Re^2: XS Prepending space to an SVs PV

modified to accept an additional argument that indicates how much extra space should be allocated when reallocation of the string memory is required:

static char *
my_sv_unchop(pTHX_ SV *sv, STRLEN size, STRLEN reserve) {
    STRLEN len;
    char *pv = SvPV(sv, len);
    IV off = SvOOK(sv) ? SvIVX(sv) : 0;
    if (!size)
        return pv;
 
    if (off >= size) {
        SvLEN_set(sv, SvLEN(sv) + size);
        SvCUR_set(sv, len + size);
        SvPV_set(sv, pv - size);
        if (off == size)
            SvFLAGS(sv) &= ~SVf_OOK;
        else
            SvIV_set(sv, off - size);
    }
    else {
        size += reserve;
        if ((size < reserve) || (len + size < size))
            Perl_croak(aTHX_ "panic: memory wrap");
        
        if (len + size <= off + SvLEN(sv)) {
            SvCUR_set(sv, len + size);
            SvPV_set(sv, pv - off);
            Move(pv, pv + size - off, len, char);
            if (off) {
                SvLEN_set(sv, SvLEN(sv) + off );
                SvFLAGS(sv) &= ~SVf_OOK;
            }
        }
        else {
            SV *tmp = sv_2mortal(newSV(len + size));
            char *tmp_pv;
            SvPOK_on(tmp);
            tmp_pv = SvPV_nolen(tmp);
            Move(pv, tmp_pv + size, len, char);
            SvCUR_set(tmp, len + size);
            sv_setsv(sv, tmp);
        }
 
        if (reserve)
            sv_chop(sv, SvPVX(sv) + reserve);
    }
    return SvPVX(sv);
}
[download]

Comment on Re^2: XS Prepending space to an SVs PV Download Code

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Re^3: XS Prepending space to an SVs PV by BrowserUk (Patriarch) on Apr 27, 2006 at 01:58 UTC
Many thanks (again) for this code, it is very generous of you and so much easier to learn from than the pure reference material of the 'guts and 'api docs. I set about adapting the above sub to my needs which are slightly less demanding that yours. The naming of `sv_chop` is (historical; set in stone; not of your making), slightly confusing with respect to Perl's chop as they operate on different ends of the string. That makes `sv_unchop` even more confusing :) Anyway, whilst reading the docs on `sv_chop`, I noticed `sv_insert` and relating that back to creamygoodness' explanation and demonstration that used substr to prepend to a string, I thought I'd see if I could use that to simplify things a little. What I came up with is this: `if( *a == 9 ) { ## Time to prepend another byte if( SvOOK( n ) ) { ## If we've some reserve left use it SvLEN_set( n, SvLEN( n ) +1 ); SvCUR_set( n, ++l ); SvPV_set( n, --a ); } else { ## else insert 100 more bytes and use sv_chop ## to reserve 99 of them for later char pad[100] = { 0, }; ## Initialise the reserve to all z +eros sv_insert( n, 0, 0, pad, 100 ); sv_chop( n, SvPVX( n ) + 99 ); a = SvPVX( n ); ++l; } } ...` [download] Whether that could be useful to you I don't know, but if you have the time to cast an eye over it and tell me if you see any obvious fopars... thanks again. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^4: XS Prepending space to an SVs PV by salva (Canon) on Apr 27, 2006 at 08:48 UTC
You have to check that there is still space free when the OOK flag is true and update the IV also: `... if (SvOOK( n ) && (SvIV(sv) > 0)) { /* If we've some reserve left use +it */ SvLEN_set( n, SvLEN( n ) +1 ); SvCUR_set( n, ++l ); SvPV_set( n, --a ); SvIVX(sv)--; } ...` [download]	[reply] [d/l]