#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

#include <string.h>

// a compiler supporting C99 is required

/* try to be compatible with older perls */
/* SvPV_nolen() macro first defined in 5.005_55 */
/* this is slow, not threadsafe, but works */
#include "patchlevel.h"
#if (PATCHLEVEL == 4) || ((PATCHLEVEL == 5) && (SUBVERSION < 55))
static STRLEN nolen_na;
# define SvPV_nolen(sv) SvPV ((sv), nolen_na)
#endif
#if PATCHLEVEL < 6
# define call_sv perl_call_sv
#endif

#define KEYLEN 8	// number of bytes in the l, m, r fields

static SV *
new_key (void)
{
  SV *new = NEWSV(0, KEYLEN);
  SvPOK_only (new);
  SvCUR_set (new, KEYLEN);

  return new;
}

MODULE = XML::DB   PACKAGE = XML::DB::Key

PROTOTYPES: ENABLE

int
KEYLEN()
	CODE:
        RETVAL = KEYLEN;
	OUTPUT:
        RETVAL

SV *
0()
	ALIAS:
           1 = 255
	CODE:
        RETVAL = new_key ();
        memset (SvPVX (RETVAL), ix, KEYLEN);
	OUTPUT:
        RETVAL

# calculcate l + r
SV *
m(ls,rs)
	SV *	ls
        SV *	rs
        CODE:
        unsigned char *l, *m, *r, *me;
        unsigned int mx, carry;

        RETVAL = new_key ();

        l =       SvPVX (ls    )  + KEYLEN;
        r =       SvPVX (rs    )  + KEYLEN;
        m = (me = SvPVX (RETVAL)) + KEYLEN;

        me [0] = 'U';
        me [1] = 'U';

        mx = (unsigned int)*--l + (unsigned int)*--r + 1; *--m = (mx & 0x0ff) >> 1;
        carry = mx & 0x100;

        do
          {
            mx = (unsigned int)*--l + (unsigned int)*--r + (carry >> 8); *--m = (mx & 0x0ff) >> 1;

            m[1] |= (mx & 0x001) << 7;
            carry = (mx & 0x100);
          }
        while (me < m);

        m[0] |= carry >> 1;

        OUTPUT:
        RETVAL