From 27c341db41bc9df5c6f19cde65f002d6f1c2eb3c Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <peter@pcc.me.uk>
Date: Fri, 26 Jan 2018 21:23:27 +0000
Subject: [PATCH] Fix the BinaryPredicate form of std::is_permutation to not
 rely on operator==

According to [1], forms 2 and 4 of std::is_permutation should use the passed in
binary predicate to compare elements. operator== should only be used for forms
1 and 3 which do not take a binary predicate.

This CL fixes forms 2 and 4 which relied on operator== for some comparisons.

[1] http://en.cppreference.com/w/cpp/algorithm/is_permutation

Patch by Thomas Anderson!

Differential Revision: https://reviews.llvm.org/D42518

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@323563 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/algorithm                             | 12 ++++++++--
 .../is_permutation_pred.pass.cpp              | 24 +++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/include/algorithm b/include/algorithm
index 3493428f9..9d2690d5b 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -1418,7 +1418,11 @@ is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
     for (_ForwardIterator1 __i = __first1; __i != __last1; ++__i)
     {
     //  Have we already counted the number of *__i in [f1, l1)?
-        if (find(__first1, __i, *__i) == __i) {
+        _ForwardIterator1 __match = __first1;
+        for (; __match != __i; ++__match)
+            if (__pred(*__match, *__i))
+                break;
+        if (__match == __i) {
             // Count number of *__i in [f2, l2)
             _D1 __c2 = 0;
             for (_ForwardIterator2 __j = __first2; __j != __last2; ++__j)
@@ -1479,7 +1483,11 @@ __is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
     for (_ForwardIterator1 __i = __first1; __i != __last1; ++__i)
     {
     //  Have we already counted the number of *__i in [f1, l1)?
-        if (find(__first1, __i, *__i) == __i) {
+        _ForwardIterator1 __match = __first1;
+        for (; __match != __i; ++__match)
+            if (__pred(*__match, *__i))
+                break;
+        if (__match == __i) {
             // Count number of *__i in [f2, l2)
             _D1 __c2 = 0;
             for (_ForwardIterator2 __j = __first2; __j != __last2; ++__j)
diff --git a/test/std/algorithms/alg.nonmodifying/alg.is_permutation/is_permutation_pred.pass.cpp b/test/std/algorithms/alg.nonmodifying/alg.is_permutation/is_permutation_pred.pass.cpp
index 6c40ce368..12bd938d2 100644
--- a/test/std/algorithms/alg.nonmodifying/alg.is_permutation/is_permutation_pred.pass.cpp
+++ b/test/std/algorithms/alg.nonmodifying/alg.is_permutation/is_permutation_pred.pass.cpp
@@ -736,6 +736,30 @@ int main()
                                    forward_iterator<const int*>(ib),
                                    forward_iterator<const int*>(ib + sa),
                                    std::equal_to<const int>()) == false);
+#endif
+    }
+    {
+      struct S {
+          S(int i) : i_(i) {}
+          bool operator==(const S& other) = delete;
+          int i_;
+      };
+      struct eq {
+          bool operator()(const S& a, const S&b) { return a.i_ == b.i_; }
+      };
+      const S a[] = {S(0), S(1)};
+      const S b[] = {S(1), S(0)};
+      const unsigned sa = sizeof(a)/sizeof(a[0]);
+      assert(std::is_permutation(forward_iterator<const S*>(a),
+                                 forward_iterator<const S*>(a + sa),
+                                 forward_iterator<const S*>(b),
+                                 eq()));
+#if TEST_STD_VER >= 14
+      assert(std::is_permutation(forward_iterator<const S*>(a),
+                                 forward_iterator<const S*>(a + sa),
+                                 forward_iterator<const S*>(b),
+                                 forward_iterator<const S*>(b + sa),
+                                 eq()));
 #endif
     }