From ee78f1816172f35c86b97279c56d5cc672436572 Mon Sep 17 00:00:00 2001
From: Dmitry Arkhipov <grisumbras@yandex.ru>
Date: Wed, 11 Oct 2023 16:18:20 +0300
Subject: [PATCH] detail::stack grows by powers of 2

---
 include/boost/json/detail/impl/stack.hpp | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/include/boost/json/detail/impl/stack.hpp b/include/boost/json/detail/impl/stack.hpp
index e334e9fa2..058f0998c 100644
--- a/include/boost/json/detail/impl/stack.hpp
+++ b/include/boost/json/detail/impl/stack.hpp
@@ -46,15 +46,25 @@ reserve_impl(std::size_t n)
     // caller checks this
     BOOST_ASSERT(n > cap_);
 
-    if(BOOST_JSON_UNLIKELY( n > std::numeric_limits<std::size_t>::max() - n ))
+    constexpr std::size_t max = std::numeric_limits<std::size_t>::max();
+    std::size_t cap = cap_ ? cap_ : 32 ;
+    do
+    {
+        if(BOOST_JSON_UNLIKELY( cap > max - cap ))
+            throw_exception( std::bad_alloc(), BOOST_CURRENT_LOCATION );
+        cap *= 2;
+    }
+    while(cap < n);
+
+    if(BOOST_JSON_UNLIKELY( cap > max - cap ))
         throw_exception( std::bad_alloc(), BOOST_CURRENT_LOCATION );
 
-    auto const base = static_cast<unsigned char*>( sp_->allocate(n * 2) );
+    auto const base = static_cast<unsigned char*>( sp_->allocate(cap * 2) );
     if(base_)
     {
         // copy trivials
         if(size1_ > 0)
-            std::memcpy(base + n - size1_, base_ + cap_ - size1_, size1_);
+            std::memcpy(base + cap - size1_, base_ + cap_ - size1_, size1_);
 
         // copy non-trivials
         if(head_)
@@ -85,7 +95,7 @@ reserve_impl(std::size_t n)
             sp_->deallocate(base_, cap_ * 2);
     }
     base_ = base;
-    cap_ = n;
+    cap_ = cap;
 }
 
 template<class T>