Fix UB in random generator

AMDmi3 · AJenbo · commit 04d0950c9e63 · 2022-05-18T04:40:54.000+02:00
abs(INT_MIN) is undefined behavior, so process this case without
calling abs()
diff --git a/Source/engine/random.cpp b/Source/engine/random.cpp
@@ -1,5 +1,7 @@
 #include "engine/random.hpp"
 
+#include <limits>
+
 #include "utils/stdcompat/abs.hpp"
 
 namespace devilution {
@@ -29,7 +31,9 @@ uint32_t GetLCGEngineState()
 
 int32_t GetRndSeed()
 {
-	return abs(static_cast<int32_t>(sglGameSeed));
+	const int32_t seed = static_cast<int32_t>(sglGameSeed);
+	// since abs(INT_MIN) is undefined behavior, handle this value specially
+	return seed == std::numeric_limits<int32_t>::min() ? std::numeric_limits<int32_t>::min() : abs(seed);
 }
 
 int32_t AdvanceRndSeed()

Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,7 @@`
`1`	`1`	`#include "engine/random.hpp"`
`2`	`2`
	`3`	`+#include <limits>`
	`4`	`+`
`3`	`5`	`#include "utils/stdcompat/abs.hpp"`
`4`	`6`
`5`	`7`	`namespace devilution {`
`@@ -29,7 +31,9 @@ uint32_t GetLCGEngineState()`
`29`	`31`
`30`	`32`	`int32_t GetRndSeed()`
`31`	`33`	`{`
`32`		`- return abs(static_cast<int32_t>(sglGameSeed));`
	`34`	`+ const int32_t seed = static_cast<int32_t>(sglGameSeed);`
	`35`	`+ // since abs(INT_MIN) is undefined behavior, handle this value specially`
	`36`	`+ return seed == std::numeric_limits<int32_t>::min() ? std::numeric_limits<int32_t>::min() : abs(seed);`
`33`	`37`	`}`
`34`	`38`
`35`	`39`	`int32_t AdvanceRndSeed()`