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arrayutils.c
/*-------------------------------------------------------------------------
 *
 * arrayutils.c
 *      This file contains some support routines required for array functions.
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/utils/adt/arrayutils.c,v 1.27 2009/01/01 17:23:49 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "catalog/pg_type.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/memutils.h"


/*
 * Convert subscript list into linear element number (from 0)
 *
 * We assume caller has already range-checked the dimensions and subscripts,
 * so no overflow is possible.
 */
int
ArrayGetOffset(int n, const int *dim, const int *lb, const int *indx)
{
      int               i,
                        scale = 1,
                        offset = 0;

      for (i = n - 1; i >= 0; i--)
      {
            offset += (indx[i] - lb[i]) * scale;
            scale *= dim[i];
      }
      return offset;
}

/*
 * Same, but subscripts are assumed 0-based, and use a scale array
 * instead of raw dimension data (see mda_get_prod to create scale array)
 */
int
ArrayGetOffset0(int n, const int *tup, const int *scale)
{
      int               i,
                        lin = 0;

      for (i = 0; i < n; i++)
            lin += tup[i] * scale[i];
      return lin;
}

/*
 * Convert array dimensions into number of elements
 *
 * This must do overflow checking, since it is used to validate that a user
 * dimensionality request doesn't overflow what we can handle.
 *
 * We limit array sizes to at most about a quarter billion elements,
 * so that it's not necessary to check for overflow in quite so many
 * places --- for instance when palloc'ing Datum arrays.
 *
 * The multiplication overflow check only works on machines that have int64
 * arithmetic, but that is nearly all platforms these days, and doing check
 * divides for those that don't seems way too expensive.
 */
int
ArrayGetNItems(int ndim, const int *dims)
{
      int32       ret;
      int               i;

#define MaxArraySize ((Size) (MaxAllocSize / sizeof(Datum)))

      if (ndim <= 0)
            return 0;
      ret = 1;
      for (i = 0; i < ndim; i++)
      {
            int64       prod;

            /* A negative dimension implies that UB-LB overflowed ... */
            if (dims[i] < 0)
                  ereport(ERROR,
                              (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                               errmsg("array size exceeds the maximum allowed (%d)",
                                          (int) MaxArraySize)));

            prod = (int64) ret *(int64) dims[i];

            ret = (int32) prod;
            if ((int64) ret != prod)
                  ereport(ERROR,
                              (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                               errmsg("array size exceeds the maximum allowed (%d)",
                                          (int) MaxArraySize)));
      }
      Assert(ret >= 0);
      if ((Size) ret > MaxArraySize)
            ereport(ERROR,
                        (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                         errmsg("array size exceeds the maximum allowed (%d)",
                                    (int) MaxArraySize)));
      return (int) ret;
}

/*
 * Compute ranges (sub-array dimensions) for an array slice
 *
 * We assume caller has validated slice endpoints, so overflow is impossible
 */
void
mda_get_range(int n, int *span, const int *st, const int *endp)
{
      int               i;

      for (i = 0; i < n; i++)
            span[i] = endp[i] - st[i] + 1;
}

/*
 * Compute products of array dimensions, ie, scale factors for subscripts
 *
 * We assume caller has validated dimensions, so overflow is impossible
 */
void
mda_get_prod(int n, const int *range, int *prod)
{
      int               i;

      prod[n - 1] = 1;
      for (i = n - 2; i >= 0; i--)
            prod[i] = prod[i + 1] * range[i + 1];
}

/*
 * From products of whole-array dimensions and spans of a sub-array,
 * compute offset distances needed to step through subarray within array
 *
 * We assume caller has validated dimensions, so overflow is impossible
 */
void
mda_get_offset_values(int n, int *dist, const int *prod, const int *span)
{
      int               i,
                        j;

      dist[n - 1] = 0;
      for (j = n - 2; j >= 0; j--)
      {
            dist[j] = prod[j] - 1;
            for (i = j + 1; i < n; i++)
                  dist[j] -= (span[i] - 1) * prod[i];
      }
}

/*
 * Generates the tuple that is lexicographically one greater than the current
 * n-tuple in "curr", with the restriction that the i-th element of "curr" is
 * less than the i-th element of "span".
 *
 * Returns -1 if no next tuple exists, else the subscript position (0..n-1)
 * corresponding to the dimension to advance along.
 *
 * We assume caller has validated dimensions, so overflow is impossible
 */
int
mda_next_tuple(int n, int *curr, const int *span)
{
      int               i;

      if (n <= 0)
            return -1;

      curr[n - 1] = (curr[n - 1] + 1) % span[n - 1];
      for (i = n - 1; i && curr[i] == 0; i--)
            curr[i - 1] = (curr[i - 1] + 1) % span[i - 1];

      if (i)
            return i;
      if (curr[0])
            return 0;

      return -1;
}

/*
 * ArrayGetIntegerTypmods: verify that argument is a 1-D cstring array,
 * and get the contents converted to integers.  Returns a palloc'd array
 * and places the length at *n.
 */
int32 *
ArrayGetIntegerTypmods(ArrayType *arr, int *n)
{
      int32    *result;
      Datum    *elem_values;
      int               i;

      if (ARR_ELEMTYPE(arr) != CSTRINGOID)
            ereport(ERROR,
                        (errcode(ERRCODE_ARRAY_ELEMENT_ERROR),
                         errmsg("typmod array must be type cstring[]")));

      if (ARR_NDIM(arr) != 1)
            ereport(ERROR,
                        (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                         errmsg("typmod array must be one-dimensional")));

      if (ARR_HASNULL(arr))
            ereport(ERROR,
                        (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                         errmsg("typmod array must not contain nulls")));

      /* hardwired knowledge about cstring's representation details here */
      deconstruct_array(arr, CSTRINGOID,
                                -2, false, 'c',
                                &elem_values, NULL, n);

      result = (int32 *) palloc(*n * sizeof(int32));

      for (i = 0; i < *n; i++)
            result[i] = pg_atoi(DatumGetCString(elem_values[i]),
                                          sizeof(int32), '\0');

      pfree(elem_values);

      return result;
}

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