static I32
sortcv_xsub(pTHX_ SV *a, SV *b)
{
    dSP;
    I32 oldsaveix = PL_savestack_ix;
    I32 oldscopeix = PL_scopestack_ix;
    I32 result;
    CV *cv=(CV*)PL_sortcop;

    SP = PL_stack_base;
    PUSHMARK(SP);
    EXTEND(SP, 2);
    *++SP = a;
    *++SP = b;
    PUTBACK;
    (void)(*CvXSUB(cv))(aTHX_ cv);
    if (PL_stack_sp != PL_stack_base + 1)
    Perl_croak(aTHX_ "Sort subroutine didn't return single value");
    if (!SvNIOKp(*PL_stack_sp))
    Perl_croak(aTHX_ "Sort subroutine didn't return a numeric value");
    result = SvIV(*PL_stack_sp);
    while (PL_scopestack_ix > oldscopeix) {
    LEAVE;
    }
    leave_scope(oldsaveix);
    return result;
}

void
reduce(block,...)
    SV * block
PROTOTYPE: &@
CODE:
{
    SV *ret;
    int index;
    GV *agv,*bgv,*gv;
    HV *stash;
    CV *cv;
    OP *reducecop;
    PERL_CONTEXT *cx;
    SV** newsp;
    I32 gimme = G_SCALAR;
    U8 hasargs = 0;
    bool oldcatch = CATCH_GET;

    if(items <= 1) {
    XSRETURN_UNDEF;
    }
    agv = gv_fetchpv("a", TRUE, SVt_PV);
    bgv = gv_fetchpv("b", TRUE, SVt_PV);
    SAVESPTR(GvSV(agv));
    SAVESPTR(GvSV(bgv));
    cv = sv_2cv(block, &stash, &gv, 0);
    reducecop = CvSTART(cv);
    SAVESPTR(CvROOT(cv)->op_ppaddr);
    CvROOT(cv)->op_ppaddr = PL_ppaddr[OP_NULL];
#ifdef PAD_SET_CUR
    PAD_SET_CUR(CvPADLIST(cv),1);
#else
    SAVESPTR(PL_curpad);
    PL_curpad = AvARRAY((AV*)AvARRAY(CvPADLIST(cv))[1]);
#endif
    SAVETMPS;
    SAVESPTR(PL_op);
    ret = ST(1);
    CATCH_SET(TRUE);
    PUSHBLOCK(cx, CXt_SUB, SP);
    PUSHSUB(cx);
    if (!CvDEPTH(cv))
        (void)SvREFCNT_inc(cv);
    for(index = 2 ; index < items ; index++) {
    GvSV(agv) = ret;
    GvSV(bgv) = ST(index);
    PL_op = reducecop;
    CALLRUNOPS(aTHX);
    ret = *PL_stack_sp;
    }
    ST(0) = sv_mortalcopy(ret);
    POPBLOCK(cx,PL_curpm);
    CATCH_SET(oldcatch);
    XSRETURN(1);
}