PR 59406 note that FNV hash functions are incorrect

	PR libstdc++/59406
	* include/bits/functional_hash.h: Add comment noting difference from
	FNV-1a.
	* include/tr1/functional_hash.h: Likewise.
	* libsupc++/hash_bytes.cc: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@242454 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 6 insertions, 0 deletions

diff --git a/libstdc++-v3/libsupc++/hash_bytes.cc b/libstdc++-v3/libsupc++/hash_bytes.cc
index 1042de66388a..7d76c34edb40 100644
--- a/libstdc++-v3/libsupc++/hash_bytes.cc
+++ b/libstdc++-v3/libsupc++/hash_bytes.cc
@@ -112,6 +112,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   }
 
   // Implementation of FNV hash for 32-bit size_t.
+  // N.B. This function should work on unsigned char, otherwise it does not
+  // correctly implement the FNV-1a algorithm (see PR59406).
+  // The existing behaviour is retained for backwards compatibility.
   size_t
   _Fnv_hash_bytes(const void* ptr, size_t len, size_t hash)
   {
@@ -157,6 +160,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   }
 
   // Implementation of FNV hash for 64-bit size_t.
+  // N.B. This function should work on unsigned char, otherwise it does not
+  // correctly implement the FNV-1a algorithm (see PR59406).
+  // The existing behaviour is retained for backwards compatibility.
   size_t
   _Fnv_hash_bytes(const void* ptr, size_t len, size_t hash)
   {