[libc++][C++03] partially cherry-pick #122641

[philnik777]

This patch only cherry-picks the parts that actually fix the issue, but not the numerous NFC refactorings around it.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

This patch only cherry-picks the parts that actually fix the issue, but not the numerous NFC refactorings around it.

---

Full diff: https://github.com/llvm/llvm-project/pull/157596.diff

2 Files Affected:

• (modified) libcxx/include/__cxx03/__algorithm/find.h (+3-3)
• (modified) libcxx/test/std/algorithms/alg.nonmodifying/alg.find/find.pass.cpp (-1)

diff --git a/libcxx/include/__cxx03/__algorithm/find.h b/libcxx/include/__cxx03/__algorithm/find.h
index ddf8201c6e951..baa8e4ccd052f 100644
--- a/libcxx/include/__cxx03/__algorithm/find.h
+++ b/libcxx/include/__cxx03/__algorithm/find.h
@@ -105,7 +105,7 @@ __find_bool(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
     __storage_type __m     = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
     __storage_type __b     = std::__invert_if<!_ToFind>(*__first.__seg_) & __m;
     if (__b)
-      return _It(__first.__seg_, static_cast<unsigned>(std::__libcpp_ctz(__b)));
+      return _It(__first.__seg_, static_cast<unsigned>(std::__countr_zero(__b)));
     if (__n == __dn)
       return __first + __n;
     __n -= __dn;
@@ -115,14 +115,14 @@ __find_bool(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
   for (; __n >= __bits_per_word; ++__first.__seg_, __n -= __bits_per_word) {
     __storage_type __b = std::__invert_if<!_ToFind>(*__first.__seg_);
     if (__b)
-      return _It(__first.__seg_, static_cast<unsigned>(std::__libcpp_ctz(__b)));
+      return _It(__first.__seg_, static_cast<unsigned>(std::__countr_zero(__b)));
   }
   // do last partial word
   if (__n > 0) {
     __storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
     __storage_type __b = std::__invert_if<!_ToFind>(*__first.__seg_) & __m;
     if (__b)
-      return _It(__first.__seg_, static_cast<unsigned>(std::__libcpp_ctz(__b)));
+      return _It(__first.__seg_, static_cast<unsigned>(std::__countr_zero(__b)));
   }
   return _It(__first.__seg_, static_cast<unsigned>(__n));
 }
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.find/find.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.find/find.pass.cpp
index c32abce720468..e9fd8c17b40cb 100644
--- a/libcxx/test/std/algorithms/alg.nonmodifying/alg.find/find.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/alg.find/find.pass.cpp
@@ -17,7 +17,6 @@
 // ADDITIONAL_COMPILE_FLAGS(cl-style-warnings): /wd4245 /wd4305 /wd4310 /wd4389 /wd4805
 // ADDITIONAL_COMPILE_FLAGS(has-fconstexpr-steps): -fconstexpr-steps=20000000
 // ADDITIONAL_COMPILE_FLAGS(has-fconstexpr-ops-limit): -fconstexpr-ops-limit=80000000
-// XFAIL: FROZEN-CXX03-HEADERS-FIXME
 
 // <algorithm>