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ambient.c

#ifndef lint
static const char RCSid[] = "$Id: ambient.c,v 2.67 2007/11/17 06:21:58 greg Exp $";
#endif
/*
 *  ambient.c - routines dealing with ambient (inter-reflected) component.
 *
 *  Declarations of external symbols in ambient.h
 */

#include "copyright.h"

#include <string.h>

#include  "platform.h"
#include  "ray.h"
#include  "otypes.h"
#include  "resolu.h"
#include  "ambient.h"
#include  "random.h"

#ifndef  OCTSCALE
#define      OCTSCALE   1.0   /* ceil((valid rad.)/(cube size)) */
#endif

extern char  *shm_boundary;   /* memory sharing boundary */

#ifndef  MAXASET
#define      MAXASET    4095  /* maximum number of elements in ambient set */
#endif
OBJECT      ambset[MAXASET+1]={0};  /* ambient include/exclude set */

double      maxarad;          /* maximum ambient radius */
double      minarad;          /* minimum ambient radius */

static AMBTREE    atrunk;           /* our ambient trunk node */

static FILE  *ambfp = NULL;   /* ambient file pointer */
static int  nunflshed = 0;    /* number of unflushed ambient values */

#ifndef SORT_THRESH
#ifdef SMLMEM
#define SORT_THRESH     ((3L<<20)/sizeof(AMBVAL))
#else
#define SORT_THRESH     ((9L<<20)/sizeof(AMBVAL))
#endif
#endif
#ifndef SORT_INTVL
#define SORT_INTVL      (SORT_THRESH<<1)
#endif
#ifndef MAX_SORT_INTVL
#define MAX_SORT_INTVL  (SORT_INTVL<<6)
#endif

static double  avsum = 0.;          /* computed ambient value sum (log) */
static unsigned int  navsum = 0;    /* number of values in avsum */
static unsigned int  nambvals = 0;  /* total number of indirect values */
static unsigned int  nambshare = 0; /* number of values from file */
static unsigned long  ambclock = 0; /* ambient access clock */
static unsigned long  lastsort = 0; /* time of last value sort */
static long  sortintvl = SORT_INTVL;      /* time until next sort */
static FILE  *ambinp = NULL;        /* auxiliary file for input */
static long  lastpos = -1;          /* last flush position */

#define MAXACLOCK (1L<<30)    /* clock turnover value */
      /*
       * Track access times unless we are sharing ambient values
       * through memory on a multiprocessor, when we want to avoid
       * claiming our own memory (copy on write).  Go ahead anyway
       * if more than two thirds of our values are unshared.
       * Compile with -Dtracktime=0 to turn this code off.
       */
#ifndef tracktime
#define tracktime (shm_boundary == NULL || nambvals > 3*nambshare)
#endif

#define      AMBFLUSH   (BUFSIZ/AMBVALSIZ)

#define      newambval()      (AMBVAL *)malloc(sizeof(AMBVAL))
#define  freeav(av)     free((void *)av);

static void initambfile(int creat);
static void avsave(AMBVAL *av);
static AMBVAL *avstore(AMBVAL  *aval);
static AMBTREE *newambtree(void);
static void freeambtree(AMBTREE  *atp);

typedef void unloadtf_t(void *);
static unloadtf_t avinsert;
static unloadtf_t av2list;
static void unloadatree(AMBTREE  *at, unloadtf_t *f);

static int aposcmp(const void *avp1, const void *avp2);
static int avlmemi(AMBVAL *avaddr);
static void sortambvals(int always);

#ifdef  F_SETLKW
static void aflock(int  typ);
#endif


extern void
setambres(                    /* set ambient resolution */
      int  ar
)
{
      ambres = ar < 0 ? 0 : ar;           /* may be done already */
                                    /* set min & max radii */
      if (ar <= 0) {
            minarad = 0;
            maxarad = thescene.cusize / 2.0;
      } else {
            minarad = thescene.cusize / ar;
            maxarad = 64 * minarad;             /* heuristic */
            if (maxarad > thescene.cusize / 2.0)
                  maxarad = thescene.cusize / 2.0;
      }
      if (minarad <= FTINY)
            minarad = 10*FTINY;
      if (maxarad <= minarad)
            maxarad = 64 * minarad;
}


extern void
setambacc(                    /* set ambient accuracy */
      double  newa
)
{
      double  ambdiff;

      if (newa < 0.0)
            newa = 0.0;
      ambdiff = fabs(newa - ambacc);
      if (ambdiff >= .01 && (ambacc = newa) > FTINY && nambvals > 0)
            sortambvals(1);               /* rebuild tree */
}


extern void
setambient(void)                    /* initialize calculation */
{
      int   readonly = 0;
      long  flen;
      AMBVAL      amb;
                                    /* make sure we're fresh */
      ambdone();
                                    /* init ambient limits */
      setambres(ambres);
      setambacc(ambacc);
      if (ambfile == NULL || !ambfile[0])
            return;
      if (ambacc <= FTINY) {
            sprintf(errmsg, "zero ambient accuracy so \"%s\" not opened",
                        ambfile);
            error(WARNING, errmsg);
            return;
      }
                                    /* open ambient file */
      if ((ambfp = fopen(ambfile, "r+")) == NULL)
            readonly = (ambfp = fopen(ambfile, "r")) != NULL;
      if (ambfp != NULL) {
            initambfile(0);               /* file exists */
            lastpos = ftell(ambfp);
            while (readambval(&amb, ambfp))
                  avinsert(avstore(&amb));
            nambshare = nambvals;         /* share loaded values */
            if (readonly) {
                  sprintf(errmsg,
                        "loaded %u values from read-only ambient file",
                              nambvals);
                  error(WARNING, errmsg);
                  fclose(ambfp);          /* close file so no writes */
                  ambfp = NULL;
                  return;                 /* avoid ambsync() */
            }
                                    /* align file pointer */
            lastpos += (long)nambvals*AMBVALSIZ;
            flen = lseek(fileno(ambfp), (off_t)0, SEEK_END);
            if (flen != lastpos) {
                  sprintf(errmsg,
                  "ignoring last %ld values in ambient file (corrupted)",
                              (flen - lastpos)/AMBVALSIZ);
                  error(WARNING, errmsg);
                  fseek(ambfp, lastpos, SEEK_SET);
#ifndef _WIN32 /* XXX we need a replacement for that one */
                  ftruncate(fileno(ambfp), (off_t)lastpos);
#endif
            }
      } else if ((ambfp = fopen(ambfile, "w+")) != NULL) {
            initambfile(1);               /* else create new file */
            lastpos = ftell(ambfp);
      } else {
            sprintf(errmsg, "cannot open ambient file \"%s\"", ambfile);
            error(SYSTEM, errmsg);
      }
      ambsync();              /* load previous values */
}


extern void
ambdone(void)                 /* close ambient file and free memory */
{
      if (ambfp != NULL) {          /* close ambient file */
            ambsync();
            fclose(ambfp);
            ambfp = NULL;
            if (ambinp != NULL) {   
                  fclose(ambinp);
                  ambinp = NULL;
            }
            lastpos = -1;
      }
                              /* free ambient tree */
      unloadatree(&atrunk, free);
                              /* reset state variables */
      avsum = 0.;
      navsum = 0;
      nambvals = 0;
      nambshare = 0;
      ambclock = 0;
      lastsort = 0;
      sortintvl = SORT_INTVL;
}


extern void
ambnotify(              /* record new modifier */
      OBJECT      obj
)
{
      static int  hitlimit = 0;
      register OBJREC    *o;
      register char  **amblp;

      if (obj == OVOID) {           /* starting over */
            ambset[0] = 0;
            hitlimit = 0;
            return;
      }
      o = objptr(obj);
      if (hitlimit || !ismodifier(o->otype))
            return;
      for (amblp = amblist; *amblp != NULL; amblp++)
            if (!strcmp(o->oname, *amblp)) {
                  if (ambset[0] >= MAXASET) {
                        error(WARNING, "too many modifiers in ambient list");
                        hitlimit++;
                        return;           /* should this be fatal? */
                  }
                  insertelem(ambset, obj);
                  return;
            }
}


extern void
multambient(            /* compute ambient component & multiply by coef. */
      COLOR  aval,
      register RAY  *r,
      FVECT  nrm
)
{
      static int  rdepth = 0;             /* ambient recursion */
      COLOR acol;
      double      d, l;

      if (ambdiv <= 0)              /* no ambient calculation */
            goto dumbamb;
                                    /* check number of bounces */
      if (rdepth >= ambounce)
            goto dumbamb;
                                    /* check ambient list */
      if (ambincl != -1 && r->ro != NULL &&
                  ambincl != inset(ambset, r->ro->omod))
            goto dumbamb;

      if (ambacc <= FTINY) {              /* no ambient storage */
            copycolor(acol, aval);
            rdepth++;
            d = doambient(acol, r, r->rweight, NULL, NULL);
            rdepth--;
            if (d <= FTINY)
                  goto dumbamb;
            copycolor(aval, acol);
            return;
      }

      if (tracktime)                      /* sort to minimize thrashing */
            sortambvals(0);
                                    /* interpolate ambient value */
      setcolor(acol, 0.0, 0.0, 0.0);
      d = sumambient(acol, r, nrm, rdepth,
                  &atrunk, thescene.cuorg, thescene.cusize);
      if (d > FTINY) {
            d = 1.0/d;
            scalecolor(acol, d);
            multcolor(aval, acol);
            return;
      }
      rdepth++;                     /* need to cache new value */
      d = makeambient(acol, r, nrm, rdepth-1);
      rdepth--;
      if (d > FTINY) {
            multcolor(aval, acol);        /* got new value */
            return;
      }
dumbamb:                            /* return global value */
      if ((ambvwt <= 0) | (navsum == 0)) {
            multcolor(aval, ambval);
            return;
      }
      l = bright(ambval);                 /* average in computations */
      if (l > FTINY) {
            d = (log(l)*(double)ambvwt + avsum) /
                        (double)(ambvwt + navsum);
            d = exp(d) / l;
            scalecolor(aval, d);
            multcolor(aval, ambval);      /* apply color of ambval */
      } else {
            d = exp( avsum / (double)navsum );
            scalecolor(aval, d);          /* neutral color */
      }
}


extern double
sumambient( /* get interpolated ambient value */
      COLOR  acol,
      register RAY  *r,
      FVECT  rn,
      int  al,
      AMBTREE      *at,
      FVECT  c0,
      double      s
)
{
      double      d, e1, e2, wt, wsum;
      COLOR  ct;
      FVECT  ck0;
      int  i;
      register int  j;
      register AMBVAL    *av;

      wsum = 0.0;
                              /* do this node */
      for (av = at->alist; av != NULL; av = av->next) {
            double      rn_dot = -2.0;
            if (tracktime)
                  av->latick = ambclock;
            /*
             *  Ambient level test.
             */
            if (av->lvl > al) /* list sorted, so this works */
                  break;
            if (av->weight < 0.9*r->rweight)
                  continue;
            /*
             *  Ambient radius test.
             */
            d = av->pos[0] - r->rop[0];
            e1 = d * d;
            d = av->pos[1] - r->rop[1];
            e1 += d * d;
            d = av->pos[2] - r->rop[2];
            e1 += d * d;
            e1 /= av->rad * av->rad;
            if (e1 > ambacc*ambacc*1.21)
                  continue;
            /*
             *  Direction test using closest normal.
             */
            d = DOT(av->dir, r->ron);
            if (rn != r->ron) {
                  rn_dot = DOT(av->dir, rn);
                  if (rn_dot > 1.0-FTINY)
                        rn_dot = 1.0-FTINY;
                  if (rn_dot >= d-FTINY) {
                        d = rn_dot;
                        rn_dot = -2.0;
                  }
            }
            e2 = (1.0 - d) * r->rweight;
            if (e2 < 0.0) e2 = 0.0;
            if (e1 + e2 > ambacc*ambacc*1.21)
                  continue;
            /*
             *  Ray behind test.
             */
            d = 0.0;
            for (j = 0; j < 3; j++)
                  d += (r->rop[j] - av->pos[j]) *
                              (av->dir[j] + r->ron[j]);
            if (d*0.5 < -minarad*ambacc-.001)
                  continue;
            /*
             *  Jittering final test reduces image artifacts.
             */
            e1 = sqrt(e1);
            e2 = sqrt(e2);
            wt = e1 + e2;
            if (wt > ambacc*(.9+.2*urand(9015+samplendx)))
                  continue;
            /*
             *  Recompute directional error using perturbed normal
             */
            if (rn_dot > 0.0) {
                  e2 = sqrt((1.0 - rn_dot)*r->rweight);
                  wt = e1 + e2;
            }
            if (wt <= 1e-3)
                  wt = 1e3;
            else
                  wt = 1.0 / wt;
            wsum += wt;
            extambient(ct, av, r->rop, rn);
            scalecolor(ct, wt);
            addcolor(acol, ct);
      }
      if (at->kid == NULL)
            return(wsum);
                              /* do children */
      s *= 0.5;
      for (i = 0; i < 8; i++) {
            for (j = 0; j < 3; j++) {
                  ck0[j] = c0[j];
                  if (1<<j & i)
                        ck0[j] += s;
                  if (r->rop[j] < ck0[j] - OCTSCALE*s)
                        break;
                  if (r->rop[j] > ck0[j] + (1.0+OCTSCALE)*s)
                        break;
            }
            if (j == 3)
                  wsum += sumambient(acol, r, rn, al,
                                    at->kid+i, ck0, s);
      }
      return(wsum);
}


extern double
makeambient(            /* make a new ambient value for storage */
      COLOR  acol,
      RAY  *r,
      FVECT  rn,
      int  al
)
{
      AMBVAL      amb;
      FVECT gp, gd;
      int   i;

      amb.weight = 1.0;             /* compute weight */
      for (i = al; i-- > 0; )
            amb.weight *= AVGREFL;
      if (r->rweight < 0.1*amb.weight)    /* heuristic override */
            amb.weight = 1.25*r->rweight;
      setcolor(acol, AVGREFL, AVGREFL, AVGREFL);
                                    /* compute ambient */
      amb.rad = doambient(acol, r, amb.weight, gp, gd);
      if (amb.rad <= FTINY) {
            setcolor(acol, 0.0, 0.0, 0.0);
            return(0.0);
      }
      scalecolor(acol, 1./AVGREFL);       /* undo assumed reflectance */
                                    /* store value */
      VCOPY(amb.pos, r->rop);
      VCOPY(amb.dir, r->ron);
      amb.lvl = al;
      copycolor(amb.val, acol);
      VCOPY(amb.gpos, gp);
      VCOPY(amb.gdir, gd);
                                    /* insert into tree */
      avsave(&amb);                       /* and save to file */
      if (rn != r->ron)
            extambient(acol, &amb, r->rop, rn); /* texture */
      return(amb.rad);
}


extern void
extambient(       /* extrapolate value at pv, nv */
      COLOR  cr,
      register AMBVAL    *ap,
      FVECT  pv,
      FVECT  nv
)
{
      FVECT  v1;
      register int  i;
      double      d;

      d = 1.0;                /* zeroeth order */
                              /* gradient due to translation */
      for (i = 0; i < 3; i++)
            d += ap->gpos[i]*(pv[i]-ap->pos[i]);
                              /* gradient due to rotation */
      VCROSS(v1, ap->dir, nv);
      d += DOT(ap->gdir, v1);
      if (d <= 0.0) {
            setcolor(cr, 0.0, 0.0, 0.0);
            return;
      }
      copycolor(cr, ap->val);
      scalecolor(cr, d);
}


static void
initambfile(            /* initialize ambient file */
      int  creat
)
{
      extern char  *progname, *octname;
      static char  *mybuf = NULL;

#ifdef      F_SETLKW
      aflock(creat ? F_WRLCK : F_RDLCK);
#endif
      SET_FILE_BINARY(ambfp);
      if (mybuf == NULL)
            mybuf = (char *)bmalloc(BUFSIZ+8);
      setbuf(ambfp, mybuf);
      if (creat) {                  /* new file */
            newheader("RADIANCE", ambfp);
            fprintf(ambfp, "%s -av %g %g %g -aw %d -ab %d -aa %g ",
                        progname, colval(ambval,RED),
                        colval(ambval,GRN), colval(ambval,BLU),
                        ambvwt, ambounce, ambacc);
            fprintf(ambfp, "-ad %d -as %d -ar %d ",
                        ambdiv, ambssamp, ambres);
            if (octname != NULL)
                  printargs(1, &octname, ambfp);
            else
                  fputc('\n', ambfp);
            fprintf(ambfp, "SOFTWARE= %s\n", VersionID);
            fputnow(ambfp);
            fputformat(AMBFMT, ambfp);
            putc('\n', ambfp);
            putambmagic(ambfp);
      } else if (checkheader(ambfp, AMBFMT, NULL) < 0 || !hasambmagic(ambfp))
            error(USER, "bad ambient file");
}


static void
avsave(                       /* insert and save an ambient value */
      AMBVAL      *av
)
{
      avinsert(avstore(av));
      if (ambfp == NULL)
            return;
      if (writambval(av, ambfp) < 0)
            goto writerr;
      if (++nunflshed >= AMBFLUSH)
            if (ambsync() == EOF)
                  goto writerr;
      return;
writerr:
      error(SYSTEM, "error writing to ambient file");
}


static AMBVAL *
avstore(                      /* allocate memory and store aval */
      register AMBVAL  *aval
)
{
      register AMBVAL  *av;
      double      d;

      if ((av = newambval()) == NULL)
            error(SYSTEM, "out of memory in avstore");
      *av = *aval;
      av->latick = ambclock;
      av->next = NULL;
      nambvals++;
      d = bright(av->val);
      if (d > FTINY) {        /* add to log sum for averaging */
            avsum += log(d);
            navsum++;
      }
      return(av);
}


#define ATALLOCSZ 512         /* #/8 trees to allocate at once */

static AMBTREE  *atfreelist = NULL; /* free ambient tree structures */


static AMBTREE *
newambtree(void)                    /* allocate 8 ambient tree structs */
{
      register AMBTREE  *atp, *upperlim;

      if (atfreelist == NULL) {     /* get more nodes */
            atfreelist = (AMBTREE *)malloc(ATALLOCSZ*8*sizeof(AMBTREE));
            if (atfreelist == NULL)
                  return(NULL);
                              /* link new free list */
            upperlim = atfreelist + 8*(ATALLOCSZ-1);
            for (atp = atfreelist; atp < upperlim; atp += 8)
                  atp->kid = atp + 8;
            atp->kid = NULL;
      }
      atp = atfreelist;
      atfreelist = atp->kid;
      memset((char *)atp, '\0', 8*sizeof(AMBTREE));
      return(atp);
}


static void
freeambtree(                  /* free 8 ambient tree structs */
      AMBTREE  *atp
)
{
      atp->kid = atfreelist;
      atfreelist = atp;
}


static void
avinsert(                     /* insert ambient value in our tree */
      void *av
)
{
      register AMBTREE  *at;
      register AMBVAL  *ap;
      AMBVAL  avh;
      FVECT  ck0;
      double      s;
      int  branch;
      register int  i;

      if (((AMBVAL*)av)->rad <= FTINY)
            error(CONSISTENCY, "zero ambient radius in avinsert");
      at = &atrunk;
      VCOPY(ck0, thescene.cuorg);
      s = thescene.cusize;
      while (s*(OCTSCALE/2) > ((AMBVAL*)av)->rad*ambacc) {
            if (at->kid == NULL)
                  if ((at->kid = newambtree()) == NULL)
                        error(SYSTEM, "out of memory in avinsert");
            s *= 0.5;
            branch = 0;
            for (i = 0; i < 3; i++)
                  if (((AMBVAL*)av)->pos[i] > ck0[i] + s) {
                        ck0[i] += s;
                        branch |= 1 << i;
                  }
            at = at->kid + branch;
      }
      avh.next = at->alist;         /* order by increasing level */
      for (ap = &avh; ap->next != NULL; ap = ap->next)
            if (ap->next->lvl >= ((AMBVAL*)av)->lvl)
                  break;
      ((AMBVAL*)av)->next = ap->next;
      ap->next = (AMBVAL*)av;
      at->alist = avh.next;
}


static void
unloadatree(                  /* unload an ambient value tree */
      register AMBTREE  *at,
      unloadtf_t *f
)
{
      register AMBVAL  *av;
      register int  i;
                              /* transfer values at this node */
      for (av = at->alist; av != NULL; av = at->alist) {
            at->alist = av->next;
            (*f)(av);
      }
      if (at->kid == NULL)
            return;
      for (i = 0; i < 8; i++)       /* transfer and free children */
            unloadatree(at->kid+i, f);
      freeambtree(at->kid);
      at->kid = NULL;
}


static struct avl {
      AMBVAL      *p;
      unsigned long     t;
}     *avlist1;               /* ambient value list with ticks */
static AMBVAL     **avlist2;        /* memory positions for sorting */
static int  i_avlist;         /* index for lists */

static int alatcmp(const void *av1, const void *av2);

static void
av2list(
      void *av
)
{
#ifdef DEBUG
      if (i_avlist >= nambvals)
            error(CONSISTENCY, "too many ambient values in av2list1");
#endif
      avlist1[i_avlist].p = avlist2[i_avlist] = (AMBVAL*)av;
      avlist1[i_avlist++].t = ((AMBVAL*)av)->latick;
}


static int
alatcmp(                /* compare ambient values for MRA */
      const void *av1,
      const void *av2
)
{
      register long  lc = ((struct avl *)av2)->t - ((struct avl *)av1)->t;
      return(lc<0 ? -1 : lc>0 ? 1 : 0);
}


/* GW NOTE 2002/10/3:
 * I used to compare AMBVAL pointers, but found that this was the
 * cause of a serious consistency error with gcc, since the optimizer
 * uses some dangerous trick in pointer subtraction that
 * assumes pointers differ by exact struct size increments.
 */
static int
aposcmp(                /* compare ambient value positions */
      const void  *avp1,
      const void  *avp2
)
{
      register long     diff = *(char * const *)avp1 - *(char * const *)avp2;
      if (diff < 0)
            return(-1);
      return(diff > 0);
}

#if 1
static int
avlmemi(                      /* find list position from address */
      AMBVAL      *avaddr
)
{
      register AMBVAL  **avlpp;

      avlpp = (AMBVAL **)bsearch((char *)&avaddr, (char *)avlist2,
                  nambvals, sizeof(AMBVAL *), aposcmp);
      if (avlpp == NULL)
            error(CONSISTENCY, "address not found in avlmemi");
      return(avlpp - avlist2);
}
#else
#define avlmemi(avaddr) ((AMBVAL **)bsearch((char *)&avaddr,(char *)avlist2, \
                        nambvals,sizeof(AMBVAL *),aposcmp) - avlist2)
#endif


static void
sortambvals(                  /* resort ambient values */
      int   always
)
{
      AMBTREE  oldatrunk;
      AMBVAL      tav, *tap, *pnext;
      register int      i, j;
                              /* see if it's time yet */
      if (!always && (ambclock++ < lastsort+sortintvl ||
                  nambvals < SORT_THRESH))
            return;
      /*
       * The idea here is to minimize memory thrashing
       * in VM systems by improving reference locality.
       * We do this by periodically sorting our stored ambient
       * values in memory in order of most recently to least
       * recently accessed.  This ordering was chosen so that new
       * ambient values (which tend to be less important) go into
       * higher memory with the infrequently accessed values.
       *    Since we expect our values to need sorting less
       * frequently as the process continues, we double our
       * waiting interval after each call.
       *    This routine is also called by setambacc() with
       * the "always" parameter set to 1 so that the ambient
       * tree will be rebuilt with the new accuracy parameter.
       */
      if (tracktime) {        /* allocate pointer arrays to sort */
            avlist2 = (AMBVAL **)malloc(nambvals*sizeof(AMBVAL *));
            avlist1 = (struct avl *)malloc(nambvals*sizeof(struct avl));
      } else {
            avlist2 = NULL;
            avlist1 = NULL;
      }
      if (avlist1 == NULL) {        /* no time tracking -- rebuild tree? */
            if (avlist2 != NULL)
                  free((void *)avlist2);
            if (always) {           /* rebuild without sorting */
                  oldatrunk = atrunk;
                  atrunk.alist = NULL;
                  atrunk.kid = NULL;
                  unloadatree(&oldatrunk, avinsert);
            }
      } else {                /* sort memory by last access time */
            /*
             * Sorting memory is tricky because it isn't contiguous.
             * We have to sort an array of pointers by MRA and also
             * by memory position.  We then copy values in "loops"
             * to minimize memory hits.  Nevertheless, we will visit
             * everyone at least twice, and this is an expensive process
             * when we're thrashing, which is when we need to do it.
             */
#ifdef DEBUG
            sprintf(errmsg, "sorting %u ambient values at ambclock=%lu...",
                        nambvals, ambclock);
            eputs(errmsg);
#endif
            i_avlist = 0;
            unloadatree(&atrunk, av2list);      /* empty current tree */
#ifdef DEBUG
            if (i_avlist < nambvals)
                  error(CONSISTENCY, "missing ambient values in sortambvals");
#endif
            qsort((char *)avlist1, nambvals, sizeof(struct avl), alatcmp);
            qsort((char *)avlist2, nambvals, sizeof(AMBVAL *), aposcmp);
            for (i = 0; i < nambvals; i++) {
                  if (avlist1[i].p == NULL)
                        continue;
                  tap = avlist2[i];
                  tav = *tap;
                  for (j = i; (pnext = avlist1[j].p) != tap;
                              j = avlmemi(pnext)) {
                        *(avlist2[j]) = *pnext;
                        avinsert(avlist2[j]);
                        avlist1[j].p = NULL;
                  }
                  *(avlist2[j]) = tav;
                  avinsert(avlist2[j]);
                  avlist1[j].p = NULL;
            }
            free((void *)avlist1);
            free((void *)avlist2);
                                    /* compute new sort interval */
            sortintvl = ambclock - lastsort;
            if (sortintvl >= MAX_SORT_INTVL/2)
                  sortintvl = MAX_SORT_INTVL;
            else
                  sortintvl <<= 1;  /* wait twice as long next */
#ifdef DEBUG
            eputs("done\n");
#endif
      }
      if (ambclock >= MAXACLOCK)
            ambclock = MAXACLOCK/2;
      lastsort = ambclock;
}


#ifdef      F_SETLKW

static void
aflock(                 /* lock/unlock ambient file */
      int  typ
)
{
      static struct flock  fls;     /* static so initialized to zeroes */

      if (typ == fls.l_type)        /* already called? */
            return;
      fls.l_type = typ;
      if (fcntl(fileno(ambfp), F_SETLKW, &fls) < 0)
            error(SYSTEM, "cannot (un)lock ambient file");
}


extern int
ambsync(void)                 /* synchronize ambient file */
{
      long  flen;
      AMBVAL      avs;
      register int  n;

      if (ambfp == NULL)      /* no ambient file? */
            return(0);
                        /* gain appropriate access */
      aflock(nunflshed ? F_WRLCK : F_RDLCK);
                        /* see if file has grown */
      if ((flen = lseek(fileno(ambfp), (off_t)0, SEEK_END)) < 0)
            goto seekerr;
      if ( (n = flen - lastpos) ) {       /* file has grown */
            if (ambinp == NULL) {         /* use duplicate filedes */
                  ambinp = fdopen(dup(fileno(ambfp)), "r");
                  if (ambinp == NULL)
                        error(SYSTEM, "fdopen failed in ambsync");
            }
            if (fseek(ambinp, lastpos, SEEK_SET) < 0)
                  goto seekerr;
            while (n >= AMBVALSIZ) {      /* load contributed values */
                  if (!readambval(&avs, ambinp)) {
                        sprintf(errmsg,
                  "ambient file \"%s\" corrupted near character %ld",
                                    ambfile, flen - n);
                        error(WARNING, errmsg);
                        break;
                  }
                  avinsert(avstore(&avs));
                  n -= AMBVALSIZ;
            }
            lastpos = flen - n;
            /*** seek always as safety measure
            if (n) ***/             /* alignment */
                  if (lseek(fileno(ambfp), (off_t)lastpos, SEEK_SET) < 0)
                        goto seekerr;
      }
#ifdef  DEBUG
      if (ambfp->_ptr - ambfp->_base != nunflshed*AMBVALSIZ) {
            sprintf(errmsg, "ambient file buffer at %d rather than %d",
                        ambfp->_ptr - ambfp->_base,
                        nunflshed*AMBVALSIZ);
            error(CONSISTENCY, errmsg);
      }
#endif
      n = fflush(ambfp);                  /* calls write() at last */
      if (n != EOF)
            lastpos += (long)nunflshed*AMBVALSIZ;
      else if ((lastpos = lseek(fileno(ambfp), (off_t)0, SEEK_CUR)) < 0)
            goto seekerr;
            
      aflock(F_UNLCK);              /* release file */
      nunflshed = 0;
      return(n);
seekerr:
      error(SYSTEM, "seek failed in ambsync");
      return -1; /* pro forma return */
}

#else

extern int
ambsync(void)                 /* flush ambient file */
{
      if (ambfp == NULL)
            return(0);
      nunflshed = 0;
      return(fflush(ambfp));
}

#endif

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