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Postings from October 2000
So, I'm trying to describe what an PVIV is, and the way to do that is to
generate one. OK, so...
% ./perl -Ilib -MDevel::Peek -e '$a="12";$a+=1; Dump($a)'
SV = PVNV(0x80f3c98) at 0x80fcf30
REFCNT = 1
FLAGS = (NOK,pNOK)
IV = 0
NV = 13
PV = 0x8101b40 "12"\0
CUR = 2
LEN = 3
Argh. Hang on, I didn't do anything floating point. Why has it upgraded to
PVNV?
We have two addition ops: one for integers, (pp_i_add) and one for
non-integers. (pp_add) If "use integer" is in force, Perl can change
pp_add to pp_i_add at compile time, during the constant-folding stage.
Otherwise, at runtime, you have to go through pp_add which pops NVs off
the stack. This means that your SV gets upgraded to PVNV, possibly
needlessly.
Would it be an efficiency hack to say the moral equivalent of
if(SvIOK(left) && SvIOK(right))
pp_i_add();
and save the upgrade?
--
"I will make no bargains with terrorist hardware."
-- Peter da Silva
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