SetOperations.h

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//===-- llvm/ADT/SetOperations.h - Generic Set Operations -------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file defines generic set operations that may be used on set's of
/// different types, and different element types.
///
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_ADT_SETOPERATIONS_H
#define LLVM_ADT_SETOPERATIONS_H
 
#include "llvm/ADT/STLExtras.h"
 
namespace llvm {
 
namespace detail {
template <typename Set, typename Fn>
using check_has_member_remove_if_t =
    decltype(std::declval<Set>().remove_if(std::declval<Fn>()));
 
template <typename Set, typename Fn>
static constexpr bool HasMemberRemoveIf =
    is_detected<check_has_member_remove_if_t, Set, Fn>::value;
} // namespace detail
 
/// set_union(A, B) - Compute A := A u B, return whether A changed.
///
template <class S1Ty, class S2Ty> bool set_union(S1Ty &S1, const S2Ty &S2) {
  bool Changed = false;
 
  for (typename S2Ty::const_iterator SI = S2.begin(), SE = S2.end(); SI != SE;
       ++SI)
    if (S1.insert(*SI).second)
      Changed = true;
 
  return Changed;
}
 
/// set_intersect(A, B) - Compute A := A ^ B
/// Identical to set_intersection, except that it works on set<>'s and
/// is nicer to use.  Functionally, this iterates through S1, removing
/// elements that are not contained in S2.
///
template <class S1Ty, class S2Ty> void set_intersect(S1Ty &S1, const S2Ty &S2) {
  auto Pred = [&S2](const auto &E) { return !S2.count(E); };
  if constexpr (detail::HasMemberRemoveIf<S1Ty, decltype(Pred)>) {
    S1.remove_if(Pred);
  } else {
    for (typename S1Ty::iterator I = S1.begin(); I != S1.end();) {
      const auto &E = *I;
      ++I;
      if (!S2.count(E))
        S1.erase(E); // Erase element if not in S2
    }
  }
}
 
template <class S1Ty, class S2Ty>
S1Ty set_intersection_impl(const S1Ty &S1, const S2Ty &S2) {
  S1Ty Result;
  for (typename S1Ty::const_iterator SI = S1.begin(), SE = S1.end(); SI != SE;
       ++SI)
    if (S2.count(*SI))
      Result.insert(*SI);
  return Result;
}
 
/// set_intersection(A, B) - Return A ^ B
template <class S1Ty, class S2Ty>
S1Ty set_intersection(const S1Ty &S1, const S2Ty &S2) {
  if (S1.size() < S2.size())
    return set_intersection_impl(S1, S2);
  else
    return set_intersection_impl(S2, S1);
}
 
/// set_difference(A, B) - Return A - B
///
template <class S1Ty, class S2Ty>
S1Ty set_difference(const S1Ty &S1, const S2Ty &S2) {
  S1Ty Result;
  for (typename S1Ty::const_iterator SI = S1.begin(), SE = S1.end(); SI != SE;
       ++SI)
    if (!S2.count(*SI)) // if the element is not in set2
      Result.insert(*SI);
  return Result;
}
 
/// set_subtract(A, B) - Compute A := A - B
///
template <class S1Ty, class S2Ty> void set_subtract(S1Ty &S1, const S2Ty &S2) {
  for (typename S2Ty::const_iterator SI = S2.begin(), SE = S2.end(); SI != SE;
       ++SI)
    S1.erase(*SI);
}
 
/// set_subtract(A, B, C, D) - Compute A := A - B, set C to the elements of B
/// removed from A (A ^ B), and D to the elements of B not found in and removed
/// from A (B - A).
template <class S1Ty, class S2Ty>
void set_subtract(S1Ty &S1, const S2Ty &S2, S1Ty &Removed, S1Ty &Remaining) {
  for (typename S2Ty::const_iterator SI = S2.begin(), SE = S2.end(); SI != SE;
       ++SI)
    if (S1.erase(*SI))
      Removed.insert(*SI);
    else
      Remaining.insert(*SI);
}
 
/// set_is_subset(A, B) - Return true iff A in B
///
template <class S1Ty, class S2Ty>
bool set_is_subset(const S1Ty &S1, const S2Ty &S2) {
  if (S1.size() > S2.size())
    return false;
  for (const auto It : S1)
    if (!S2.count(It))
      return false;
  return true;
}
 
} // namespace llvm
 
#endif