Merge pull request 'add jetbrains sponsor' (#360) from wowario/wownero:jetbrains into master

Reviewed-on: https://git.wownero.com/wownero/wownero/pulls/360

README.md

@@ -41,6 +41,9 @@ Wownero is a 100% community-sponsored endeavor. Supporting services are also gra
 [<img src="https://git.wownero.com/wownero/meta/raw/branch/master/images/macstadium.png"
       alt="MacStadium"
       height="100">](https://www.macstadium.com)
+[<img src="https://git.wownero.com/wownero/meta/raw/branch/master/images/jetbrains.png"
+      alt="JetBrains"
+      height="100">](https://www.jetbrains.com)
 
 Developers are volunteers doing this mostly for shits and giggles. If you would like to support our shenanigans and stimulant addictions, please consider donating to [WFS proposals](https://funding.wownero.com/proposals) or the dev slush fund.
 

src/cryptonote_basic/difficulty.cpp

@@ -389,7 +389,7 @@ namespace cryptonote {
     avg_D = static_cast<uint64_t>(( cumulative_difficulties[N] - cumulative_difficulties[0] )/ N);
 
     // Prevent round off error for small D and overflow for large D.
-    if (avg_D > 2000000*N*N*T) {
+    if (avg_D > uint64_t(-1)/(N*(N+1)*T*99)) {
       next_D = (avg_D/(200*L))*(N*(N+1)*T*99);
     }
     else {    next_D = (avg_D*N*(N+1)*T*99)/(200*L);    }