From d198e420ec54be47fe2285b3205953282ec06742 Mon Sep 17 00:00:00 2001
From: kwolekr <kwolekr@minetest.net>
Date: Sun, 1 Nov 2015 11:16:18 -0500
Subject: [PATCH] Fix Noise compiled under clang >= 3.7.x with -O2 or higher
When compiled with optimizations, the most recent versions of clang seem
to 'optimize' out a crucial "and %reg, 0x7FFFFFFF" instruction in noise2d(),
probably because it somehow assumed the variable n would never become greater
than that amount.
Indeed, signed integer underflow is undefined behavior in C and C++, so while
this optimization is "correct" in that sense, it breaks lots of existing code.
Solved by changing n to an unsigned type, making behavior well-defined.
---
src/noise.cpp | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/src/noise.cpp b/src/noise.cpp
index 2948fb765..b1b702538 100644
--- a/src/noise.cpp
+++ b/src/noise.cpp
@@ -158,21 +158,21 @@ s32 PcgRandom::randNormalDist(s32 min, s32 max, int num_trials)
float noise2d(int x, int y, int seed)
{
- int n = (NOISE_MAGIC_X * x + NOISE_MAGIC_Y * y
+ unsigned int n = (NOISE_MAGIC_X * x + NOISE_MAGIC_Y * y
+ NOISE_MAGIC_SEED * seed) & 0x7fffffff;
n = (n >> 13) ^ n;
n = (n * (n * n * 60493 + 19990303) + 1376312589) & 0x7fffffff;
- return 1.f - (float)n / 0x40000000;
+ return 1.f - (float)(int)n / 0x40000000;
}
float noise3d(int x, int y, int z, int seed)
{
- int n = (NOISE_MAGIC_X * x + NOISE_MAGIC_Y * y + NOISE_MAGIC_Z * z
+ unsigned int n = (NOISE_MAGIC_X * x + NOISE_MAGIC_Y * y + NOISE_MAGIC_Z * z
+ NOISE_MAGIC_SEED * seed) & 0x7fffffff;
n = (n >> 13) ^ n;
n = (n * (n * n * 60493 + 19990303) + 1376312589) & 0x7fffffff;
- return 1.f - (float)n / 0x40000000;
+ return 1.f - (float)(int)n / 0x40000000;
}
--
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