Update Reference section

doc/hash/reference.adoc

@@ -142,9 +142,9 @@ template<class T> struct hash
 std::size_t operator()( T const& v ) const;
 ----
 
-Returns: :: `hash_value( v )`.
+Returns: :: `hash_value(v)`.
 
-Throws: :: Only throws if `hash_value( v )` throws.
+Throws: :: Only throws if `hash_value(v)` throws.
 
 Remarks: :: The call to `hash_value` is unqualified, so that user-supplied
   overloads will be found via argument dependent lookup.
@@ -159,44 +159,59 @@ template<class T> void hash_combine( std::size_t& seed, T const& v );
 Called repeatedly to incrementally create a hash value from several variables.
 
 Effects: :: Updates `seed` with a new hash value generated by
-  deterministically combining it with the result of `boost::hash<T>()( v )`.
+  deterministically combining it with the result of `boost::hash<T>()(v)`.
 
-Throws: :: Only throws if `boost::hash<T>()( v )` throws. On exception,
+Throws: :: Only throws if `boost::hash<T>()(v)` throws. On exception,
   `seed` is not updated.
 
 Remarks: ::
 +
 --
-Equivalent to `seed = combine( seed, boost::hash<T>()( v ) )`,
+Equivalent to `seed = combine(seed, boost::hash<T>()(v))`,
 where `combine(s, v)` is a mixing function that takes two arguments of
 type `std::size_t` and returns `std::size_t`, with the following desirable
 properties:
   
-* For a constant `s`, when `v` takes all possible `size_t` values,
+. For a constant `s`, when `v` takes all possible `size_t` values,
   `combine(s, v)` should also take all possible `size_t` values, producing
   a sequence that is close to random; that is, it should be a random
   permutation.
 +
 This guarantees that for a given `seed`, `combine` does not introduce
-hash collisions when none were produced by `boost::hash<T>( v )`. It
+hash collisions when none were produced by `boost::hash<T>(v)`; that is,
-also implies that `combine(s, v)`, as a function of `v`, has good avalanche
+it does not lose information from the input. It also implies that
-properties; that is, small (e.g. single bit) perturbations in the input `v`
+`combine(s, v)`, as a function of `v`, has good avalanche properties;
-lead to large perturbations in the return value (half of the output bits
+that is, small (e.g. single bit) perturbations in the input `v` lead to
-changing, on average).
+large perturbations in the return value (half of the output bits changing,
+on average).
 
-* For two different seeds `s1` and `s2`, `combine(s1, v)` and
+. For two different seeds `s1` and `s2`, `combine(s1, v)` and
   `combine(s2, v)`, treated as functions of `v`, should produce two
   different random permutations.
 
-* `combine(0, 0)` should not be 0. Since a common initial value of `seed`
+. `combine(0, 0)` should not be 0. Since a common initial value of `seed`
   is zero, `combine(0, 0) == 0` would imply that applying `hash_combine` on
   any sequence of zeroes, regardless of length, will produce zero. This is
   undesirable, as it would lead to e.g. `std::vector<int>()` and
   `std::vector<int>(4)` to have the same hash value.
 
 The current implementation uses the function `mix(s + 0x9e3779b9 + v)` as
-`combine(s, v)`, where `mix` is a high quality random permutation over the
+`combine(s, v)`, where `mix(x)` is a high quality mixing function that is a
-`std::size_t` values (with the property that `mix(0)` is 0).
+bijection over the `std::size_t` values, of the form
+
+[source]
+----
+x ^= x >> k1;
+x *= m1;
+x ^= x >> k2;
+x *= m2;
+x ^= x >> k3;
+----
+
+where the constants `k1`, `k2`, `k3`, `m1`, `m2` are suitably chosen.
+
+Note that `mix(0)` is 0. This is why we add the arbitrary constant
+`0x9e3779b9` to meet the third requirement above.
 --
 
 === hash_range
@@ -208,14 +223,23 @@ template<class It> void hash_range( std::size_t& seed, It first, It last );
 
 Effects: ::
 +
+--
+When `typename std::iterator_traits<It>::value_type` is not `char`, `signed char`,
+`unsigned char`,
+
 [source]
 ----
 for( ; first != last; ++first )
 {
-    hash_combine<typename std::iterator_traits<It>::value_type>( seed, *first );
+    boost::hash_combine<typename std::iterator_traits<It>::value_type>( seed, *first );
 }
 ----
 
+Otherwise, bytes from `[first, last)` are coalesced in an unspecified manner
+and then passed to `hash_combine`, more than one at a time. This is done in
+order to improve performance when hashing strings.
+--
+
 [source]
 ----
 template<class It> std::size_t hash_range( It first, It last );
@@ -226,7 +250,7 @@ Effects: ::
 [source]
 ----
 size_t seed = 0;
-hash_range( seed, first, last );
+boost::hash_range( seed, first, last );
 return seed;
 ----
 
@@ -238,7 +262,7 @@ template<class It> void hash_unordered_range( std::size_t& seed, It first, It la
 ----
 
 Effects: :: Updates `seed` with the values of
-  `boost::hash<typename std::iterator_traits<It>::value_type>()( *i )`
+  `boost::hash<typename std::iterator_traits<It>::value_type>()(*i)`
   for each `i` in `[first, last)`, such that the order of elements does
   not affect the final result.
 
@@ -252,7 +276,7 @@ Effects: ::
 [source]
 ----
 size_t seed = 0;
-hash_unordered_range( seed, first, last );
+boost::hash_unordered_range( seed, first, last );
 return seed;
 ----
 
@@ -282,7 +306,7 @@ Returns: ::
 `static_cast<std::size_t>(v)`.
 
 Remarks: ::
-`hash_value( std::to_underlying(v) )` would be better, but {cpp}03
+`hash_value(std::to_underlying(v))` would be better, but {cpp}03
 compatibility mandates the current implementation.
 
 [source]
@@ -315,7 +339,7 @@ template<class T, std::size_t N>
 ----
 
 Returns: ::
-`hash_range( v, v + N )`.
+`boost::hash_range( v, v + N )`.
 
 [source]
 ----
@@ -384,7 +408,7 @@ template<class T>
 ----
 
 Returns: ::
-`hash_range( v.begin(), v.end() )`.
+`boost::hash_range( v.begin(), v.end() )`.
 
 Remarks: ::
 This overload is only enabled when
@@ -402,7 +426,7 @@ template<class T>
 ----
 
 Returns: ::
-`hash_range( v.data(), v.data() + v.size() )`.
+`boost::hash_range( v.data(), v.data() + v.size() )`.
 
 Remarks: ::
 This overload handles all standard contiguous containers, such as
@@ -416,7 +440,7 @@ template<class T>
 ----
 
 Returns: ::
-`hash_unordered_range( v.begin(), v.end() )`.
+`boost::hash_unordered_range( v.begin(), v.end() )`.
 
 Remarks: ::
 This overload handles the standard unordered containers, such as
@@ -432,7 +456,7 @@ template<class T, class D>
 ----
 
 Returns: ::
-`hash<T*>( v.get() )`.
+`boost::hash<T*>( v.get() )`.
 
 [source]
 ----
@@ -468,7 +492,7 @@ template<class T>
 
 Returns: ::
 For a disengaged `v`, an unspecified constant value; otherwise,
-`hash<T>()( *v )`.
+`boost::hash<T>()( *v )`.
 
 [source]
 ----