prevector::swap: fix (unreached) data corruption

random-zebra · random-zebra · commit 035760e417bb · 2020-05-17T15:19:07.000+02:00
swap was using an incorrect condition to determine when to apply an optimization (not swapping the full direct[] when swapping two indirect prevectors). Rather than correct the optimization I'm removing it for simplicity. Removing this optimization minutely improves performance in the typical (currently only) usage of member swap(), which is swapping with a freshly value-initialized object. backports bitcoin/bitcoin@a7af72a
diff --git a/src/prevector.h b/src/prevector.h
@@ -412,12 +412,7 @@ class prevector {
     }
 
     void swap(prevector<N, T, Size, Diff>& other) {
-        if (_size & other._size & 1) {
-            std::swap(_union.capacity, other._union.capacity);
-            std::swap(_union.indirect, other._union.indirect);
-        } else {
-            std::swap(_union, other._union);
-        }
+        std::swap(_union, other._union);
         std::swap(_size, other._size);
     }
 

Original file line number	Diff line number	Diff line change
`@@ -412,12 +412,7 @@ class prevector {`
`412`	`412`	`}`
`413`	`413`
`414`	`414`	`void swap(prevector<N, T, Size, Diff>& other) {`
`415`		`- if (_size & other._size & 1) {`
`416`		`- std::swap(_union.capacity, other._union.capacity);`
`417`		`- std::swap(_union.indirect, other._union.indirect);`
`418`		`- } else {`
`419`		`- std::swap(_union, other._union);`
`420`		`- }`
	`415`	`+ std::swap(_union, other._union);`
`421`	`416`	`std::swap(_size, other._size);`
`422`	`417`	`}`
`423`	`418`