data_table.h

#pragma once

#include <stdbool.h>

/** A data table, with fast membership testing.
 *
 * Data tables are static arrays of data, with keys ranging from 0 to N-1. To
 * distinguish unset elements from 0 values, tables also contain an array
 * indicating whether a value has been set.
 *
 * The total size of a table is (N*sizeof(T))+N bytes. To avoid the overhead
 * of using two arrays, see optional.h, which trades value range for a
 * very compact representation of "optional" values.
 */
#define data_table(T, N)                        \
  struct { bool isset[N]; int data[N]; }

#define data_table_create(T, N)                     \
  ((data_table (T, N)) { 0, 0 })

/** Set table value for key.
 */
#define data_table_set(i, x, t)                  \
  ({                                             \
    let _i = i;                                  \
    let _x = x;                                  \
    (t)->data[_i] = _x;                          \
    (t)->isset[_i] = 1;                          \
  })

/** Unset table value for key.
 */
#define data_table_unset(i, t)                  \
  ({                                            \
    let _i = i;                                 \
    (t)->isset[_i] = 0;                         \
  })

/** Test whether key has value. */
#define data_table_isset(i, t)                  \
  ({ let _i = i; (t)->isset[_i]; })

/** Retrieve key value. */
#define data_table_get(i, t)                    \
  ({ let _i = i; (t)->data[_i]; })

/** Define a static table. */
#define deftable(NAME, T, N)                          \
  static let tbl_ ## NAME = data_table_create (T, N)

/** Refer to a static table. */
#define t(NAME) &(tbl_ ## NAME)