/*============================================================================
  WCSLIB 8.7 - an implementation of the FITS WCS standard.
  Copyright (C) 1995-2026, Mark Calabretta

  This file is part of WCSLIB.

  WCSLIB is free software: you can redistribute it and/or modify it under the
  terms of the GNU Lesser General Public License as published by the Free
  Software Foundation, either version 3 of the License, or (at your option)
  any later version.

  WCSLIB is distributed in the hope that it will be useful, but WITHOUT ANY
  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
  more details.

  You should have received a copy of the GNU Lesser General Public License
  along with WCSLIB.  If not, see http://www.gnu.org/licenses.

  Author: Mark Calabretta, Australia Telescope National Facility, CSIRO.
  http://www.atnf.csiro.au/computing/software/wcs
  $Id: tab.c,v 8.7 2026/05/11 12:01:10 mcalabre Exp $
*===========================================================================*/

#include <limits.h>
#include <math.h>
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

#include "wcserr.h"
#include "wcsmath.h"
#include "wcsprintf.h"
#include "wcsutil.h"
#include "tab.h"

// Map status return value to message.
const char *tab_errmsg[] = {
  "Success",
  "Null tabprm pointer passed",
  "Memory allocation failed",
  "Invalid tabular parameters",
  "One or more of the x coordinates were invalid",
  "One or more of the world coordinates were invalid"};

static const int TABSET = 137;

// Convenience macro for invoking wcserr_set().
#define TAB_ERRMSG(status) WCSERR_SET(status), tab_errmsg[status]

//----------------------------------------------------------------------------

int tabini(int alloc, int M, const int K[], struct tabprm *tab)

{
  static const char *function = "tabini";

  if (tab == 0x0) return TABERR_NULL_POINTER;

  // Initialize error message handling.
  if (tab->flag == -1) {
    tab->err = 0x0;
  }
  struct wcserr **err = &(tab->err);
  wcserr_clear(err);


  if (M <= 0) {
    return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
      "M must be positive, got %d", M);
  }

  // Determine the total number of elements in the coordinate array.
  int N;
  if (K) {
    N = M;

    for (int m = 0; m < M; m++) {
      if (K[m] < 0) {
        return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
          "Invalid tabular parameters: Each element of K must be "
          "non-negative, got %d", K[m]);
      }

      if (N < INT_MAX / K[m]) {
        N *= K[m];
      } else {
        return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
          "Invalid tabular parameters: No. elements in coordinate "
          "array exceeds INT_MAX");
      }
    }

  } else {
    // Axis lengths as yet unknown.
    N = 0;
  }


  // Initialize memory management.
  if (tab->flag == -1 || tab->m_flag != TABSET) {
    if (tab->flag == -1) {
      tab->sense   = 0x0;
      tab->p0      = 0x0;
      tab->delta   = 0x0;
      tab->extrema = 0x0;
      tab->set_M   = 0;
    }

    tab->m_flag  = 0;
    tab->m_M     = 0;
    tab->m_N     = 0;
    tab->m_K     = 0x0;
    tab->m_map   = 0x0;
    tab->m_crval = 0x0;
    tab->m_index = 0x0;
    tab->m_indxs = 0x0;
    tab->m_coord = 0x0;

  } else {
    // Clear any outstanding signals set by wcstab().
    for (int m = 0; m < tab->m_M; m++) {
      if (tab->m_indxs[m] == (double *)0x1) tab->m_indxs[m] = 0x0;
    }

    if (tab->m_coord == (double *)0x1) tab->m_coord = 0x0;
  }


  // Allocate memory for arrays if required.
  if (alloc ||
     tab->K == 0x0 ||
     tab->map == 0x0 ||
     tab->crval == 0x0 ||
     tab->index == 0x0 ||
     tab->coord == 0x0) {

    // Was sufficient allocated previously?
    if (tab->m_flag == TABSET && (tab->m_M < M || tab->m_N < N)) {
      // No, free it.
      tabfree(tab);
    }

    if (alloc || tab->K == 0x0) {
      if (tab->m_K) {
        // In case the caller fiddled with it.
        tab->K = tab->m_K;

      } else {
        if (!(tab->K = calloc(M, sizeof(int)))) {
          return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
        }

        tab->m_flag = TABSET;
        tab->m_M = M;
        tab->m_K = tab->K;
      }
    }

    if (alloc || tab->map == 0x0) {
      if (tab->m_map) {
        // In case the caller fiddled with it.
        tab->map = tab->m_map;

      } else {
        if (!(tab->map = calloc(M, sizeof(int)))) {
          return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
        }

        tab->m_flag = TABSET;
        tab->m_M = M;
        tab->m_map = tab->map;
      }
    }

    if (alloc || tab->crval == 0x0) {
      if (tab->m_crval) {
        // In case the caller fiddled with it.
        tab->crval = tab->m_crval;

      } else {
        if (!(tab->crval = calloc(M, sizeof(double)))) {
          return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
        }

        tab->m_flag = TABSET;
        tab->m_M = M;
        tab->m_crval = tab->crval;
      }
    }

    if (alloc || tab->index == 0x0) {
      if (tab->m_index) {
        // In case the caller fiddled with it.
        tab->index = tab->m_index;

      } else {
        if (!(tab->index = (double **)calloc(M, sizeof(double *)))) {
          return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
        }

        tab->m_flag = TABSET;
        tab->m_M = M;
        tab->m_N = N;
        tab->m_index = tab->index;

        if (!(tab->m_indxs = (double **)calloc(M, sizeof(double *)))) {
          return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
        }

        // Recall that calloc() initializes these pointers to zero.
        if (K) {
          for (int m = 0; m < M; m++) {
            if (K[m]) {
              if (!(tab->index[m] = calloc(K[m], sizeof(double)))) {
                return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
              }

              tab->m_indxs[m] = tab->index[m];
            }
          }
        }
      }
    }

    if (alloc || tab->coord == 0x0) {
      if (tab->m_coord) {
        // In case the caller fiddled with it.
        tab->coord = tab->m_coord;

      } else if (N) {
        if (!(tab->coord = calloc(N, sizeof(double)))) {
          return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
        }

        tab->m_flag = TABSET;
        tab->m_M = M;
        tab->m_N = N;
        tab->m_coord = tab->coord;
      }
    }
  }

  tab->M = M;

  // Set defaults.
  for (int m = 0; m < M; m++) {
    tab->map[m] = -1;
    tab->crval[m] = 0.0;

    if (K) {
      tab->K[m] = K[m];
      double *dp;
      if ((dp = tab->index[m])) {
        // Table indexes are 1-relative.
        for (int k = 1; k <= K[m]; k++) {
          *(dp++) = k;
        }
      }
    } else {
      tab->K[m] = 0;
    }
  }

  // Initialize the coordinate array.
  for (double *dp = tab->coord; dp < tab->coord + N; dp++) {
    *dp = UNDEFINED;
  }

  tab->flag = 0;

  return 0;
}

//----------------------------------------------------------------------------

int tabmem(struct tabprm *tab)

{
  static const char *function = "tabmem";

  if (tab == 0x0) return TABERR_NULL_POINTER;
  struct wcserr **err = &(tab->err);

  if (tab->M == 0 || tab->K == 0x0) {
    // Should have been set by this time.
    return wcserr_set(WCSERR_SET(TABERR_MEMORY),
      "Null pointers in tabprm struct");
  }


  int M = tab->M;
  int N = M;
  for (int m = 0; m < M; m++) {
    if (tab->K[m] < 0) {
      return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
        "Invalid tabular parameters: Each element of K must be "
        "non-negative, got K[%d] = %d", m, tab->K[m]);
    }

    N *= tab->K[m];
  }


  if (tab->m_M == 0) {
    tab->m_M = M;
  } else if (tab->m_M < M) {
    // Only possible if the user changed M.
    return wcserr_set(WCSERR_SET(TABERR_MEMORY),
      "tabprm struct inconsistent");
  }

  if (tab->m_N == 0) {
    tab->m_N = N;
  } else if (tab->m_N < N) {
    // Only possible if the user changed K[].
    return wcserr_set(WCSERR_SET(TABERR_MEMORY),
      "tabprm struct inconsistent");
  }

  if (tab->m_K == 0x0) {
    if ((tab->m_K = tab->K)) {
      tab->m_flag = TABSET;
    }
  }

  if (tab->m_map == 0x0) {
    if ((tab->m_map = tab->map)) {
      tab->m_flag = TABSET;
    }
  }

  if (tab->m_crval == 0x0) {
    if ((tab->m_crval = tab->crval)) {
      tab->m_flag = TABSET;
    }
  }

  if (tab->m_index == 0x0) {
    if ((tab->m_index = tab->index)) {
      tab->m_flag = TABSET;
    }
  }

  // Check memory allocation, balm for static code analysers.
  if (tab->index == 0x0) {
    // Not ppossible if tabini() has been called.
    return wcserr_set(WCSERR_SET(TABERR_MEMORY),
      "Null index in tabprm struct");
  }

  for (int m = 0; m < tab->m_M; m++) {
    if (tab->m_indxs[m] == 0x0 || tab->m_indxs[m] == (double *)0x1) {
      if ((tab->m_indxs[m] = tab->index[m])) {
        tab->m_flag = TABSET;
      }
    }
  }

  if (tab->m_coord == 0x0 || tab->m_coord == (double *)0x1) {
    if ((tab->m_coord = tab->coord)) {
      tab->m_flag = TABSET;
    }
  }

  tab->flag = 0;

  return 0;
}

//----------------------------------------------------------------------------

int tabcpy(int alloc, const struct tabprm *tabsrc, struct tabprm *tabdst)

{
  static const char *function = "tabcpy";

  if (tabsrc == 0x0) return TABERR_NULL_POINTER;
  if (tabdst == 0x0) return TABERR_NULL_POINTER;
  struct wcserr **err = &(tabdst->err);

  int M = tabsrc->M;
  if (M <= 0) {
    return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
      "M must be positive, got %d", M);
  }

  int status;
  if ((status = tabini(alloc, M, tabsrc->K, tabdst))) {
    return status;
  }

  int N = M;
  for (int m = 0; m < M; m++) {
    tabdst->map[m]   = tabsrc->map[m];
    tabdst->crval[m] = tabsrc->crval[m];
    N *= tabsrc->K[m];
  }

  double *dstp, *srcp;
  for (int m = 0; m < M; m++) {
    if ((srcp = tabsrc->index[m])) {
      dstp = tabdst->index[m];
      for (int k = 0; k < tabsrc->K[m]; k++) {
        *(dstp++) = *(srcp++);
      }
    } else {
      if (tabdst->m_indxs && tabdst->m_indxs[m]) {
        free(tabdst->m_indxs[m]);
        tabdst->index[m]   = 0x0;
        tabdst->m_indxs[m] = 0x0;
      }
    }
  }

  srcp = tabsrc->coord;
  dstp = tabdst->coord;
  for (int n = 0; n < N; n++) {
    *(dstp++) = *(srcp++);
  }

  return 0;
}

//----------------------------------------------------------------------------

int tabcmp(
  int dummy,
  double tol,
  const struct tabprm *tab1,
  const struct tabprm *tab2,
  int *equal)

{
  // Avert nuisance compiler warnings about unused parameters.
  (void)dummy;

  if (tab1  == 0x0) return TABERR_NULL_POINTER;
  if (tab2  == 0x0) return TABERR_NULL_POINTER;
  if (equal == 0x0) return TABERR_NULL_POINTER;

  *equal = 0;

  if (tab1->M != tab2->M) {
    return 0;
  }

  int M = tab1->M;

  if (!wcsutil_intEq(M, tab1->K, tab2->K) ||
      !wcsutil_intEq(M, tab1->map, tab2->map) ||
      !wcsutil_dblEq(M, tol, tab1->crval, tab2->crval)) {
    return 0;
  }

  int N = M;
  for (int m = 0; m < M; m++) {
    if (!wcsutil_dblEq(tab1->K[m], tol, tab1->index[m], tab2->index[m])) {
      return 0;
    }

    N *= tab1->K[m];
  }

  if (!wcsutil_dblEq(N, tol, tab1->coord, tab2->coord)) {
    return 0;
  }

  *equal = 1;

  return 0;
}


//----------------------------------------------------------------------------

int tabfree(struct tabprm *tab)

{
  if (tab == 0x0) return TABERR_NULL_POINTER;

  if (tab->flag != -1) {
    // Clear any outstanding signals set by wcstab().
    for (int m = 0; m < tab->m_M; m++) {
      if (tab->m_indxs[m] == (double *)0x1) tab->m_indxs[m] = 0x0;
    }

    if (tab->m_coord == (double *)0x1) tab->m_coord = 0x0;

    // Free memory allocated by tabini().
    if (tab->m_flag == TABSET) {
      if (tab->K     == tab->m_K)     tab->K = 0x0;
      if (tab->map   == tab->m_map)   tab->map = 0x0;
      if (tab->crval == tab->m_crval) tab->crval = 0x0;
      if (tab->index == tab->m_index) tab->index = 0x0;
      if (tab->coord == tab->m_coord) tab->coord = 0x0;

      if (tab->m_K)     free(tab->m_K);
      if (tab->m_map)   free(tab->m_map);
      if (tab->m_crval) free(tab->m_crval);

      if (tab->m_index) {
        for (int m = 0; m < tab->m_M; m++) {
          if (tab->m_indxs[m]) free(tab->m_indxs[m]);
        }
        free((void *)tab->m_index);
        free((void *)tab->m_indxs);
      }

      if (tab->m_coord) free(tab->m_coord);
    }

    // Free memory allocated by tabset().
    if (tab->sense)   free(tab->sense);
    if (tab->p0)      free(tab->p0);
    if (tab->delta)   free(tab->delta);
    if (tab->extrema) free(tab->extrema);
  }

  tab->m_flag  = 0;
  tab->m_M     = 0;
  tab->m_N     = 0;
  tab->m_K     = 0x0;
  tab->m_map   = 0x0;
  tab->m_crval = 0x0;
  tab->m_index = 0x0;
  tab->m_indxs = 0x0;
  tab->m_coord = 0x0;

  tab->sense   = 0x0;
  tab->p0      = 0x0;
  tab->delta   = 0x0;
  tab->extrema = 0x0;
  tab->set_M   = 0;

  wcserr_clear(&(tab->err));

  tab->flag = 0;

  return 0;
}

//----------------------------------------------------------------------------

int tabsize(const struct tabprm *tab, int sizes[2])

{
  if (tab == 0x0) {
    sizes[0] = sizes[1] = 0;
    return 0;
  }

  // Base size, in bytes.
  sizes[0] = (int)sizeof(struct tabprm);

  // Total size of allocated memory, in bytes.
  sizes[1] = 0;

  int exsizes[2];
  int M = tab->M;

  // tabprm::K[];
  sizes[1] += M * (int)sizeof(int);

  // tabprm::map[];
  sizes[1] += M * (int)sizeof(int);

  // tabprm::crval[];
  sizes[1] += M * (int)sizeof(double);

  // tabprm::index[] and tabprm::m_indxs;
  sizes[1] += 2*M * (int)sizeof(double *);
  for (int m = 0; m < M; m++) {
    if (tab->index[m]) {
      sizes[1] += tab->K[m] * (int)sizeof(double);
    }
  }

  // tabprm::coord[];
  sizes[1] += M * tab->nc * (int)sizeof(double);

  // tab::err[].
  wcserr_size(tab->err, exsizes);
  sizes[1] += exsizes[0] + exsizes[1];

  // The remaining arrays are allocated by tabset().
  if (abs(tab->flag) != TABSET) {
    return 0;
  }

  // tabprm::sense[].
  if (tab->sense) {
    sizes[1] += M * (int)sizeof(int);
  }

  // tabprm::p0[].
  if (tab->p0) {
    sizes[1] += M * (int)sizeof(int);
  }

  // tabprm::delta[].
  if (tab->delta) {
    sizes[1] += M * (int)sizeof(double);
  }

  // tabprm::extrema[].
  int ne = (tab->nc / tab->K[0]) * 2 * M;
  sizes[1] += ne * (int)sizeof(double);

  return 0;
}

//----------------------------------------------------------------------------

int tabenq(const struct tabprm *tab, int enquiry)

{
  // Initialize.
  if (tab == 0x0) return TABERR_NULL_POINTER;

  int answer = 0;

  if (enquiry & TABENQ_MEM) {
    if (tab->m_flag != TABSET) return 0;
    answer = 1;
  }

  if (enquiry & TABENQ_SET) {
    if (abs(tab->flag) != TABSET) return 0;
    answer = 1;
  }

  if (enquiry & TABENQ_BYP) {
    if (tab->flag != 1 && tab->flag != -TABSET) return 0;
    answer = 1;
  }

  return answer;
}

//----------------------------------------------------------------------------

int tabprt(const struct tabprm *tab)

{
  char   text[128], *tpe = text + 128;
  double *dp;

  if (tab == 0x0) return TABERR_NULL_POINTER;

  if (abs(tab->flag) != TABSET) {
    wcsprintf("The tabprm struct is UNINITIALIZED.\n");
    return 0;
  }

  // Parameters supplied...
  wcsprintf("       flag: %d\n", tab->flag);
  wcsprintf("          M: %d\n", tab->M);

  // ...array dimensions.
  WCSPRINTF_PTR("          K: ", tab->K, "\n");
  wcsprintf("            ");
  for (int m = 0; m < tab->M; m++) {
    wcsprintf("%6d", tab->K[m]);
  }
  wcsprintf("\n");

  // ...map vector.
  WCSPRINTF_PTR("        map: ", tab->map, "\n");
  wcsprintf("            ");
  for (int m = 0; m < tab->M; m++) {
    wcsprintf("%6d", tab->map[m]);
  }
  wcsprintf("\n");

  // ...reference index value.
  WCSPRINTF_PTR("      crval: ", tab->crval, "\n");
  wcsprintf("            ");
  for (int m = 0; m < tab->M; m++) {
    wcsprintf("  %#- 11.5g", tab->crval[m]);
  }
  wcsprintf("\n");

  // ...index vectors.
  WCSPRINTF_PTR("      index: ", tab->index, "\n");

  if (tab->index != 0x0) {
    for (int m = 0; m < tab->M; m++) {
      wcsprintf("   index[%d]: ", m);
      WCSPRINTF_PTR("", tab->index[m], "");
      if (tab->index[m]) {
        for (int k = 0; k < tab->K[m]; k++) {
          if (k%5 == 0) {
            wcsprintf("\n            ");
          }
          wcsprintf("  %#- 11.5g", tab->index[m][k]);
        }
      }
      wcsprintf("\n");
    }
  }

  // ...coordinate array.
  WCSPRINTF_PTR("      coord: ", tab->coord, "\n");
  if ((dp = tab->coord)) {
    for (int n = 0; n < tab->nc; n++) {
      // Array index.
      int j = n;
      char *tp = text;
      *tp = '\0';
      for (int m = 0; m < tab->M; m++) {
        tp += strlen(tp);
        size_t tsize = tpe - tp;
        int nd = (tab->K[m] < 10) ? 1 : 2;
        snprintf(tp, tsize, ",%*d", nd, j % tab->K[m] + 1);
        j /= tab->K[m];
      }

      wcsprintf("             (*%s)", text);
      for (int m = 0; m < tab->M; m++) {
        wcsprintf("  %#- 11.5g", *(dp++));
      }
      wcsprintf("\n");
    }
  }

  // Derived values.
  wcsprintf("         nc: %d\n", tab->nc);

  WCSPRINTF_PTR("      sense: ", tab->sense, "\n");
  if (tab->sense) {
    wcsprintf("            ");
    for (int m = 0; m < tab->M; m++) {
      wcsprintf("%6d", tab->sense[m]);
    }
    wcsprintf("\n");
  }

  WCSPRINTF_PTR("         p0: ", tab->p0, "\n");
  if (tab->p0) {
    wcsprintf("            ");
    for (int m = 0; m < tab->M; m++) {
      wcsprintf("%6d", tab->p0[m]);
    }
    wcsprintf("\n");
  }

  WCSPRINTF_PTR("      delta: ", tab->delta, "\n");
  if (tab->delta) {
    wcsprintf("            ");
    for (int m = 0; m < tab->M; m++) {
      wcsprintf("  %#- 11.5g", tab->delta[m]);
    }
    wcsprintf("\n");
  }

  WCSPRINTF_PTR("    extrema: ", tab->extrema, "\n");
  if ((dp = tab->extrema)) {
    for (int n = 0; n < tab->nc/tab->K[0]; n++) {
      // Array index.
      int j = n;
      char *tp = text;
      *tp = '\0';
      for (int m = 1; m < tab->M; m++) {
        tp += strlen(tp);
        size_t tsize = tpe - tp;
        int nd = (tab->K[m] < 10) ? 1 : 2;
        snprintf(tp, tsize, ",%*d", nd, j % tab->K[m] + 1);
        j /= tab->K[m];
      }

      wcsprintf("             (*,*%s)", text);
      for (int m = 0; m < 2*tab->M; m++) {
        if (m == tab->M) wcsprintf("->  ");
        wcsprintf("  %#- 11.5g", *(dp++));
      }
      wcsprintf("\n");
    }
  }

  // Error handling.
  WCSPRINTF_PTR("        err: ", tab->err, "\n");
  if (tab->err) {
    wcserr_prt(tab->err, "             ");
  }

  // Memory management.
  wcsprintf("     m_flag: %d\n", tab->m_flag);
  wcsprintf("        m_M: %d\n", tab->m_M);
  wcsprintf("        m_N: %d\n", tab->m_N);

  WCSPRINTF_PTR("        m_K: ", tab->m_K, "");
  if (tab->m_K == tab->K) wcsprintf("  (= K)");
  wcsprintf("\n");

  WCSPRINTF_PTR("      m_map: ", tab->m_map, "");
  if (tab->m_map == tab->map) wcsprintf("  (= map)");
  wcsprintf("\n");

  WCSPRINTF_PTR("    m_crval: ", tab->m_crval, "");
  if (tab->m_crval == tab->crval) wcsprintf("  (= crval)");
  wcsprintf("\n");

  WCSPRINTF_PTR("    m_index: ", tab->m_index, "");
  if (tab->m_index == tab->index) wcsprintf("  (= index)");
  wcsprintf("\n");
  for (int m = 0; m < tab->M; m++) {
    wcsprintf(" m_indxs[%d]: ", m);
    WCSPRINTF_PTR("", tab->m_indxs[m], "");
    if (tab->m_indxs[m] == tab->index[m]) wcsprintf("  (= index[%d])", m);
    wcsprintf("\n");
  }

  WCSPRINTF_PTR("    m_coord: ", tab->m_coord, "");
  if (tab->m_coord == tab->coord) wcsprintf("  (= coord)");
  wcsprintf("\n");

  return 0;
}

//----------------------------------------------------------------------------

int tabperr(const struct tabprm *tab, const char *prefix)

{
  if (tab == 0x0) return TABERR_NULL_POINTER;

  if (tab->err) {
    wcserr_prt(tab->err, prefix);
  }

  return 0;
}

//----------------------------------------------------------------------------

int tabset(struct tabprm *tab)

{
  static const char *function = "tabset";

  if (tab == 0x0) return TABERR_NULL_POINTER;
  if (tab->flag == -TABSET) return 0;
  struct wcserr **err = &(tab->err);

  // Check the number of tabular coordinate axes.
  int M = tab->M;
  if (M < 1) {
    return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
      "Invalid tabular parameters: M must be positive, got %d", M);
  }

  // Check the axis lengths.
  if (!tab->K) {
    return wcserr_set(WCSERR_SET(TABERR_MEMORY),
      "Null pointers in tabprm struct");
  }

  tab->nc = 1;
  for (int m = 0; m < M; m++) {
    if (tab->K[m] < 1) {
      return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
        "Invalid tabular parameters: Each element of K must be positive, "
        "got %d", tab->K[m]);
    }

    // Number of coordinate vectors in the coordinate array.
    tab->nc *= tab->K[m];
  }

  // Check that the map vector is sensible.
  if (!tab->map) {
    return wcserr_set(WCSERR_SET(TABERR_MEMORY),
      "Null pointers in tabprm struct");
  }

  for (int m = 0; m < M; m++) {
    int i = tab->map[m];
    if (i < 0) {
      return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
        "Invalid tabular parameters: Each element of map must be "
        "non-negative, got %d", i);
    }
  }

  // Check memory allocation for the remaining vectors.
  if (!tab->crval || !tab->index || !tab->coord) {
    return wcserr_set(WCSERR_SET(TABERR_MEMORY),
      "Null pointers in tabprm struct");
  }

  // Take memory if signalled to by wcstab().
  for (int m = 0; m < tab->m_M; m++) {
    if (tab->m_indxs[m] == (double *)0x1 &&
       (tab->m_indxs[m] = tab->index[m])) {
      tab->m_flag = TABSET;
    }
  }

  if (tab->m_coord == (double *)0x1 &&
     (tab->m_coord = tab->coord)) {
    tab->m_flag = TABSET;
  }


  // Allocate memory for work vectors.
  if (abs(tab->flag) != TABSET || tab->set_M < M) {
    // Free memory that may have been allocated previously.
    if (tab->sense)   free(tab->sense);
    if (tab->p0)      free(tab->p0);
    if (tab->delta)   free(tab->delta);
    if (tab->extrema) free(tab->extrema);

    tab->sense   = 0x0;
    tab->p0      = 0x0;
    tab->delta   = 0x0;
    tab->extrema = 0x0;

    // Allocate memory for internal arrays.
    if (!(tab->sense = calloc(M, sizeof(int)))) {
      return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
    }

    if (!(tab->p0 = calloc(M, sizeof(int)))) {
      free(tab->sense);
      return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
    }

    if (!(tab->delta = calloc(M, sizeof(double)))) {
      free(tab->sense);
      free(tab->p0);
      return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
    }

    int ne = (tab->nc / tab->K[0]) * 2 * M;
    if (!(tab->extrema = calloc(ne, sizeof(double)))) {
      free(tab->sense);
      free(tab->p0);
      free(tab->delta);
      return wcserr_set(TAB_ERRMSG(TABERR_MEMORY));
    }

    tab->set_M = M;
  }

  // Check that the index vectors are monotonic.
  int *Km = tab->K;
  for (int m = 0; m < M; m++, Km++) {
    tab->sense[m] = 0;

    if (*Km > 1) {
      double *Psi;
      if ((Psi = tab->index[m]) == 0x0) {
        // Default indexing.
        tab->sense[m] = 1;

      } else {
        for (int k = 0; k < *Km-1; k++) {
          switch (tab->sense[m]) {
          case 0:
            if (Psi[k] < Psi[k+1]) {
              // Monotonic increasing.
              tab->sense[m] = 1;
            } else if (Psi[k] > Psi[k+1]) {
              // Monotonic decreasing.
              tab->sense[m] = -1;
            }
            break;

          case 1:
            if (Psi[k] > Psi[k+1]) {
              // Should be monotonic increasing.
              free(tab->sense);
              free(tab->p0);
              free(tab->delta);
              free(tab->extrema);
              return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
                "Invalid tabular parameters: Index vectors are not "
                "monotonically increasing");
            }
            break;

          case -1:
            if (Psi[k] < Psi[k+1]) {
              // Should be monotonic decreasing.
              free(tab->sense);
              free(tab->p0);
              free(tab->delta);
              free(tab->extrema);
              return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
                "Invalid tabular parameters: Index vectors are not "
                "monotonically decreasing");
            }
            break;
          default:
            // Not possible.
            break;
          }
        }
      }

      if (tab->sense[m] == 0) {
        free(tab->sense);
        free(tab->p0);
        free(tab->delta);
        free(tab->extrema);
        return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
          "Invalid tabular parameters: Index vectors are not monotonic");
      }
    }
  }

  // Find the extremal values of the coordinate elements in each row.
  double *dcrd = tab->coord;
  double *dmin = tab->extrema;
  double *dmax = tab->extrema + M;
  for (int ic = 0; ic < tab->nc; ic += tab->K[0]) {
    for (int m = 0; m < M; m++, dcrd++) {
      if (tab->K[0] > 1) {
        // Extrapolate a little before the start of the row.
        double dPsi;
        double *Psi = tab->index[0];
        if (Psi == 0x0) {
          dPsi = 1.0;
        } else {
          dPsi = Psi[1] - Psi[0];
        }

        double dval = *dcrd;
        if (dPsi != 0.0) {
          dval -= 0.5 * (*(dcrd+M) - *dcrd)/dPsi;
        }

        *(dmax+m) = *(dmin+m) = dval;
      } else {
        *(dmax+m) = *(dmin+m) = *dcrd;
      }
    }

    dcrd -= M;
    for (int i = 0; i < tab->K[0]; i++) {
      for (int m = 0; m < M; m++, dcrd++) {
        if (*(dmax+m) < *dcrd) *(dmax+m) = *dcrd;
        if (*(dmin+m) > *dcrd) *(dmin+m) = *dcrd;

        if (tab->K[0] > 1 && i == tab->K[0]-1) {
          // Extrapolate a little beyond the end of the row.
          double dPsi;
          double *Psi = tab->index[0];
          if (Psi == 0x0) {
            dPsi = 1.0;
          } else {
            dPsi = Psi[i] - Psi[i-1];
          }

          double dval = *dcrd;
          if (dPsi != 0.0) {
            dval += 0.5 * (*dcrd - *(dcrd-M))/dPsi;
          }

          if (*(dmax+m) < dval) *(dmax+m) = dval;
          if (*(dmin+m) > dval) *(dmin+m) = dval;
        }
      }
    }

    dmin += (ptrdiff_t)(2*M);
    dmax += (ptrdiff_t)(2*M);
  }

  tab->flag = (tab->flag == 1) ? -TABSET : TABSET;

  return 0;
}

//----------------------------------------------------------------------------

int tabx2s(
  struct tabprm *tab,
  int ncoord,
  int nelem,
  const double x[],
  double world[],
  int stat[])

{
  static const char *function = "tabx2s";

  int status;

  if (tab == 0x0) return TABERR_NULL_POINTER;
  struct wcserr **err = &(tab->err);

  // Initialize if required.
  if (abs(tab->flag) != TABSET) {
    if ((status = tabset(tab))) return status;
  }

  // This is used a lot.
  int M = tab->M;

  status = 0;
  const double *xp = x;
  double *wp = world;
  int *statp = stat;
  for (int n = 0; n < ncoord; n++) {
    // Determine the indexes.
    int *Km = tab->K;
    for (int m = 0; m < M; m++, Km++) {
      // N.B. psi_m and Upsilon_m are 1-relative FITS indexes.
      int i = tab->map[m];
      double psi_m = *(xp+i) + tab->crval[m];

      double *Psi = tab->index[m];
      double upsilon;
      if (Psi == 0x0) {
        // Default indexing is simple.
        upsilon = psi_m;

      } else {
        // To ease confusion, decrement Psi so that we can use 1-relative
        // C array indexing to match the 1-relative FITS indexing.
        Psi--;

        if (*Km == 1) {
          // Index vector is degenerate.
          if (Psi[1]-0.5 <= psi_m && psi_m <= Psi[1]+0.5) {
            upsilon = psi_m;
          } else {
            *statp = 1;
            status = wcserr_set(TAB_ERRMSG(TABERR_BAD_X));
            goto next;
          }

        } else {
          // Interpolate in the indexing vector.
	  int k;
          if (tab->sense[m] == 1) {
            // Monotonic increasing index values.
            if (psi_m < Psi[1]) {
              if (Psi[1] - 0.5*(Psi[2]-Psi[1]) <= psi_m) {
                // Allow minor extrapolation.
                k = 1;

              } else {
                // Index is out of range.
                *statp = 1;
                status = wcserr_set(TAB_ERRMSG(TABERR_BAD_X));
                goto next;
              }

            } else if (Psi[*Km] < psi_m) {
              if (psi_m <= Psi[*Km] + 0.5*(Psi[*Km]-Psi[*Km-1])) {
                // Allow minor extrapolation.
                k = *Km - 1;

              } else {
                // Index is out of range.
                *statp = 1;
                status = wcserr_set(TAB_ERRMSG(TABERR_BAD_X));
                goto next;
              }

            } else {
              for (k = 1; k < *Km; k++) {
                if (psi_m < Psi[k]) {
                  continue;
                }
                if (Psi[k] == psi_m && psi_m < Psi[k+1]) {
                  break;
                }
                if (Psi[k] < psi_m && psi_m <= Psi[k+1]) {
                  break;
                }
              }
            }

          } else {
            // Monotonic decreasing index values.
            if (psi_m > Psi[1]) {
              if (Psi[1] + 0.5*(Psi[1]-Psi[2]) >= psi_m) {
                // Allow minor extrapolation.
                k = 1;

              } else {
                // Index is out of range.
                *statp = 1;
                status = wcserr_set(TAB_ERRMSG(TABERR_BAD_X));
                goto next;
              }

            } else if (psi_m < Psi[*Km]) {
              if (Psi[*Km] - 0.5*(Psi[*Km-1]-Psi[*Km]) <= psi_m) {
                // Allow minor extrapolation.
                k = *Km - 1;

              } else {
                // Index is out of range.
                *statp = 1;
                status = wcserr_set(TAB_ERRMSG(TABERR_BAD_X));
                goto next;
              }

            } else {
              for (k = 1; k < *Km; k++) {
                if (psi_m > Psi[k]) {
                  continue;
                }
                if (Psi[k] == psi_m && psi_m > Psi[k+1]) {
                  break;
                }
                if (Psi[k] > psi_m && psi_m >= Psi[k+1]) {
                  break;
                }
              }
            }
          }

          upsilon = k + (psi_m - Psi[k]) / (Psi[k+1] - Psi[k]);
        }
      }

      if (upsilon < 0.5 || upsilon > *Km + 0.5) {
        // Index out of range.
        *statp = 1;
        status = wcserr_set(TAB_ERRMSG(TABERR_BAD_X));
        goto next;
      }

      // Fiducial array indices and fractional offset.
      // p1 is 1-relative while tab::p0 is 0-relative.
      int p1 = (int)floor(upsilon);
      tab->p0[m] = p1 - 1;
      tab->delta[m] = upsilon - p1;

      if (p1 == 0) {
        // Extrapolation below p1 == 1.
        tab->p0[m] += 1;
        tab->delta[m] -= 1.0;
      } else if (p1 == *Km && *Km > 1) {
        // Extrapolation above p1 == K_m.
        tab->p0[m] -= 1;
        tab->delta[m] += 1.0;
      }
    }


    // Now interpolate in the coordinate array; the M-dimensional linear
    // interpolation algorithm is described in Sect. 3.4 of WCS Paper IV.
    for (int m = 0; m < M; m++) {
      int i = tab->map[m];
      *(wp+i) = 0.0;
    }

    // Loop over the 2^M vertices surrounding P.
    int nv = 1 << M;
    for (int iv = 0; iv < nv; iv++) {
      // Locate vertex in the coordinate array and compute its weight.
      ptrdiff_t offset = 0;
      double wgt = 1.0;
      for (int m = M-1; m >= 0; m--) {
        offset *= tab->K[m];
        offset += tab->p0[m];
        if (iv & (1 << m)) {
          if (tab->K[m] > 1) offset++;
          wgt *= tab->delta[m];
        } else {
          wgt *= 1.0 - tab->delta[m];
        }
      }

      if (wgt == 0.0) continue;

      // Add the contribution from this vertex to each element.
      double *coord = tab->coord + offset*M;
      for (int m = 0; m < M; m++) {
        int i = tab->map[m];
        *(wp+i) += *(coord++) * wgt;
      }

      if (wgt == 1.0) break;
    }

    *statp = 0;

next:
    xp += nelem;
    wp += nelem;
    statp++;
  }

  return status;
}

//----------------------------------------------------------------------------

// Helper functions used only by tabs2x().
static int tabedge(struct tabprm *);
static int tabrow(struct tabprm *, const double *);
static int tabvox(struct tabprm *, const double *, int, double **,
                  unsigned int *);

int tabs2x(
  struct tabprm* tab,
  int ncoord,
  int nelem,
  const double world[],
  double x[],
  int stat[])

{
  static const char *function = "tabs2x";

  int status;

  if (tab == 0x0) return TABERR_NULL_POINTER;
  struct wcserr **err = &(tab->err);

  // Initialize if required.
  if (abs(tab->flag) != TABSET) {
    if ((status = tabset(tab))) return status;
  }

  // This is used a lot.
  int M = tab->M;
  if (M < 1) {
    // Won't get past tabset(), balm for static code analysers.
    return wcserr_set(WCSERR_SET(TABERR_BAD_PARAMS),
      "Invalid tabular parameters: M must be positive, got %d", M);
  }

  double **tabcoord = 0x0;
  int nv = 0;
  if (1 < M) {
    nv = 1 << M;
    tabcoord = (double **)calloc(nv, sizeof(double *));
  }


  status = 0;
  const double *wp = world;
  double *xp = x;
  int *statp = stat;
  for (int n = 0; n < ncoord; n++) {
    // Locate this coordinate in the coordinate array.
    int edge = 0;
    for (int m = 0; m < M; m++) {
      tab->p0[m] = 0;
    }

    int ic;
    for (ic = 0; ic < tab->nc; ic++) {
      if (tab->p0[0] == 0) {
        // New row, could it contain a solution?
        if (edge || tabrow(tab, wp)) {
          // No, skip it.
          ic += tab->K[0];
          if (1 < M) {
            tab->p0[1]++;
            edge = tabedge(tab);
          }

          // Because ic will be incremented when the loop is reentered.
          ic--;
          continue;
        }
      }

      if (M == 1) {
        // Deal with the one-dimensional case separately for efficiency.
        double w = wp[tab->map[0]];
        if (w == tab->coord[0]) {
          tab->p0[0] = 0;
          tab->delta[0] = 0.0;
          break;

        } else if (ic < tab->nc - 1) {
          if (((tab->coord[ic] <= w && w <= tab->coord[ic+1]) ||
               (tab->coord[ic] >= w && w >= tab->coord[ic+1])) &&
               (tab->index[0] == 0x0 ||
                tab->index[0][ic] != tab->index[0][ic+1])) {
            tab->p0[0] = ic;
            tab->delta[0] = (w - tab->coord[ic]) /
                            (tab->coord[ic+1] - tab->coord[ic]);
            break;
          }
        }

      } else {
        // Multi-dimensional tables are harder.
        if (!edge) {
          // Addresses of the coordinates for each corner of the "voxel".
          for (int iv = 0; iv < nv; iv++) {
            ptrdiff_t offset = 0;
            for (int m = M-1; m >= 0; m--) {
              offset *= tab->K[m];
              offset += tab->p0[m];
              if ((iv & (1 << m)) && (tab->K[m] > 1)) offset++;
            }
            tabcoord[iv] = tab->coord + offset*M;
          }

          if (tabvox(tab, wp, 0, tabcoord, 0x0) == 0) {
            // Found a solution.
            break;
          }
        }

        // Next voxel.
        tab->p0[0]++;
        edge = tabedge(tab);
      }
    }


    if (ic == tab->nc) {
      // Coordinate not found; allow minor extrapolation.
      if (M == 1) {
        // Should there be a solution?
        double w = wp[tab->map[0]];
        if (tab->extrema[0] <= w && w <= tab->extrema[1]) {
          double *dcrd = tab->coord;
          for (int i = 0; i < 2; i++) {
            if (i) dcrd += tab->K[0] - 2;

            double delta = (w - *dcrd) / (*(dcrd+1) - *dcrd);

            if (i == 0) {
              if (-0.5 <= delta && delta <= 0.0) {
                tab->p0[0] = 0;
                tab->delta[0] = delta;
                ic = 0;
                break;
              }
            } else {
              if (1.0 <= delta && delta <= 1.5) {
                tab->p0[0] = tab->K[0] - 1;
                tab->delta[0] = delta - 1.0;
                ic = 0;
              }
            }
          }
        }

      } else {
        // Multi-dimensional tables.
        // >>> TBD <<<
      }
    }


    if (ic == tab->nc) {
      // Coordinate not found.
      *statp = 1;
      status = wcserr_set(TAB_ERRMSG(TABERR_BAD_WORLD));

    } else {
      // Determine the intermediate world coordinates.
      int *Km = tab->K;
      for (int m = 0; m < M; m++, Km++) {
        // N.B. Upsilon_m and psi_m are 1-relative FITS indexes.
        double upsilon = (tab->p0[m] + 1) + tab->delta[m];

        if (upsilon < 0.5 || upsilon > *Km + 0.5) {
          // Index out of range.
          *statp = 1;
          status = wcserr_set(TAB_ERRMSG(TABERR_BAD_WORLD));

        } else {
          // Do inverse lookup of the index vector.
          double *Psi = tab->index[m];
          double psi_m;
          if (Psi == 0x0) {
            // Default indexing.
            psi_m = upsilon;

          } else {
            // Decrement Psi and use 1-relative C array indexing to match the
            // 1-relative FITS indexing.
            Psi--;

            if (*Km == 1) {
              // Degenerate index vector.
              psi_m = Psi[1];
            } else {
              int k = (int)(upsilon);
              psi_m = Psi[k];
              if (k < *Km) {
                psi_m += (upsilon - k) * (Psi[k+1] - Psi[k]);
              }
            }
          }

          xp[tab->map[m]] = psi_m - tab->crval[m];
        }
      }
      *statp = 0;
    }

    wp += nelem;
    xp += nelem;
    statp++;
  }

  if (tabcoord) free((void *)tabcoord);

  return status;
}

/*----------------------------------------------------------------------------
* Convenience routine to check whether tabprm::p0 has been incremented beyond
* the end of an index vector and if so move it to the start of the next one.
* Returns 1 if tabprm::p0 is sitting at the end of any non-degenerate index
* vector.
*---------------------------------------------------------------------------*/

int tabedge(struct tabprm* tab)

{
  int edge = 0;

  for (int m = 0; m < tab->M; m++) {
    if (tab->p0[m] == tab->K[m]) {
      // p0 has been incremented beyond the end of an index vector, point it
      // to the next one.
      tab->p0[m] = 0;
      if (m < tab->M-1) {
        tab->p0[m+1]++;
      }
    } else if (tab->p0[m] == tab->K[m]-1 && tab->K[m] > 1) {
      // p0 is sitting at the end of a non-degenerate index vector.
      edge = 1;
    }
  }

  return edge;
}

/*----------------------------------------------------------------------------
* Quick test to see whether the world coordinate indicated by wp could lie
* somewhere along (or near) the row of the image indexed by tabprm::p0.
* Return 0 if so, 1 otherwise.
*
* tabprm::p0 selects a particular row of the image, p0[0] being ignored (i.e.
* treated as zero).  Adjacent rows that delimit a row of "voxels" are formed
* by incrementing elements other than p0[0] in all binary combinations.  N.B.
* these are not the same as the voxels (pixels) that are indexed by, and
* centred on, integral pixel coordinates in FITS.
*
* To see why it is necessary to examine the adjacent rows, consider the 2-D
* case where the first world coordinate element is constant along each row.
* If the first element of wp has value 0.5, and its value in the row indexed
* by p0 has value 0, and in the next row it has value 1, then it is clear that
* the solution lies in neither row but somewhere between them.  Thus both rows
* will be involved in finding the solution.
*
* tabprm::extrema is the address of the first element of a 1-D array that
* records the minimum and maximum value of each element of the coordinate
* vector in each row of the coordinate array, treated as though it were
* defined as
*
*   double extrema[K_M]...[K_2][2][M]
*
* The minimum is recorded in the first element of the compressed K_1
* dimension, then the maximum.
*---------------------------------------------------------------------------*/

int tabrow(struct tabprm* tab, const double *wp)

{
  const double tol = 1e-10;

  int M = tab->M;

  // The number of corners in a "voxel".  We need examine only half this
  // number of rows.  The extra factor of two will be used to select between
  // the minimal and maximal values in each row.
  unsigned int nv = 1 << M;

  unsigned int eq = 0;
  unsigned int lt = 0;
  unsigned int gt = 0;
  for (unsigned int iv = 0; iv < nv; iv++) {
    // Find the index into tabprm::extrema for this row.
    int offset = 0;
    for (int m = M-1; m > 0; m--) {
      offset *= tab->K[m];
      offset += tab->p0[m];

      // Select the row.
      if (iv & (1 << m)) {
        if (tab->K[m] > 1) offset++;
      }
    }

    // The K_1 dimension has length 2 (see prologue).
    offset *= 2;

    // Select the minimum on even numbered iterations, else the maximum.
    if (iv & 1) offset++;

    // The last dimension has length M (see prologue).
    offset *= M;

    // Address of the extremal elements (min or max) for this row.
    double *cp = tab->extrema + offset;

    // For each coordinate element, we only need to find one row where its
    // minimum value is less than that of wp, and one row where the maximum
    // value is greater.  That doesn't mean that there is a solution, only
    // that there might be.
    for (int m = 0; m < M; m++, cp++) {
      // Apply the axis mapping.
      double w = wp[tab->map[m]];

      // Finally the test itself; set bits in the bitmask.
      if (fabs(*cp - w) < tol) {
        eq |= (1 << m);
      } else if (*cp < w) {
        lt |= (1 << m);
      } else if (*cp > w) {
        gt |= (1 << m);
      }
    }

    // Have all bits been switched on?
    if ((lt | eq) == nv-1 && (gt | eq) == nv-1) {
      // A solution could lie within this row of voxels.
      return 0;
    }
  }

  // No solution in this row.
  return 1;
}

/*----------------------------------------------------------------------------
* Does the world coordinate indicated by wp lie within the voxel indexed by
* tabprm::p0?  If so, do a binary chop of the interior of the voxel to find
* it and return 0, with tabprm::delta set to the solution.  Else return 1.
*
* As in tabrow(), a "voxel" is formed by incrementing the elements of
* tabprm::p0 in all binary combinations.  Note that these are not the same as
* the voxels (pixels) that are indexed by, and centred on, integral pixel
* coordinates in FITS.
*
* tabvox() calls itself recursively.  When called from outside, level, being
* the level of recursion, should be given as zero.  tabcoord is an array
* holding the addresses of the coordinates for each corner of the voxel.
* vox is the address of a work array (vox2) used during recursive calls to
* dissect the voxel.  It is ignored when tabvox() is called from outside
* (level == 0).
*
* It is assumed that the image dimensions are no greater than 32.
----------------------------------------------------------------------------*/

int tabvox(
  struct tabprm* tab,
  const double *wp,
  int level,
  double **tabcoord,
  unsigned int *vox)

{
  const double tol = 1e-10;

  int M = tab->M;

  // The number of corners in a voxel.
  unsigned int nv = 1 << M;

  double dv = 1.0;
  for (int i = 0; i < level; i++) {
    dv /= 2.0;
  }

  // Could the coordinate lie within this voxel (level == 0) or sub-voxel
  // (level > 0)?  We use the fact that with linear interpolation the
  // coordinate elements are extremal in a corner and test each one.
  unsigned int lt = 0;
  unsigned int gt = 0;
  unsigned int eq = 0;
  for (unsigned int iv = 0; iv < nv; iv++) {
    // Select a corner of the sub-voxel.
    double coord[32];
    for (int m = 0; m < M; m++) {
      coord[m] = 0.0;
      tab->delta[m] = level ? dv*vox[m] : 0.0;

      if (iv & (1 << m)) {
        tab->delta[m] += dv;
      }
    }

    // Compute the coordinates of this corner of the sub-voxel by linear
    // interpolation using the weighting algorithm described in Sect. 3.4 of
    // WCS Paper IV.
    for (unsigned int jv = 0; jv < nv; jv++) {
      // Find the weight for this corner of the parent voxel.
      double wgt = 1.0;
      for (int m = 0; m < M; m++) {
        if (jv & (1 << m)) {
          wgt *= tab->delta[m];
        } else {
          wgt *= 1.0 - tab->delta[m];
        }
      }

      if (wgt == 0.0) continue;

      // Add its contribution to each coordinate element.
      double *cp = tabcoord[jv];
      for (int m = 0; m < M; m++) {
        coord[m] += *(cp++) * wgt;
      }

      if (wgt == 1.0) break;
    }

    // Coordinate elements are minimal or maximal in a corner.
    unsigned int et = 0;
    for (int m = 0; m < M; m++) {
      // Apply the axis mapping.
      double w = wp[tab->map[m]];

      // Finally the test itself; set bits in the bitmask.
      if (fabs(coord[m] - w) < tol) {
        et |= (1 << m);
      } else if (coord[m] < w) {
        lt |= (1 << m);
      } else if (coord[m] > w) {
        gt |= (1 << m);
      }
    }

    if (et == nv-1) {
      // We've stumbled across a solution in this corner of the sub-voxel.
      return 0;
    }

    eq |= et;
  }

  // Could the coordinate lie within this sub-voxel?
  if ((lt | eq) == nv-1 && (gt | eq) == nv-1) {
    // Yes it could, but does it?

    // Is it time to stop the recursion?
    if (level == 31) {
      // We have a solution, squeeze out the last bit of juice.
      dv /= 2.0;
      for (int m = 0; m < M; m++) {
        tab->delta[m] = dv * (2.0*vox[m] + 1.0);
      }

      return 0;
    }

    // Subdivide the sub-voxel and try again for each subdivision.
    for (unsigned int iv = 0; iv < nv; iv++) {
      // Select the subdivision.
      unsigned int vox2[32];
      for (int m = 0; m < M; m++) {
        vox2[m] = level ? 2*vox[m] : 0;
        if (iv & (1 << m)) {
          vox2[m]++;
        }
      }

      // Recurse.
      if (tabvox(tab, wp, level+1, tabcoord, vox2) == 0) {
        return 0;
      }
    }
  }

  // No solution in this sub-voxel.
  return 1;
}
