From 4c9827278720205f921928bb37fd57edde49d46b Mon Sep 17 00:00:00 2001
From: Dmitry Arkhipov <grisumbras@gmail.com>
Date: Sun, 8 Aug 2021 07:19:41 +0300
Subject: [PATCH 1/3] calculate digest in batches

This is intended to increase performance
---
 include/boost/json/detail/digest.hpp | 40 +++++++++++++++++++++++-----
 1 file changed, 34 insertions(+), 6 deletions(-)

diff --git a/include/boost/json/detail/digest.hpp b/include/boost/json/detail/digest.hpp
index 2d9465c00..49a823b32 100644
--- a/include/boost/json/detail/digest.hpp
+++ b/include/boost/json/detail/digest.hpp
@@ -10,6 +10,10 @@
 #ifndef BOOST_JSON_DETAIL_DIGEST_HPP
 #define BOOST_JSON_DETAIL_DIGEST_HPP
 
+#include <algorithm>
+#include <array>
+#include <cstring>
+
 namespace boost {
 namespace json {
 namespace detail {
@@ -23,15 +27,39 @@ digest(
     std::size_t salt) noexcept
 {
 #if BOOST_JSON_ARCH == 64
-    std::uint64_t const prime = 0x100000001B3ULL;
-    std::uint64_t hash  = 0xcbf29ce484222325ULL;
+    using hash_t = std::uint64_t;
+    hash_t const prime = 0x100000001B3ULL;
+    hash_t hash  = 0xcbf29ce484222325ULL;
 #else
-    std::uint32_t const prime = 0x01000193UL;
-    std::uint32_t hash  = 0x811C9DC5UL;
+    using hash_t = std::uint32_t;
+    hash_t const prime = 0x01000193UL;
+    hash_t hash  = 0x811C9DC5UL;
 #endif
     hash += salt;
-    for(; b != e; ++b)
-        hash = (*b ^ hash) * prime;
+
+    constexpr std::size_t step = sizeof(hash_t);
+    std::size_t n = std::distance(b, e);
+    std::size_t const m = n % step;
+
+    char temp[step];
+    hash_t batch;
+    while( n > m )
+    {
+        std::copy_n(b, step, temp);
+
+        std::memcpy(&batch, temp, step);
+        hash = (batch ^ hash) * prime;
+
+        std::advance(b, step);
+        n -= step;
+    }
+
+    std::memset(temp, 0, step);
+    std::copy_n(b, n, temp);
+
+    std::memcpy(&batch, temp, step);
+    hash = (batch ^ hash) * prime;
+
     return hash;
 }
 

From 699a2e4d5eea7b611cd5b349e559d3fc150a7ccd Mon Sep 17 00:00:00 2001
From: Dmitry Arkhipov <grisumbras@yandex.ru>
Date: Fri, 16 Jun 2023 17:36:29 +0300
Subject: [PATCH 2/3] temp

---
 include/boost/json/detail/digest.hpp | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/boost/json/detail/digest.hpp b/include/boost/json/detail/digest.hpp
index 49a823b32..94d318df5 100644
--- a/include/boost/json/detail/digest.hpp
+++ b/include/boost/json/detail/digest.hpp
@@ -41,23 +41,23 @@ digest(
     std::size_t n = std::distance(b, e);
     std::size_t const m = n % step;
 
-    char temp[step];
+    std::array<unsigned char, step> temp;
     hash_t batch;
     while( n > m )
     {
-        std::copy_n(b, step, temp);
+        std::copy_n(b, step, temp.data());
 
-        std::memcpy(&batch, temp, step);
+        std::memcpy(&batch, temp.data(), step);
         hash = (batch ^ hash) * prime;
 
         std::advance(b, step);
         n -= step;
     }
 
-    std::memset(temp, 0, step);
-    std::copy_n(b, n, temp);
+    temp.fill(0);
+    std::copy_n(b, n, temp.data());
 
-    std::memcpy(&batch, temp, step);
+    std::memcpy(&batch, temp.data(), step);
     hash = (batch ^ hash) * prime;
 
     return hash;

From c2915984ce1fd30284c6912edb3963ec76b638e8 Mon Sep 17 00:00:00 2001
From: Dmitry Arkhipov <grisumbras@yandex.ru>
Date: Mon, 19 Jun 2023 18:30:35 +0300
Subject: [PATCH 3/3] temp2

---
 include/boost/json/detail/digest.hpp | 40 ++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/include/boost/json/detail/digest.hpp b/include/boost/json/detail/digest.hpp
index 94d318df5..3fb8a70d7 100644
--- a/include/boost/json/detail/digest.hpp
+++ b/include/boost/json/detail/digest.hpp
@@ -39,11 +39,10 @@ digest(
 
     constexpr std::size_t step = sizeof(hash_t);
     std::size_t n = std::distance(b, e);
-    std::size_t const m = n % step;
 
     std::array<unsigned char, step> temp;
     hash_t batch;
-    while( n > m )
+    while( n >= step )
     {
         std::copy_n(b, step, temp.data());
 
@@ -63,6 +62,43 @@ digest(
     return hash;
 }
 
+// Calculate salted digest of string
+template<>
+inline
+std::size_t
+digest<char const*>(
+    char const* b,
+    char const* e,
+    std::size_t salt) noexcept
+{
+#if BOOST_JSON_ARCH == 64
+    using hash_t = std::uint64_t;
+    hash_t const prime = 0x100000001B3ULL;
+    hash_t hash  = 0xcbf29ce484222325ULL;
+#else
+    using hash_t = std::uint32_t;
+    hash_t const prime = 0x01000193UL;
+    hash_t hash  = 0x811C9DC5UL;
+#endif
+    hash += salt;
+
+    constexpr std::size_t step = sizeof(hash_t);
+
+    hash_t batch;
+    for( ; (e - b) >= static_cast<int>(step); b += step )
+    {
+        std::memcpy(&batch, b, step);
+        hash = (batch ^ hash) * prime;
+    }
+
+    batch = 0;
+    std::memcpy(&batch, b, e - b);
+    hash = (batch ^ hash) * prime;
+
+    return hash;
+}
+
+
 } // detail
 } // namespace json
 } // namespace boost