src/rt/data.c

/* Copyright (c) 1991 Regents of the University of California */

#ifndef lint
static char SCCSid[] = "$SunId$ LBL";
#endif

/*
 *  data.c - routines dealing with interpolated data.
 *
 *     6/4/86
 */

#include  "standard.h"

#include  "color.h"

#include  "resolu.h"

#include  "data.h"


extern char  *fgetword();
extern double  atof();

extern char  *libpath;                  /* library search path */

static DATARRAY  *dlist = NULL;         /* data array list */

static DATARRAY  *plist = NULL;         /* picture list */


DATARRAY *
getdata(dname)                          /* get data array dname */
char  *dname;
{
        char  word[64];
        char  *dfname;
        FILE  *fp;
        int  asize;
        register int  i, j;
        register DATARRAY  *dp;
                                                /* look for array in list */
        for (dp = dlist; dp != NULL; dp = dp->next)
                if (!strcmp(dname, dp->name))
                        return(dp);             /* found! */

        /*
         *      If we haven't loaded the data already, we will look
         *  for it in the directorys specified by the library path.
         *
         *      The file has the following format:
         *
         *              N
         *              beg0    end0    n0
         *              beg1    end1    n1
         *              . . .
         *              begN    endN    nN
         *              data, later dimensions changing faster
         *              . . .
         *
         *      For irregularly spaced points, the following can be
         *  substituted for begi endi ni:
         *
         *              0 0 ni p0i p1i .. pni
         */

        if ((dfname = getpath(dname, libpath, R_OK)) == NULL) {
                sprintf(errmsg, "cannot find data file \"%s\"", dname);
                error(USER, errmsg);
        }
        if ((dp = (DATARRAY *)malloc(sizeof(DATARRAY))) == NULL)
                goto memerr;

        dp->name = savestr(dname);

        if ((fp = fopen(dfname, "r")) == NULL) {
                sprintf(errmsg, "cannot open data file \"%s\"", dfname);
                error(SYSTEM, errmsg);
        }
                                                        /* get dimensions */
        if (fgetword(word, sizeof(word), fp) == NULL || !isint(word))
                goto scanerr;
        dp->nd = atoi(word);
        if (dp->nd <= 0 || dp->nd > MAXDDIM) {
                sprintf(errmsg, "bad number of dimensions for \"%s\"", dname);
                error(USER, errmsg);
        }
        asize = 1;
        for (i = 0; i < dp->nd; i++) {
                if (fgetword(word, sizeof(word), fp) == NULL || !isflt(word))
                        goto scanerr;
                dp->dim[i].org = atof(word);
                if (fgetword(word, sizeof(word), fp) == NULL || !isflt(word))
                        goto scanerr;
                dp->dim[i].siz = atof(word);
                if (fgetword(word, sizeof(word), fp) == NULL || !isint(word))
                        goto scanerr;
                dp->dim[i].ne = atoi(word);
                if (dp->dim[i].ne < 2)
                        goto scanerr;
                asize *= dp->dim[i].ne;
                if ((dp->dim[i].siz -= dp->dim[i].org) == 0) {
                        dp->dim[i].p = (double *)malloc(dp->dim[i].ne*sizeof(double));
                        if (dp->dim[i].p == NULL)
                                goto memerr;
                        for (j = 0; j < dp->dim[i].ne; j++) {
                                if (fgetword(word, sizeof(word), fp) == NULL ||
                                                !isflt(word))
                                        goto scanerr;
                                dp->dim[i].p[j] = atof(word);
                        }
                        for (j = 1; j < dp->dim[i].ne-1; j++)
                                if ((dp->dim[i].p[j-1] < dp->dim[i].p[j]) !=
                                        (dp->dim[i].p[j] < dp->dim[i].p[j+1]))
                                        goto scanerr;
                        dp->dim[i].org = dp->dim[i].p[0];
                        dp->dim[i].siz = dp->dim[i].p[dp->dim[i].ne-1]
                                                - dp->dim[i].p[0];
                } else
                        dp->dim[i].p = NULL;
        }
        if ((dp->arr = (DATATYPE *)malloc(asize*sizeof(DATATYPE))) == NULL)
                goto memerr;
        
        for (i = 0; i < asize; i++) {
                if (fgetword(word, sizeof(word), fp) == NULL || !isflt(word))
                        goto scanerr;
                dp->arr[i] = atof(word);
        }
        fclose(fp);
        dp->next = dlist;
        return(dlist = dp);

memerr:
        error(SYSTEM, "out of memory in getdata");
scanerr:
        sprintf(errmsg, "%s in data file \"%s\"",
                        feof(fp) ? "unexpected EOF" : "bad format", dfname);
        error(USER, errmsg);
}


static double  inpaspect;               /* aspect ratio of input picture */

static
headaspect(s)                           /* check string for aspect ratio */
char  *s;
{
        if (isaspect(s))
                inpaspect *= aspectval(s);
}


DATARRAY *
getpict(pname)                          /* get picture pname */
char  *pname;
{
        extern char  *libpath;
        char  *pfname;
        FILE  *fp;
        COLOR  *scanin;
        int  sl, ns;
        RESOLU  inpres;
        FLOAT  loc[2];
        int  y;
        register int  x, i;
        register DATARRAY  *pp;
                                                /* look for array in list */
        for (pp = plist; pp != NULL; pp = pp->next)
                if (!strcmp(pname, pp->name))
                        return(pp);             /* found! */

        if ((pfname = getpath(pname, libpath, R_OK)) == NULL) {
                sprintf(errmsg, "cannot find picture file \"%s\"", pname);
                error(USER, errmsg);
        }
        if ((pp = (DATARRAY *)calloc(3, sizeof(DATARRAY))) == NULL)
                goto memerr;

        pp[0].name = 
        pp[1].name =
        pp[2].name = savestr(pname);

        if ((fp = fopen(pfname, "r")) == NULL) {
                sprintf(errmsg, "cannot open picture file \"%s\"", pfname);
                error(SYSTEM, errmsg);
        }
                                                /* get dimensions */
        inpaspect = 1.0;
        getheader(fp, headaspect);
        if (!fgetsresolu(&inpres, fp))
                goto readerr;
        for (i = 0; i < 3; i++) {
                pp[i].nd = 2;
                pp[i].dim[0].ne = inpres.yr;
                pp[i].dim[1].ne = inpres.xr;
                pp[i].dim[0].org =
                pp[i].dim[1].org = 0.0;
                if (inpres.xr <= inpres.yr*inpaspect) {
                        pp[i].dim[0].siz = inpaspect *
                                                (double)inpres.yr/inpres.xr;
                        pp[i].dim[1].siz = 1.0;
                } else {
                        pp[i].dim[0].siz = 1.0;
                        pp[i].dim[1].siz = (double)inpres.xr/inpres.yr /
                                                inpaspect;
                }
                pp[i].dim[0].p = pp[i].dim[1].p = NULL;
                pp[i].arr = (DATATYPE *)
                                malloc(inpres.xr*inpres.yr*sizeof(DATATYPE));
                if (pp[i].arr == NULL)
                        goto memerr;
        }
                                                        /* load picture */
        sl = scanlen(&inpres);
        ns = numscans(&inpres);
        if ((scanin = (COLOR *)malloc(sl*sizeof(COLOR))) == NULL)
                goto memerr;
        for (y = 0; y < ns; y++) {
                if (freadscan(scanin, sl, fp) < 0)
                        goto readerr;
                for (x = 0; x < sl; x++) {
                        pix2loc(loc, &inpres, x, y);
                        i = (int)(loc[1]*inpres.yr)*inpres.xr +
                                        (int)(loc[0]*inpres.xr);
                        pp[0].arr[i] = colval(scanin[x],RED);
                        pp[1].arr[i] = colval(scanin[x],GRN);
                        pp[2].arr[i] = colval(scanin[x],BLU);
                }
        }
        free((char *)scanin);
        fclose(fp);
        pp[0].next =
        pp[1].next =
        pp[2].next = plist;
        return(plist = pp);

memerr:
        error(SYSTEM, "out of memory in getpict");
readerr:
        sprintf(errmsg, "bad picture file \"%s\"", pfname);
        error(USER, errmsg);
}


freedata(dname)                 /* free memory associated with dname */
char  *dname;
{
        register DATARRAY  *dp, *dpl;
        register int  i;

        for (dpl = NULL, dp = dlist; dp != NULL; dpl = dp, dp = dp->next)
                if (!strcmp(dname, dp->name)) {
                        if (dpl == NULL)
                                dlist = dp->next;
                        else
                                dpl->next = dp->next;
                        free((char *)dp->arr);
                        for (i = 0; i < dp->nd; i++)
                                if (dp->dim[i].p != NULL)
                                        free((char *)dp->dim[i].p);
                        freestr(dp->name);
                        free((char *)dp);
                        return;
                }
}


freepict(pname)                 /* free memory associated with pname */
char  *pname;
{
        register DATARRAY  *pp, *ppl;

        for (ppl = NULL, pp = plist; pp != NULL; ppl = pp, pp = pp->next)
                if (!strcmp(pname, pp->name)) {
                        if (ppl == NULL)
                                plist = pp->next;
                        else
                                ppl->next = pp->next;
                        free((char *)pp[0].arr);
                        free((char *)pp[1].arr);
                        free((char *)pp[2].arr);
                        freestr(pp[0].name);
                        free((char *)pp);
                        return;
                }
}


double
datavalue(dp, pt)               /* interpolate data value at a point */
register DATARRAY  *dp;
double  *pt;
{
        DATARRAY  sd;
        int  asize;
        int  lower, upper;
        register int  i;
        double  x, y, y0, y1;
                                        /* set up dimensions for recursion */
        sd.nd = dp->nd - 1;
        asize = 1;
        for (i = 0; i < sd.nd; i++) {
                sd.dim[i].org = dp->dim[i+1].org;
                sd.dim[i].siz = dp->dim[i+1].siz;
                sd.dim[i].p = dp->dim[i+1].p;
                asize *= sd.dim[i].ne = dp->dim[i+1].ne;
        }
                                        /* get independent variable */
        if (dp->dim[0].p == NULL) {             /* evenly spaced points */
                x = (pt[0] - dp->dim[0].org)/dp->dim[0].siz;
                x = x * (dp->dim[0].ne - 1);
                i = x;
                if (i < 0)
                        i = 0;
                else if (i > dp->dim[0].ne - 2)
                        i = dp->dim[0].ne - 2;
        } else {                                /* unevenly spaced points */
                if (dp->dim[0].siz > 0.0) {
                        lower = 0;
                        upper = dp->dim[0].ne;
                } else {
                        lower = dp->dim[0].ne;
                        upper = 0;
                }
                do {
                        i = (lower + upper) >> 1;
                        if (pt[0] >= dp->dim[0].p[i])
                                lower = i;
                        else
                                upper = i;
                } while (i != (lower + upper) >> 1);
                if (i > dp->dim[0].ne - 2)
                        i = dp->dim[0].ne - 2;
                x = i + (pt[0] - dp->dim[0].p[i]) /
                                (dp->dim[0].p[i+1] - dp->dim[0].p[i]);
        }
                                        /* get dependent variable */
        if (dp->nd == 1) {
                y0 = dp->arr[i];
                y1 = dp->arr[i+1];
        } else {
                sd.arr = &dp->arr[i*asize];
                y0 = datavalue(&sd, pt+1);
                sd.arr = &dp->arr[(i+1)*asize];
                y1 = datavalue(&sd, pt+1);
        }
        /*
         * Extrapolate as far as one division, then
         * taper off harmonically to zero.
         */
        if (x > i+2)
                y = (2*y1-y0)/(x-i-1);
        else if (x < i-1)
                y = (2*y0-y1)/(i-x);
        else
                y = y0*((i+1)-x) + y1*(x-i);

        return(y);
}
Revision:	1.11
Committed:	Mon Nov 11 14:02:43 1991 UTC (32 years, 5 months ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 1.10:	+30 -16 lines
Log Message:	Improved handling of scanline ordering
#	User	Rev	Content
1	greg	1.8	/* Copyright (c) 1991 Regents of the University of California */
2	greg	1.1
3			#ifndef lint
4			static char SCCSid[] = "$SunId$ LBL";
5			#endif
6
7			/*
8			* data.c - routines dealing with interpolated data.
9			*
10			* 6/4/86
11			*/
12
13			#include "standard.h"
14
15			#include "color.h"
16
17	greg	1.11	#include "resolu.h"
18
19	greg	1.1	#include "data.h"
20
21
22	greg	1.10	extern char *fgetword();
23			extern double atof();
24
25	greg	1.1	extern char libpath; / library search path */
26
27			static DATARRAY dlist = NULL; / data array list */
28
29			static DATARRAY plist = NULL; / picture list */
30
31
32			DATARRAY *
33			getdata(dname) /* get data array dname */
34			char *dname;
35			{
36	greg	1.10	char word[64];
37	greg	1.1	char *dfname;
38			FILE *fp;
39			int asize;
40	greg	1.4	register int i, j;
41	greg	1.1	register DATARRAY *dp;
42			/* look for array in list */
43			for (dp = dlist; dp != NULL; dp = dp->next)
44			if (!strcmp(dname, dp->name))
45			return(dp); /* found! */
46
47			/*
48			* If we haven't loaded the data already, we will look
49			* for it in the directorys specified by the library path.
50			*
51			* The file has the following format:
52			*
53	greg	1.4	* N
54	greg	1.1	* beg0 end0 n0
55			* beg1 end1 n1
56			* . . .
57	greg	1.4	* begN endN nN
58	greg	1.1	* data, later dimensions changing faster
59			* . . .
60			*
61	greg	1.4	* For irregularly spaced points, the following can be
62			* substituted for begi endi ni:
63			*
64	greg	1.6	* 0 0 ni p0i p1i .. pni
65	greg	1.1	*/
66
67	greg	1.2	if ((dfname = getpath(dname, libpath, R_OK)) == NULL) {
68	greg	1.1	sprintf(errmsg, "cannot find data file \"%s\"", dname);
69			error(USER, errmsg);
70			}
71			if ((dp = (DATARRAY *)malloc(sizeof(DATARRAY))) == NULL)
72			goto memerr;
73
74			dp->name = savestr(dname);
75
76			if ((fp = fopen(dfname, "r")) == NULL) {
77			sprintf(errmsg, "cannot open data file \"%s\"", dfname);
78			error(SYSTEM, errmsg);
79			}
80			/* get dimensions */
81	greg	1.10	if (fgetword(word, sizeof(word), fp) == NULL \|\| !isint(word))
82	greg	1.1	goto scanerr;
83	greg	1.10	dp->nd = atoi(word);
84	greg	1.9	if (dp->nd <= 0 \|\| dp->nd > MAXDDIM) {
85	greg	1.1	sprintf(errmsg, "bad number of dimensions for \"%s\"", dname);
86			error(USER, errmsg);
87			}
88			asize = 1;
89			for (i = 0; i < dp->nd; i++) {
90	greg	1.10	if (fgetword(word, sizeof(word), fp) == NULL \|\| !isflt(word))
91	greg	1.6	goto scanerr;
92	greg	1.10	dp->dim[i].org = atof(word);
93			if (fgetword(word, sizeof(word), fp) == NULL \|\| !isflt(word))
94			goto scanerr;
95			dp->dim[i].siz = atof(word);
96			if (fgetword(word, sizeof(word), fp) == NULL \|\| !isint(word))
97			goto scanerr;
98			dp->dim[i].ne = atoi(word);
99	greg	1.6	if (dp->dim[i].ne < 2)
100			goto scanerr;
101			asize *= dp->dim[i].ne;
102			if ((dp->dim[i].siz -= dp->dim[i].org) == 0) {
103	greg	1.4	dp->dim[i].p = (double )malloc(dp->dim[i].nesizeof(double));
104			if (dp->dim[i].p == NULL)
105			goto memerr;
106	greg	1.10	for (j = 0; j < dp->dim[i].ne; j++) {
107			if (fgetword(word, sizeof(word), fp) == NULL \|\|
108			!isflt(word))
109	greg	1.4	goto scanerr;
110	greg	1.10	dp->dim[i].p[j] = atof(word);
111			}
112	greg	1.4	for (j = 1; j < dp->dim[i].ne-1; j++)
113			if ((dp->dim[i].p[j-1] < dp->dim[i].p[j]) !=
114			(dp->dim[i].p[j] < dp->dim[i].p[j+1]))
115			goto scanerr;
116			dp->dim[i].org = dp->dim[i].p[0];
117			dp->dim[i].siz = dp->dim[i].p[dp->dim[i].ne-1]
118			- dp->dim[i].p[0];
119			} else
120	greg	1.6	dp->dim[i].p = NULL;
121	greg	1.1	}
122			if ((dp->arr = (DATATYPE )malloc(asizesizeof(DATATYPE))) == NULL)
123			goto memerr;
124
125	greg	1.10	for (i = 0; i < asize; i++) {
126			if (fgetword(word, sizeof(word), fp) == NULL \|\| !isflt(word))
127	greg	1.1	goto scanerr;
128	greg	1.10	dp->arr[i] = atof(word);
129			}
130	greg	1.1	fclose(fp);
131			dp->next = dlist;
132			return(dlist = dp);
133
134			memerr:
135			error(SYSTEM, "out of memory in getdata");
136			scanerr:
137			sprintf(errmsg, "%s in data file \"%s\"",
138			feof(fp) ? "unexpected EOF" : "bad format", dfname);
139			error(USER, errmsg);
140			}
141
142
143	greg	1.5	static double inpaspect; /* aspect ratio of input picture */
144
145			static
146			headaspect(s) /* check string for aspect ratio */
147			char *s;
148			{
149			if (isaspect(s))
150			inpaspect *= aspectval(s);
151			}
152
153
154	greg	1.1	DATARRAY *
155			getpict(pname) /* get picture pname */
156			char *pname;
157			{
158			extern char *libpath;
159			char *pfname;
160			FILE *fp;
161			COLOR *scanin;
162	greg	1.11	int sl, ns;
163			RESOLU inpres;
164			FLOAT loc[2];
165			int y;
166			register int x, i;
167	greg	1.1	register DATARRAY *pp;
168			/* look for array in list */
169			for (pp = plist; pp != NULL; pp = pp->next)
170			if (!strcmp(pname, pp->name))
171			return(pp); /* found! */
172
173	greg	1.2	if ((pfname = getpath(pname, libpath, R_OK)) == NULL) {
174	greg	1.1	sprintf(errmsg, "cannot find picture file \"%s\"", pname);
175			error(USER, errmsg);
176			}
177			if ((pp = (DATARRAY *)calloc(3, sizeof(DATARRAY))) == NULL)
178			goto memerr;
179
180			pp[0].name =
181			pp[1].name =
182			pp[2].name = savestr(pname);
183
184			if ((fp = fopen(pfname, "r")) == NULL) {
185			sprintf(errmsg, "cannot open picture file \"%s\"", pfname);
186			error(SYSTEM, errmsg);
187			}
188			/* get dimensions */
189	greg	1.5	inpaspect = 1.0;
190			getheader(fp, headaspect);
191	greg	1.11	if (!fgetsresolu(&inpres, fp))
192	greg	1.1	goto readerr;
193			for (i = 0; i < 3; i++) {
194			pp[i].nd = 2;
195	greg	1.11	pp[i].dim[0].ne = inpres.yr;
196			pp[i].dim[1].ne = inpres.xr;
197	greg	1.1	pp[i].dim[0].org =
198			pp[i].dim[1].org = 0.0;
199	greg	1.11	if (inpres.xr <= inpres.yr*inpaspect) {
200			pp[i].dim[0].siz = inpaspect *
201			(double)inpres.yr/inpres.xr;
202	greg	1.7	pp[i].dim[1].siz = 1.0;
203			} else {
204	greg	1.1	pp[i].dim[0].siz = 1.0;
205	greg	1.11	pp[i].dim[1].siz = (double)inpres.xr/inpres.yr /
206			inpaspect;
207	greg	1.1	}
208	greg	1.7	pp[i].dim[0].p = pp[i].dim[1].p = NULL;
209	greg	1.11	pp[i].arr = (DATATYPE *)
210			malloc(inpres.xrinpres.yrsizeof(DATATYPE));
211	greg	1.1	if (pp[i].arr == NULL)
212			goto memerr;
213			}
214			/* load picture */
215	greg	1.11	sl = scanlen(&inpres);
216			ns = numscans(&inpres);
217			if ((scanin = (COLOR )malloc(slsizeof(COLOR))) == NULL)
218	greg	1.1	goto memerr;
219	greg	1.11	for (y = 0; y < ns; y++) {
220			if (freadscan(scanin, sl, fp) < 0)
221	greg	1.1	goto readerr;
222	greg	1.11	for (x = 0; x < sl; x++) {
223			pix2loc(loc, &inpres, x, y);
224			i = (int)(loc[1]inpres.yr)inpres.xr +
225			(int)(loc[0]*inpres.xr);
226			pp[0].arr[i] = colval(scanin[x],RED);
227			pp[1].arr[i] = colval(scanin[x],GRN);
228			pp[2].arr[i] = colval(scanin[x],BLU);
229			}
230	greg	1.1	}
231			free((char *)scanin);
232			fclose(fp);
233			pp[0].next =
234			pp[1].next =
235			pp[2].next = plist;
236			return(plist = pp);
237
238			memerr:
239			error(SYSTEM, "out of memory in getpict");
240			readerr:
241			sprintf(errmsg, "bad picture file \"%s\"", pfname);
242			error(USER, errmsg);
243			}
244
245
246			freedata(dname) /* free memory associated with dname */
247			char *dname;
248			{
249			register DATARRAY dp, dpl;
250	greg	1.4	register int i;
251	greg	1.1
252			for (dpl = NULL, dp = dlist; dp != NULL; dpl = dp, dp = dp->next)
253			if (!strcmp(dname, dp->name)) {
254			if (dpl == NULL)
255			dlist = dp->next;
256			else
257			dpl->next = dp->next;
258			free((char *)dp->arr);
259	greg	1.4	for (i = 0; i < dp->nd; i++)
260			if (dp->dim[i].p != NULL)
261			free((char *)dp->dim[i].p);
262	greg	1.1	freestr(dp->name);
263			free((char *)dp);
264			return;
265			}
266			}
267
268
269			freepict(pname) /* free memory associated with pname */
270			char *pname;
271			{
272			register DATARRAY pp, ppl;
273
274			for (ppl = NULL, pp = plist; pp != NULL; ppl = pp, pp = pp->next)
275			if (!strcmp(pname, pp->name)) {
276			if (ppl == NULL)
277			plist = pp->next;
278			else
279			ppl->next = pp->next;
280			free((char *)pp[0].arr);
281			free((char *)pp[1].arr);
282			free((char *)pp[2].arr);
283			freestr(pp[0].name);
284			free((char *)pp);
285			return;
286			}
287			}
288
289
290			double
291			datavalue(dp, pt) /* interpolate data value at a point */
292			register DATARRAY *dp;
293			double *pt;
294			{
295			DATARRAY sd;
296			int asize;
297	greg	1.6	int lower, upper;
298	greg	1.1	register int i;
299			double x, y, y0, y1;
300	greg	1.4	/* set up dimensions for recursion */
301	greg	1.1	sd.nd = dp->nd - 1;
302			asize = 1;
303			for (i = 0; i < sd.nd; i++) {
304			sd.dim[i].org = dp->dim[i+1].org;
305			sd.dim[i].siz = dp->dim[i+1].siz;
306	greg	1.4	sd.dim[i].p = dp->dim[i+1].p;
307	greg	1.1	asize *= sd.dim[i].ne = dp->dim[i+1].ne;
308			}
309	greg	1.4	/* get independent variable */
310			if (dp->dim[0].p == NULL) { /* evenly spaced points */
311			x = (pt[0] - dp->dim[0].org)/dp->dim[0].siz;
312			x = x * (dp->dim[0].ne - 1);
313			i = x;
314			if (i < 0)
315			i = 0;
316			else if (i > dp->dim[0].ne - 2)
317			i = dp->dim[0].ne - 2;
318			} else { /* unevenly spaced points */
319	greg	1.6	if (dp->dim[0].siz > 0.0) {
320			lower = 0;
321			upper = dp->dim[0].ne;
322			} else {
323			lower = dp->dim[0].ne;
324			upper = 0;
325			}
326			do {
327			i = (lower + upper) >> 1;
328			if (pt[0] >= dp->dim[0].p[i])
329			lower = i;
330	greg	1.8	else
331	greg	1.6	upper = i;
332			} while (i != (lower + upper) >> 1);
333	greg	1.8	if (i > dp->dim[0].ne - 2)
334	greg	1.4	i = dp->dim[0].ne - 2;
335			x = i + (pt[0] - dp->dim[0].p[i]) /
336			(dp->dim[0].p[i+1] - dp->dim[0].p[i]);
337			}
338			/* get dependent variable */
339	greg	1.1	if (dp->nd == 1) {
340			y0 = dp->arr[i];
341			y1 = dp->arr[i+1];
342			} else {
343			sd.arr = &dp->arr[i*asize];
344			y0 = datavalue(&sd, pt+1);
345			sd.arr = &dp->arr[(i+1)*asize];
346			y1 = datavalue(&sd, pt+1);
347			}
348			/*
349			* Extrapolate as far as one division, then
350			* taper off harmonically to zero.
351			*/
352			if (x > i+2)
353			y = (2*y1-y0)/(x-i-1);
354			else if (x < i-1)
355			y = (2*y0-y1)/(i-x);
356			else
357			y = y0((i+1)-x) + y1(x-i);
358
359			return(y);
360			}