Fix Lua PcgRandom

Before, this lua code led to a crash:

local pcg = PcgRandom(42)
local value = pcg:next()

This was because if you called s32 PcgRandom::range(min, max) with the
minimum and maximum possible values for s32 integers (which the lua
binding code did), u32 PcgRandom::range(bound) got called with 0 as the
bound. The bound however is one above the maximum value, so 0 is a "special"
value to pass to this function. This commit fixes the lua crash by
assigning the RNG's full range to the bound 0, which is also fits to the
"maximum is bound - 1" principle, as (u32)-1 is the maximum value in the
u32 range.

2 files changed, 6 insertions, 0 deletions

diff --git a/src/noise.cpp b/src/noise.cpp
index 443c405ce..2948fb765 100644
--- a/src/noise.cpp
+++ b/src/noise.cpp
@@ -90,6 +90,9 @@ u32 PcgRandom::next()
 
 u32 PcgRandom::range(u32 bound)
 {
+	// If the bound is 0, we cover the whole RNG's range
+	if (bound == 0)
+		return next();
 	/*
 	If the bound is not a multiple of the RNG's range, it may cause bias,
 	e.g. a RNG has a range from 0 to 3 and we take want a number 0 to 2.
diff --git a/src/unittest/test_random.cpp b/src/unittest/test_random.cpp
index 20cfca334..bbee57719 100644
--- a/src/unittest/test_random.cpp
+++ b/src/unittest/test_random.cpp
@@ -101,6 +101,9 @@ void TestRandom::testPcgRandomRange()
 
 	EXCEPTION_CHECK(PrngException, pr.range(5, 1));
 
+	// Regression test for bug 3027
+	pr.range(pr.RANDOM_MIN, pr.RANDOM_MAX);
+
 	for (u32 i = 0; i != 32768; i++) {
 		int min = (pr.next() % 3000) - 500;
 		int max = (pr.next() % 3000) - 500;