From c07630ac60f5d9555773953debf7c015cce1c902 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Thu, 2 Feb 2023 04:09:54 +0200
Subject: [PATCH] Add read32le to detail/hash_range.hpp

---
 .../container_hash/detail/hash_range.hpp      | 101 ++++++------------
 1 file changed, 31 insertions(+), 70 deletions(-)

diff --git a/include/boost/container_hash/detail/hash_range.hpp b/include/boost/container_hash/detail/hash_range.hpp
index 4583ab4..2d5ae52 100644
--- a/include/boost/container_hash/detail/hash_range.hpp
+++ b/include/boost/container_hash/detail/hash_range.hpp
@@ -38,6 +38,8 @@ template<> struct is_char_type<std::byte>: public boost::true_type {};
 
 #endif
 
+// generic version
+
 template<class It>
 inline typename boost::enable_if_<
     !is_char_type<typename std::iterator_traits<It>::value_type>::value,
@@ -52,6 +54,34 @@ std::size_t >::type
     return seed;
 }
 
+// specialized char[] version
+
+template<class It> inline boost::uint32_t read32le( It p )
+{
+    // clang 5+, gcc 5+ figure out this pattern and use a single mov on x86
+    // gcc on s390x and power BE even knows how to use load-reverse
+
+    boost::uint32_t w =
+        static_cast<boost::uint32_t>( static_cast<unsigned char>( p[0] ) ) |
+        static_cast<boost::uint32_t>( static_cast<unsigned char>( p[1] ) ) <<  8 |
+        static_cast<boost::uint32_t>( static_cast<unsigned char>( p[2] ) ) << 16 |
+        static_cast<boost::uint32_t>( static_cast<unsigned char>( p[3] ) ) << 24;
+
+    return w;
+}
+
+#if defined(_MSC_VER) && !defined(__clang__)
+
+template<class T> inline boost::uint32_t read32le( T* p )
+{
+    boost::uint32_t w;
+
+    std::memcpy( &w, p, 4 );
+    return w;
+}
+
+#endif
+
 template<class It>
 inline typename boost::enable_if_<
     is_char_type<typename std::iterator_traits<It>::value_type>::value &&
@@ -63,15 +93,7 @@ std::size_t>::type
 
     for( ; n >= 4; first += 4, n -= 4 )
     {
-        // clang 5+, gcc 5+ figure out this pattern and use a single mov on x86
-        // gcc on s390x and power BE even knows how to use load-reverse
-
-        boost::uint32_t w =
-            static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
-            static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) <<  8 |
-            static_cast<boost::uint32_t>( static_cast<unsigned char>( first[2] ) ) << 16 |
-            static_cast<boost::uint32_t>( static_cast<unsigned char>( first[3] ) ) << 24;
-
+        boost::uint32_t w = read32le( first );
         hash_combine( seed, w );
     }
 
@@ -117,67 +139,6 @@ std::size_t>::type
     return seed;
 }
 
-#if defined(_MSC_VER) && !defined(__clang__)
-
-template<class T>
-inline typename boost::enable_if_<is_char_type<T>::value, std::size_t>::type
-    hash_range( std::size_t seed, T const* first, T const* last )
-{
-    std::size_t n = static_cast<std::size_t>( last - first );
-
-    for( ; n >= 4; first += 4, n -= 4 )
-    {
-        boost::uint32_t w;
-
-        std::memcpy( &w, first, 4 );
-
-        hash_combine( seed, w );
-    }
-
-    {
-        // add a trailing suffix byte of 0x01 because otherwise sequences of
-        // trailing zeroes are indistinguishable from end of string
-
-        boost::uint32_t w = 0x01u;
-
-        switch( n )
-        {
-        case 1:
-
-            w =
-                static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
-                0x0100u;
-
-            break;
-
-        case 2:
-
-            w =
-                static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
-                static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) <<  8 |
-                0x010000u;
-
-            break;
-
-        case 3:
-
-            w =
-                static_cast<boost::uint32_t>( static_cast<unsigned char>( first[0] ) ) |
-                static_cast<boost::uint32_t>( static_cast<unsigned char>( first[1] ) ) <<  8 |
-                static_cast<boost::uint32_t>( static_cast<unsigned char>( first[2] ) ) << 16 |
-                0x01000000u;
-
-            break;
-        }
-
-        hash_combine( seed, w );
-    }
-
-    return seed;
-}
-
-#endif
-
 template<class It>
 inline typename boost::enable_if_<
     is_char_type<typename std::iterator_traits<It>::value_type>::value &&