src/include/utils/arrayaccess.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * arrayaccess.h
   4  *        Declarations for element-by-element access to Postgres arrays.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/utils/arrayaccess.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef ARRAYACCESS_H
  15 #define ARRAYACCESS_H
  16
  17 #include "access/tupmacs.h"
  18 #include "utils/array.h"
  19
  20
  21 /*
  22  * Functions for iterating through elements of a flat or expanded array.
  23  * These require a state struct "array_iter iter".
  24  *
  25  * Use "array_iter_setup(&iter, arrayptr);" to prepare to iterate, and
  26  * "datumvar = array_iter_next(&iter, &isnullvar, index, ...);" to fetch
  27  * the next element into datumvar/isnullvar.
  28  * "index" must be the zero-origin element number; we make caller provide
  29  * this since caller is generally counting the elements anyway.  Despite
  30  * that, these functions can only fetch elements sequentially.
  31  */
  32
  33 typedef struct array_iter
  34 {
  35         /* datumptr being NULL or not tells if we have flat or expanded array */
  36
  37         /* Fields used when we have an expanded array */
  38         Datum      *datumptr;           /* Pointer to Datum array */
  39         bool       *isnullptr;          /* Pointer to isnull array */
  40
  41         /* Fields used when we have a flat array */
  42         char       *dataptr;            /* Current spot in the data area */
  43         bits8      *bitmapptr;          /* Current byte of the nulls bitmap, or NULL */
  44         int                     bitmask;                /* mask for current bit in nulls bitmap */
  45 } array_iter;
  46
  47
  48 static inline void
  49 array_iter_setup(array_iter *it, AnyArrayType *a)
  50 {
  51         if (VARATT_IS_EXPANDED_HEADER(a))
  52         {
  53                 if (a->xpn.dvalues)
  54                 {
  55                         it->datumptr = a->xpn.dvalues;
  56                         it->isnullptr = a->xpn.dnulls;
  57                         /* we must fill all fields to prevent compiler warnings */
  58                         it->dataptr = NULL;
  59                         it->bitmapptr = NULL;
  60                 }
  61                 else
  62                 {
  63                         /* Work with flat array embedded in the expanded datum */
  64                         it->datumptr = NULL;
  65                         it->isnullptr = NULL;
  66                         it->dataptr = ARR_DATA_PTR(a->xpn.fvalue);
  67                         it->bitmapptr = ARR_NULLBITMAP(a->xpn.fvalue);
  68                 }
  69         }
  70         else
  71         {
  72                 it->datumptr = NULL;
  73                 it->isnullptr = NULL;
  74                 it->dataptr = ARR_DATA_PTR((ArrayType *) a);
  75                 it->bitmapptr = ARR_NULLBITMAP((ArrayType *) a);
  76         }
  77         it->bitmask = 1;
  78 }
  79
  80 static inline Datum
  81 array_iter_next(array_iter *it, bool *isnull, int i,
  82                                 int elmlen, bool elmbyval, char elmalign)
  83 {
  84         Datum           ret;
  85
  86         if (it->datumptr)
  87         {
  88                 ret = it->datumptr[i];
  89                 *isnull = it->isnullptr ? it->isnullptr[i] : false;
  90         }
  91         else
  92         {
  93                 if (it->bitmapptr && (*(it->bitmapptr) & it->bitmask) == 0)
  94                 {
  95                         *isnull = true;
  96                         ret = (Datum) 0;
  97                 }
  98                 else
  99                 {
 100                         *isnull = false;
 101                         ret = fetch_att(it->dataptr, elmbyval, elmlen);
 102                         it->dataptr = att_addlength_pointer(it->dataptr, elmlen,
 103                                                                                                 it->dataptr);
 104                         it->dataptr = (char *) att_align_nominal(it->dataptr, elmalign);
 105                 }
 106                 it->bitmask <<= 1;
 107                 if (it->bitmask == 0x100)
 108                 {
 109                         if (it->bitmapptr)
 110                                 it->bitmapptr++;
 111                         it->bitmask = 1;
 112                 }
 113         }
 114
 115         return ret;
 116 }
 117
 118 #endif                                                  /* ARRAYACCESS_H */