tv.c

/*
 * Project:     libFIRM
 * File name:   ir/tv/tv.c
 * Purpose:     Representation of and static computations on target machine
 *              values.
 * Author:      Mathias Heil
 * Modified by:
 * Created:
 * CVS-ID:      $Id$
 * Copyright:   (c) 2003 Universitt Karlsruhe
 * Licence:     This file protected by GPL -  GNU GENERAL PUBLIC LICENSE.
 */

/*
 *    Values are stored in a format depending upon chosen arithmetic
 *    module. Default uses strcalc and fltcalc.
 *
 */

/* This implementation assumes:
 *  - target has IEEE-754 floating-point arithmetic.  */


#ifdef HAVE_CONFIG_H
# include "config.h"
#endif


#include <assert.h>         /* assertions */
#include <stdlib.h>         /* atoi() */
#ifdef HAVE_STRING_H
# include <string.h>         /* nice things for strings */
#endif
#ifdef HAVE_STRINGS_H
#include <strings.h>        /* strings.h also includes bsd only function strcasecmp */
#endif
#ifdef HAVE_STDLIB_H
# include <stdlib.h>
#endif
#ifdef HAVE_ALLOCA_H
# include <alloca.h>
#endif
#ifdef HAVE_MALLOC_H
# include <malloc.h>
#endif

#include "tv_t.h"
#include "set.h"            /* to store tarvals in */
#include "entity_t.h"       /* needed to store pointers to entities */
#include "irmode_t.h"
#include "irnode.h"         /* defines boolean return values (pnc_number)*/
#include "strcalc.h"
#include "fltcalc.h"
#include "irtools.h"
#include "xmalloc.h"
#include "firm_common.h"

/** Size of hash tables.  Should correspond to average number of distinct constant
    target values */
#define N_CONSTANTS 2048

/* get the integer overflow mode */
#define GET_OVERFLOW_MODE() int_overflow_mode

/* unused, float to int doesn't work yet */
enum float_to_int_mode {
  TRUNCATE,
  ROUND
};

#define GET_FLOAT_TO_INT_MODE() TRUNCATE

#define SWITCH_NOINFINITY 0
#define SWITCH_NODENORMALS 0

/****************************************************************************
 *   local definitions and macros
 ****************************************************************************/
#ifndef NDEBUG
#  define TARVAL_VERIFY(a) tarval_verify((a))
#else
#  define TARVAL_VERIFY(a) ((void)0)
#endif

#define INSERT_TARVAL(tv) ((tarval*)set_insert(tarvals, (tv), sizeof(tarval), hash_tv((tv))))
#define FIND_TARVAL(tv) ((tarval*)set_find(tarvals, (tv), sizeof(tarval), hash_tv((tv))))

#define INSERT_VALUE(val, size) (set_insert(values, (val), size, hash_val((val), size)))
#define FIND_VALUE(val, size) (set_find(values, (val), size, hash_val((val), size)))

#define fail_verify(a) _fail_verify((a), __FILE__, __LINE__)
#if 0
static long long count = 0;
#  define ANNOUNCE() printf(__FILE__": call no. %lld (%s)\n", count++, __FUNCTION__);
#else
#  define ANNOUNCE() ((void)0)
#endif
/****************************************************************************
 *   private variables
 ****************************************************************************/
static struct set *tarvals;   /* container for tarval structs */
static struct set *values;    /* container for values */
static tarval_int_overflow_mode_t int_overflow_mode = TV_OVERFLOW_WRAP;

/****************************************************************************
 *   private functions
 ****************************************************************************/
#ifndef NDEBUG
static int hash_val(const void *value, unsigned int length);
static int hash_tv(tarval *tv);
static void _fail_verify(tarval *tv, const char* file, int line)
{
  /* print a memory image of the tarval and throw an assertion */
  if (tv)
    printf("%s:%d: Invalid tarval:\n  mode: %s\n value: [%p]\n", file, line, get_mode_name(tv->mode), tv->value);
  else
    printf("%s:%d: Invalid tarval (null)", file, line);
  assert(0);
}
#ifdef __GNUC__
INLINE static void tarval_verify(tarval *tv) __attribute__ ((unused));
#endif

INLINE static void tarval_verify(tarval *tv)
{
  assert(tv);
  assert(tv->mode);
  assert(tv->value);

  if ((tv == tarval_bad) || (tv == tarval_undefined)) return;
  if ((tv == tarval_b_true) || (tv == tarval_b_false)) return;

  if (!FIND_TARVAL(tv)) fail_verify(tv);
  if (tv->length > 0 && !FIND_VALUE(tv->value, tv->length)) fail_verify(tv);

  return;
}
#endif /* NDEBUG */

/** Hash a tarval. */
static int hash_tv(tarval *tv) {
  return (PTR_TO_INT(tv->value) ^ PTR_TO_INT(tv->mode)) + tv->length;
}

/** Hash a value. Treat it as a byte array. */
static int hash_val(const void *value, unsigned int length) {
  unsigned int i;
  unsigned int hash = 0;

  /* scramble the byte - array */
  for (i = 0; i < length; i++)
  {
    hash += (hash << 5) ^ (hash >> 27) ^ ((char*)value)[i];
    hash += (hash << 11) ^ (hash >> 17);
  }

  return hash;
}

/** finds tarval with value/mode or creates new tarval */
static tarval *get_tarval(const void *value, int length, ir_mode *mode)
{
  tarval tv;

  tv.kind   = k_tarval;
  tv.mode   = mode;
  tv.length = length;
  if (length > 0) {
    /* if there already is such a value, it is returned, else value
     * is copied into the set */
    tv.value = INSERT_VALUE(value, length);
  } else {
    tv.value = value;
  }
  /* if there is such a tarval, it is returned, else tv is copied
   * into the set */
  return (tarval *)INSERT_TARVAL(&tv);
}

/**
 * handle overflow
 */
static tarval *get_tarval_overflow(const void *value, int length, ir_mode *mode)
{
  switch (get_mode_sort(mode))
  {
    case irms_int_number:
      if (sc_comp(value, get_mode_max(mode)->value) == 1) {
        switch (GET_OVERFLOW_MODE()) {
          case TV_OVERFLOW_SATURATE:
            return get_mode_max(mode);
          case TV_OVERFLOW_WRAP:
            {
              char *temp = alloca(sc_get_buffer_length());
              sc_val_from_ulong(-1, temp);
              sc_and(temp, value, temp);
			  /* the sc_ module expects that all bits are set ... */
              sign_extend(temp, mode);
              return get_tarval(temp, length, mode);
            }
          case TV_OVERFLOW_BAD:
            return tarval_bad;
          default:
            return get_tarval(value, length, mode);
        }
      }
      if (sc_comp(value, get_mode_min(mode)->value) == -1) {
        switch (GET_OVERFLOW_MODE()) {
          case TV_OVERFLOW_SATURATE:
            return get_mode_min(mode);
          case TV_OVERFLOW_WRAP:
            {
              char *temp = alloca(sc_get_buffer_length());
              sc_val_from_ulong(-1, temp);
              sc_and(temp, value, temp);
              return get_tarval(temp, length, mode);
            }
          case TV_OVERFLOW_BAD:
            return tarval_bad;
          default:
            return get_tarval(value, length, mode);
        }
      }
      break;

    case irms_float_number:
      if (SWITCH_NOINFINITY && fc_is_inf(value))
      {
        return fc_is_negative(value)?get_mode_min(mode):get_mode_max(mode);
      }

      if (SWITCH_NODENORMALS && fc_is_subnormal(value))
      {
        return get_mode_null(mode);
      }
      break;

    default:
      break;
  }
  return get_tarval(value, length, mode);
}

/*
 *   public variables declared in tv.h
 */
static tarval reserved_tv[4];

tarval *tarval_bad       = &reserved_tv[0];
tarval *tarval_undefined = &reserved_tv[1];
tarval *tarval_b_false   = &reserved_tv[2];
tarval *tarval_b_true    = &reserved_tv[3];

/*
 *   public functions declared in tv.h
 */

/*
 * Constructors =============================================================
 */
tarval *new_tarval_from_str(const char *str, size_t len, ir_mode *mode)
{
  ANNOUNCE();
  assert(str);
  assert(len);
  assert(mode);

  switch (get_mode_sort(mode))
  {
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
      assert(0);
      break;

    case irms_internal_boolean:
      /* match [tT][rR][uU][eE]|[fF][aA][lL][sS][eE] */
      if (strcasecmp(str, "true")) return tarval_b_true;
      else if (strcasecmp(str, "false")) return tarval_b_true;
      else
        /* XXX This is C semantics */
    return atoi(str) ? tarval_b_true : tarval_b_false;

    case irms_float_number:
      switch(get_mode_size_bits(mode)) {
        case 32:
          fc_val_from_str(str, len, 8, 23, NULL);
          break;
        case 64:
          fc_val_from_str(str, len, 11, 52, NULL);
          break;
        case 80:
          fc_val_from_str(str, len, 15, 64, NULL);
          break;
      }
      return get_tarval(fc_get_buffer(), fc_get_buffer_length(), mode);

    case irms_reference:
      /* same as integer modes */
    case irms_int_number:
    case irms_character:
      sc_val_from_str(str, len, NULL, mode);
      return get_tarval(sc_get_buffer(), sc_get_buffer_length(), mode);
  }

  assert(0);  /* can't be reached, can it? */
  return NULL;
}

/*
 * helper function, create a tarval from long
 */
tarval *new_tarval_from_long(long l, ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  switch(get_mode_sort(mode))
  {
    case irms_internal_boolean:
      /* XXX C semantics ! */
      return l ? tarval_b_true : tarval_b_false ;

    case irms_reference:
      /* same as integer modes */
    case irms_int_number:
    case irms_character:
      sc_val_from_long(l, NULL);
      return get_tarval(sc_get_buffer(), sc_get_buffer_length(), mode);

    case irms_float_number:
      return new_tarval_from_double((long double)l, mode);

    default:
      assert(0 && "unsupported mode sort");
  }
  return NULL;
}

/* returns non-zero if can be converted to long */
int tarval_is_long(tarval *tv)
{
  mode_sort sort = get_mode_sort(tv->mode);

  ANNOUNCE();
  if (sort != irms_int_number && sort != irms_character) return 0;

  if (get_mode_size_bits(tv->mode) > sizeof(long)<<3)
  {
    /* the value might be too big to fit in a long */
    sc_max_from_bits(sizeof(long)<<3, 0, NULL);
    if (sc_comp(sc_get_buffer(), tv->value) == -1)
    {
      /* really doesn't fit */
      return 0;
    }
  }
  return 1;
}

/* this might overflow the machine's long, so use only with small values */
long get_tarval_long(tarval* tv)
{
  ANNOUNCE();
  assert(tarval_is_long(tv) && "tarval too big to fit in long");

  return sc_val_to_long(tv->value);
}

tarval *new_tarval_from_double(long double d, ir_mode *mode)
{
  ANNOUNCE();
  assert(mode && (get_mode_sort(mode) == irms_float_number));

  switch (get_mode_size_bits(mode)) {
    case 32:
      fc_val_from_float(d, 8, 23, NULL);
      break;
    case 64:
      fc_val_from_float(d, 11, 52, NULL);
      break;
    case 80:
      fc_val_from_float(d, 15, 64, NULL);
      break;
  }
  return get_tarval(fc_get_buffer(), fc_get_buffer_length(), mode);
}

/* returns non-zero if can be converted to double */
int tarval_is_double(tarval *tv)
{
  ANNOUNCE();
  assert(tv);

  return (get_mode_sort(tv->mode) == irms_float_number);
}

long double get_tarval_double(tarval *tv)
{
  ANNOUNCE();
  assert(tarval_is_double(tv));

  return fc_val_to_float(tv->value);
}


/*
 * Access routines for tarval fields ========================================
 */

/* get the mode of the tarval */
ir_mode *(get_tarval_mode)(const tarval *tv) {
  return _get_tarval_mode(tv);
}

/*
 * Special value query functions ============================================
 *
 * These functions calculate and return a tarval representing the requested
 * value.
 * The functions get_mode_{Max,Min,...} return tarvals retrieved from these
 * functions, but these are stored on initialization of the irmode module and
 * therefore the irmode functions should be prefered to the functions below.
 */

tarval *(get_tarval_bad)(void) {
  return _get_tarval_bad();
}

tarval *(get_tarval_undefined)(void) {
  return _get_tarval_undefined();
}

tarval *(get_tarval_b_false)(void) {
  return _get_tarval_b_false();
}

tarval *(get_tarval_b_true)(void) {
  return _get_tarval_b_true();
}

tarval *get_tarval_max(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  switch(get_mode_sort(mode))
  {
    case irms_reference:
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
      assert(0);
      break;

    case irms_internal_boolean:
      return tarval_b_true;

    case irms_float_number:
      switch(get_mode_size_bits(mode))
      {
        case 32:
          fc_get_max(8, 23, NULL);
          break;
        case 64:
          fc_get_max(11, 52, NULL);
          break;
        case 80:
          fc_get_max(15, 64, NULL);
          break;
      }
      return get_tarval(fc_get_buffer(), fc_get_buffer_length(), mode);

    case irms_int_number:
    case irms_character:
      sc_max_from_bits(get_mode_size_bits(mode), mode_is_signed(mode), NULL);
      return get_tarval(sc_get_buffer(), sc_get_buffer_length(), mode);
  }
  return tarval_bad;
}

tarval *get_tarval_min(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  switch(get_mode_sort(mode))
  {
    case irms_reference:
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
      assert(0);
      break;

    case irms_internal_boolean:
      return tarval_b_false;

    case irms_float_number:
      switch(get_mode_size_bits(mode))
      {
        case 32:
          fc_get_min(8, 23, NULL);
          break;
        case 64:
          fc_get_min(11, 52, NULL);
          break;
        case 80:
          fc_get_min(15, 64, NULL);
          break;
      }
      return get_tarval(fc_get_buffer(), fc_get_buffer_length(), mode);

    case irms_int_number:
    case irms_character:
      sc_min_from_bits(get_mode_size_bits(mode), mode_is_signed(mode), NULL);
      return get_tarval(sc_get_buffer(), sc_get_buffer_length(), mode);
  }
  return tarval_bad;
}

static long _null_value;

tarval *get_tarval_null(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  switch(get_mode_sort(mode))
  {
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
    case irms_internal_boolean:
      assert(0);
      break;

    case irms_float_number:
      return new_tarval_from_double(0.0, mode);

    case irms_int_number:
    case irms_character:
      return new_tarval_from_long(0l,  mode);

    case irms_reference:
      return new_tarval_from_long(_null_value, mode);
  }
  return tarval_bad;
}

tarval *get_tarval_one(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  switch(get_mode_sort(mode))
  {
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
    case irms_internal_boolean:
    case irms_reference:
      assert(0);
      break;

    case irms_float_number:
      return new_tarval_from_double(1.0, mode);

    case irms_int_number:
    case irms_character:
      return new_tarval_from_long(1l, mode);
      break;
  }
  return tarval_bad;
}

tarval *get_tarval_minus_one(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  switch(get_mode_sort(mode))
  {
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
    case irms_internal_boolean:
    case irms_reference:
      assert(0);
      break;

    case irms_float_number:
      return mode_is_signed(mode) ? new_tarval_from_double(-1.0, mode) : tarval_bad;

    case irms_int_number:
    case irms_character:
      return mode_is_signed(mode) ? new_tarval_from_long(-1l, mode) : tarval_bad;
  }
  return tarval_bad;
}

tarval *get_tarval_nan(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  if (get_mode_sort(mode) == irms_float_number) {
    switch(get_mode_size_bits(mode))
    {
      case 32:
        fc_get_qnan(8, 23, NULL);
        break;
      case 64:
        fc_get_qnan(11, 52, NULL);
        break;
      case 80:
        fc_get_qnan(15, 64, NULL);
        break;
    }
    return get_tarval(fc_get_buffer(), fc_get_buffer_length(), mode);
  }
  else {
    assert(0 && "tarval is not floating point");
    return tarval_bad;
  }
}

tarval *get_tarval_plus_inf(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  if (get_mode_sort(mode) == irms_float_number) {
    switch(get_mode_size_bits(mode))
    {
      case 32:
        fc_get_plusinf(8, 23, NULL);
        break;
      case 64:
        fc_get_plusinf(11, 52, NULL);
        break;
      case 80:
        fc_get_plusinf(15, 64, NULL);
        break;
    }
    return get_tarval(fc_get_buffer(), fc_get_buffer_length(), mode);
  }
  else {
    assert(0 && "tarval is not floating point");
    return tarval_bad;
  }
}

tarval *get_tarval_minus_inf(ir_mode *mode)
{
  ANNOUNCE();
  assert(mode);

  if (get_mode_n_vector_elems(mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  if (get_mode_sort(mode) == irms_float_number) {
    switch(get_mode_size_bits(mode))
    {
    case 32:
      fc_get_minusinf(8, 23, NULL);
      break;
    case 64:
      fc_get_minusinf(11, 52, NULL);
      break;
    case 80:
      fc_get_minusinf(15, 64, NULL);
      break;
    }
    return get_tarval(fc_get_buffer(), fc_get_buffer_length(), mode);
  }
  else {
    assert(0 && "tarval is not floating point");
    return tarval_bad;
  }
}

/*
 * Arithmethic operations on tarvals ========================================
 */

/*
 * test if negative number, 1 means 'yes'
 */
int tarval_is_negative(tarval *a)
{
  ANNOUNCE();
  assert(a);

  if (get_mode_n_vector_elems(a->mode) > 1) {
    /* vector arithmetic not implemented yet */
    assert(0 && "tarval_is_negative is not allowed for vector modes");
    return 0;
  }

  switch (get_mode_sort(a->mode))
  {
    case irms_int_number:
      if (!mode_is_signed(a->mode)) return 0;
      else
    return sc_comp(a->value, get_mode_null(a->mode)->value) == -1 ? 1 : 0;

    case irms_float_number:
      return fc_comp(a->value, get_mode_null(a->mode)->value) == -1 ? 1 : 0;

    default:
      assert(0 && "not implemented");
      return 0;
  }
}

/*
 * test if null, 1 means 'yes'
 */
int tarval_is_null(tarval *a)
{
  ir_mode *m = get_tarval_mode(a);

  return a == get_tarval_null(m);
}

/*
 * test if one, 1 means 'yes'
 */
int tarval_is_one(tarval *a)
{
  ir_mode *m = get_tarval_mode(a);

  return a == get_tarval_one(m);
}

/*
 * comparison
 */
pn_Cmp tarval_cmp(tarval *a, tarval *b)
{
  ANNOUNCE();
  assert(a);
  assert(b);

  if (a == tarval_bad || b == tarval_bad) {
    assert(0 && "Comparison with tarval_bad");
    return pn_Cmp_False;
  }

  if (a == tarval_undefined || b == tarval_undefined)
    return pn_Cmp_False;

  if (a->mode != b->mode)
    return pn_Cmp_False;

  if (get_mode_n_vector_elems(a->mode) > 1) {
    /* vector arithmetic not implemented yet */
    assert(0 && "cmp not implemented for vector modes");
  }

  /* Here the two tarvals are unequal and of the same mode */
  switch (get_mode_sort(a->mode))
  {
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
    case irms_reference:
      if (a == b)
        return pn_Cmp_Eq;
      return pn_Cmp_False;

    case irms_float_number:
      /*
       * BEWARE: we cannot compare a == b here, because
       * a NaN is always Unordered to any other value, even to itself!
       */
      switch (fc_comp(a->value, b->value)) {
        case -1: return pn_Cmp_Lt;
        case  0: return pn_Cmp_Eq;
        case  1: return pn_Cmp_Gt;
        case  2: return pn_Cmp_Uo;
        default: return pn_Cmp_False;
      }
    case irms_int_number:
    case irms_character:
      if (a == b)
        return pn_Cmp_Eq;
      return sc_comp(a->value, b->value) == 1 ? pn_Cmp_Gt : pn_Cmp_Lt;

    case irms_internal_boolean:
      if (a == b)
        return pn_Cmp_Eq;
      return a == tarval_b_true ? pn_Cmp_Gt : pn_Cmp_Lt;
  }
  return pn_Cmp_False;
}

/*
 * convert to other mode
 */
tarval *tarval_convert_to(tarval *src, ir_mode *m)
{
  char *buffer;

  ANNOUNCE();
  assert(src);
  assert(m);

  if (src->mode == m) return src;

  if (get_mode_n_vector_elems(src->mode) > 1) {
    /* vector arithmetic not implemented yet */
    return tarval_bad;
  }

  switch (get_mode_sort(src->mode))
  {
    case irms_control_flow:
    case irms_memory:
    case irms_auxiliary:
      break;

    /* cast float to something */
    case irms_float_number:
      switch (get_mode_sort(m)) {
        case irms_float_number:
          switch (get_mode_size_bits(m))
          {
            case 32:
              fc_cast(src->value, 8, 23, NULL);
              break;
            case 64:
              fc_cast(src->value, 11, 52, NULL);
              break;
            case 80:
              fc_cast(src->value, 15, 64, NULL);
              break;
            default:
              break;
          }
          return get_tarval(fc_get_buffer(), fc_get_buffer_length(), m);

        case irms_int_number:
          switch (GET_FLOAT_TO_INT_MODE())
          {
            case TRUNCATE:
              fc_int(src->value, NULL);
              break;
            case ROUND:
              fc_rnd(src->value, NULL);
              break;
            default:
              assert(0);
              break;
          }
          /* FIXME: floating point unit can't produce a value in integer
           * representation
           * an intermediate representation is needed here first. */
          /*  return get_tarval(); */
          return tarval_bad;

        default:
          /* the rest can't be converted */
          return tarval_bad;
      }
      break;

    /* cast int to something */
    case irms_int_number:
      switch (get_mode_sort(m)) {
        case irms_int_number:
        case irms_character:
          return get_tarval_overflow(src->value, src->length, m);

        case irms_internal_boolean:
          /* XXX C semantics */
          if (src == get_mode_null(src->mode)) return tarval_b_false;
          else return tarval_b_true;

        case irms_float_number:
          /* XXX floating point unit does not understand internal integer
           * representation, convert to string first, then create float from
           * string */
          buffer = alloca(100);
          /* decimal string representation because hexadecimal output is
           * interpreted unsigned by fc_val_from_str, so this is a HACK */
          snprintf(buffer, 100, "%s",
                   sc_print(src->value, get_mode_size_bits(src->mode), SC_DEC));
          buffer[100 - 1] = '\0';
          switch (get_mode_size_bits(m))
          {
            case 32:
              fc_val_from_str(buffer, 0, 8, 23, NULL);
              break;
            case 64:
              fc_val_from_str(buffer, 0, 11, 52, NULL);
              break;
            case 80:
              fc_val_from_str(buffer, 0, 15, 64, NULL);
              break;
          }
          return get_tarval(fc_get_buffer(), fc_get_buffer_length(), m);

        case irms_reference:
          /* allow 0 to be casted */
          if (src == get_mode_null(src->mode))
            return get_mode_null(m);
          break;

        default:
          break;
      }
      break;

    case irms_internal_boolean:
      switch (get_mode_sort(m))
      {
        case irms_int_number:
          if (src == tarval_b_true) return get_mode_one(m);
          else return get_mode_null(m);

        default:
          break;
      }
      break;

    case irms_character:
      break;
    case irms_reference:
      break;
  }

  return tarval_bad;
}

/*
 * bitwise negation
 */
tarval *tarval_not(tarval *a)
{
  char *buffer;

  ANNOUNCE();
  assert(a);

  /* works for vector mode without changes */

  switch (get_mode_sort(a->mode))
  {
    case irms_int_number:
      buffer = alloca(sc_get_buffer_length());
      sc_not(a->value, buffer);
      return get_tarval(buffer, a->length, a->mode);

    case irms_internal_boolean:
      if (a == tarval_b_true)
        return tarval_b_false;
      if (a == tarval_b_false)
        return tarval_b_true;
      return tarval_bad;

    default: