/* Plural expression evaluation.

   Copyright (C) 2000-2023 Free Software Foundation, Inc.

   This program 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 2.1 of the License, or

   (at your option) any later version.

   This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.  */

#ifndef STATIC

#define STATIC static

#endif

/* While the bison parser is able to support expressions of a maximum depth

   of YYMAXDEPTH = 10000, the runtime evaluation of a parsed plural expression

   has a smaller maximum recursion depth.

   If we did not limit the recursion depth, a program that just invokes

   ngettext() on a thread other than the main thread could get a crash by

   stack overflow in the following circumstances:

     - On systems with glibc, after the stack size has been reduced,

       e.g. on x86_64 systems after "ulimit -s 260".

       This stack size is only sufficient for ca. 3919 recursions.

       Cf. <https://unix.stackexchange.com/questions/620720/>

     - On systems with musl libc, because there the thread stack size (for a

       thread other than the main thread) by default is only 128 KB, see

       <https://wiki.musl-libc.org/functional-differences-from-glibc.html#Thread-stack-size>.

     - On AIX 7 systems, because there the thread stack size (for a thread

       other than the main thread) by default is only 96 KB, see

       <https://www.ibm.com/docs/en/aix/7.1?topic=programming-threads-library-options>.

       This stack size is only sufficient for between 887 and 1363 recursions,

       depending on the compiler and compiler optimization options.

   A maximum depth of 100 is a large enough for all practical needs

   and also small enough to avoid stack overflow even with small thread stack

   sizes.  */

#ifndef EVAL_MAXDEPTH

# define EVAL_MAXDEPTH 100

#endif

/* A shorthand that denotes a successful evaluation result with a value V.  */

#define OK(v) (struct eval_result) { .status = PE_OK, .value = (v) }

/* Evaluates a plural expression PEXP for n=N, up to ALLOWED_DEPTH.  */

static struct eval_result

plural_eval_recurse (const struct expression *pexp, unsigned long int n,

         unsigned int allowed_depth)

{

  if (allowed_depth == 0)

    /* The allowed recursion depth is exhausted.  */

    return (struct eval_result) { .status = PE_STACKOVF };

  allowed_depth--;

  switch (pexp->nargs)

    {

    case 0:

      switch (pexp->operation)

  {

  case var:

    return OK (n);

  case num:

    return OK (pexp->val.num);

  default:

    break;

  }

      /* NOTREACHED */

      break;

    case 1:

      {

  /* pexp->operation must be lnot.  */

  struct eval_result arg =

    plural_eval_recurse (pexp->val.args[0], n, allowed_depth);

  if (arg.status != PE_OK)

    return arg;

  return OK (! arg.value);

      }

    case 2:

      {

  struct eval_result leftarg =

    plural_eval_recurse (pexp->val.args[0], n, allowed_depth);

  if (leftarg.status != PE_OK)

    return leftarg;

  if (pexp->operation == lor)

    {

      if (leftarg.value)

        return OK (1);

      struct eval_result rightarg =

        plural_eval_recurse (pexp->val.args[1], n, allowed_depth);

      if (rightarg.status != PE_OK)

        return rightarg;

      return OK (rightarg.value ? 1 : 0);

    }

  else if (pexp->operation == land)

    {

      if (!leftarg.value)

        return OK (0);

      struct eval_result rightarg =

        plural_eval_recurse (pexp->val.args[1], n, allowed_depth);

      if (rightarg.status != PE_OK)

        return rightarg;

      return OK (rightarg.value ? 1 : 0);

    }

  else

    {

      struct eval_result rightarg =

        plural_eval_recurse (pexp->val.args[1], n, allowed_depth);

      if (rightarg.status != PE_OK)

        return rightarg;

      switch (pexp->operation)

        {

        case mult:

    return OK (leftarg.value * rightarg.value);

        case divide:

    if (rightarg.value == 0)

      return (struct eval_result) { .status = PE_INTDIV };

    return OK (leftarg.value / rightarg.value);

        case module:

    if (rightarg.value == 0)

      return (struct eval_result) { .status = PE_INTDIV };

    return OK (leftarg.value % rightarg.value);

        case plus:

    return OK (leftarg.value + rightarg.value);

        case minus:

    return OK (leftarg.value - rightarg.value);

        case less_than:

    return OK (leftarg.value < rightarg.value);

        case greater_than:

    return OK (leftarg.value > rightarg.value);

        case less_or_equal:

    return OK (leftarg.value <= rightarg.value);

        case greater_or_equal:

    return OK (leftarg.value >= rightarg.value);

        case equal:

    return OK (leftarg.value == rightarg.value);

        case not_equal:

    return OK (leftarg.value != rightarg.value);

        default:

    break;

        }

    }

  /* NOTREACHED */

  break;

      }

    case 3:

      {

  /* pexp->operation must be qmop.  */

  struct eval_result boolarg =

    plural_eval_recurse (pexp->val.args[0], n, allowed_depth);

  if (boolarg.status != PE_OK)

    return boolarg;

  return plural_eval_recurse (pexp->val.args[boolarg.value ? 1 : 2], n,

            allowed_depth);

      }

    }

  /* NOTREACHED */

  return (struct eval_result) { .status = PE_ASSERT };

}

/* Evaluates a plural expression PEXP for n=N.  */

STATIC

struct eval_result

plural_eval (const struct expression *pexp, unsigned long int n)

{

  return plural_eval_recurse (pexp, n, EVAL_MAXDEPTH);

}

#undef OK