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authorkwolekr <kwolekr@minetest.net>2015-11-01 11:16:18 -0500
committerkwolekr <kwolekr@minetest.net>2015-11-01 11:16:18 -0500
commitd198e420ec54be47fe2285b3205953282ec06742 (patch)
tree9cb8f150ebb0c84b3db5f86e70ee7aad2be01f3d /src
parent9269a0ecc7267822bc5ac5af95ad4977bdc94fec (diff)
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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.
Diffstat (limited to 'src')
-rw-r--r--src/noise.cpp8
1 files 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;
}