rand-fst.h

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// Copyright 2005-2024 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the 'License');
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an 'AS IS' BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#ifndef FST_TEST_RAND_FST_H_
#define FST_TEST_RAND_FST_H_

#include <cstddef>
#include <cstdint>
#include <random>

#include <fst/log.h>
#include <fst/mutable-fst.h>
#include <fst/properties.h>
#include <fst/verify.h>

namespace fst {

// Generates a random FST.
template <class Arc, class Generate>
void RandFst(const int num_random_states, const int num_random_arcs,
             const int num_random_labels, const float acyclic_prob,
             Generate generate, uint64_t seed, MutableFst<Arc> *fst) {
  using Label = typename Arc::Label;
  using StateId = typename Arc::StateId;
  using Weight = typename Arc::Weight;

  // Determines direction of the arcs wrt state numbering. This way we
  // can force acyclicity when desired.
  enum ArcDirection {
    ANY_DIRECTION = 0,
    FORWARD_DIRECTION = 1,
    REVERSE_DIRECTION = 2,
    NUM_DIRECTIONS = 3
  };

  std::mt19937_64 rand(seed);
  const StateId ns =
      std::uniform_int_distribution<>(0, num_random_states - 1)(rand);
  std::uniform_int_distribution<size_t> arc_dist(0, num_random_arcs - 1);
  std::uniform_int_distribution<Label> label_dist(0, num_random_labels - 1);
  std::uniform_int_distribution<StateId> ns_dist(0, ns - 1);

  ArcDirection arc_direction = ANY_DIRECTION;
  if (!std::bernoulli_distribution(acyclic_prob)(rand)) {
    arc_direction = std::bernoulli_distribution(.5)(rand) ? FORWARD_DIRECTION
                                                          : REVERSE_DIRECTION;
  }

  fst->DeleteStates();

  if (ns == 0) return;
  fst->AddStates(ns);

  const StateId start = ns_dist(rand);
  fst->SetStart(start);

  const size_t na = arc_dist(rand);
  for (size_t n = 0; n < na; ++n) {
    StateId s = ns_dist(rand);
    Arc arc;
    arc.ilabel = label_dist(rand);
    arc.olabel = label_dist(rand);
    arc.weight = generate();
    arc.nextstate = ns_dist(rand);
    if ((arc_direction == FORWARD_DIRECTION ||
         arc_direction == REVERSE_DIRECTION) &&
        s == arc.nextstate) {
      continue;  // Skips self-loops.
    }

    if ((arc_direction == FORWARD_DIRECTION && s > arc.nextstate) ||
        (arc_direction == REVERSE_DIRECTION && s < arc.nextstate)) {
      StateId t = s;  // reverses arcs
      s = arc.nextstate;
      arc.nextstate = t;
    }

    fst->AddArc(s, arc);
  }

  const StateId nf = std::uniform_int_distribution<>(0, ns)(rand);
  for (StateId n = 0; n < nf; ++n) {
    const StateId s = ns_dist(rand);
    fst->SetFinal(s, generate());
  }
  VLOG(1) << "Check FST for sanity (including property bits).";
  CHECK(Verify(*fst));

  // Get/compute all properties.
  const uint64_t props = fst->Properties(kFstProperties, true);

  // Select random set of properties to be unknown.
  uint64_t mask = 0;
  for (int n = 0; n < 8; ++n) {
    mask |= std::uniform_int_distribution<>(0, 0xff)(rand);
    mask <<= 8;
  }
  mask &= ~kTrinaryProperties;
  fst->SetProperties(props & ~mask, mask);
}

}  // namespace fst

#endif  // FST_TEST_RAND_FST_H_