SCI: Fixed bug #3413020 - "SCI: Longbow: Robin is stuck in the final monk chase scene"

Special thanks to wjp for his work on bisecting to find the regression and
for checking against the KQ5CD disasm

1 files changed, 8 insertions, 0 deletions

diff --git a/engines/sci/engine/kmath.cpp b/engines/sci/engine/kmath.cpp
index ef795d7e2f..7570856dff 100644
--- a/engines/sci/engine/kmath.cpp
+++ b/engines/sci/engine/kmath.cpp
@@ -37,6 +37,14 @@ reg_t kRandom(EngineState *s, int argc, reg_t *argv) {
 		//  some codes in sq4 are also random and 5 digit (if i remember correctly)
 		const uint16 fromNumber = argv[0].toUint16();
 		const uint16 toNumber = argv[1].toUint16();
+		// Some scripts may request a range in the reverse order (from largest
+		// to smallest). An example can be found in Longbow, room 710, where a
+		// random number is requested from 119 to 83. In this case, we're
+		// supposed to return toNumber (determined by the KQ5CD disasm).
+		// Fixes bug #3413020.
+		if (fromNumber > toNumber)
+			return make_reg(0, toNumber);
+
 		uint16 range = toNumber - fromNumber + 1;
 		// calculating range is exactly how sierra sci did it and is required for hoyle 4
 		//  where we get called with kRandom(0, -1) and we are supposed to give back values from 0 to 0