x0, // char *
xgv_namelen = 0, // STRLEN
xgv_stash = 0x0, // void *
xgv_flags = 0, // U8
},
sv_refcnt = 0, // U32
sv_flags = 0, // U32
},
xcv_file = 0x0, // char *
xcv_depth = 0, // long
xcv_padlist = 0x0, // AV *
xcv_outside = 0x0, // CV *
xcv_flags = 0, // cv_flags_t
}
sv_refcnt = 0, // U32
sv_flags = 0, // U32
};
In addition to the minimum bytes:
=over 4
=item name of the subroutine: GvNAMELEN(CvGV(cv))+1
=item symbol table entry: HvENTRY (25 + GvNAMELEN(CvGV(cv))+1)
=item minimum sizeof(AV) * 3: xcv_padlist if !CvXSUB(cv)
=item CvROOT(cv) optree
=back
=item HV - 60 minmum
hv = {
sv_any = { // SV *
xhv_array = 0x0, // char *
xhv_fill = 0, // STRLEN
xhv_max = 0, // STRLEN
xhv_keys = 0, // IV
xnv_nv = 0, // NV
xmg_magic = 0x0, // MAGIC *
xmg_stash = 0x0, // HV *
xhv_riter = 0, // I32
xhv_eiter = 0x0, // HE *
xhv_pmroot = 0x0, // PMOP *
xhv_name = 0x0 // char *
},
sv_refcnt = 0, // U32
sv_flags = 0, // U32
};
Each entry adds C<sizeof(HvENTRY)>, minimum of 7 (initial C<xhv_max>).
Note that keys of the same value share C<sizeof(HEK)>, across all
hashes.
=item HvENTRY - 25 + HeKLEN+1
sizeof(HE *) + sizeof(HE) + sizeof(HEK)
=item HE - 12
he = {
hent_next = 0x0, // HE *
hent_hek = 0x0, // HEK *
hent_val = 0x0 // SV *
};
=item HEK - 9 + hek_len
hek = {
hek_hash = 0, // U32
hek_len = 0, // I32
hek_key = 0, // char
};
=item AV - 53
av = {
sv_any = { // SV *
xav_array = 0x0, // char *
xav_fill = 0, // size_t
xav_max = 0, // size_t
xof_off = 0, // IV
xnv_nv = 0, // NV
xmg_magic = 0x0, // MAGIC *
xmg_stash = 0x0, // HV *
xav_alloc = 0x0, // SV **
xav_arylen = 0x0, // SV *
xav_flags = 0, // U8
},
sv_refcnt = 0, // U32
sv_flags = 0 // U32
};
In addition to the minimum bytes:
=over 4
=item AvFILL(av) * sizeof(SV *)
=back
=back
=head1 SEE ALSO
perlguts(3), B::Size(3),
http://gisle.aas.no/perl/illguts/
=head1 Maintainers
Maintainer is the person(s) you should contact with updates,
corrections and patches.
=over
=item *
Doug MacEachern E<lt>dougm (at) covalent.netE<gt>
=back
=head1 Authors
=over
=item *
Doug MacEachern E<lt>dougm (at) covalent.netE<gt>
=back
=cut
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