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| author | kwolekr <kwolekr@minetest.net> | 2015-11-01 11:16:18 -0500 |
|---|---|---|
| committer | kwolekr <kwolekr@minetest.net> | 2015-11-01 11:16:18 -0500 |
| commit | d198e420ec54be47fe2285b3205953282ec06742 (patch) | |
| tree | 9cb8f150ebb0c84b3db5f86e70ee7aad2be01f3d | |
| parent | 9269a0ecc7267822bc5ac5af95ad4977bdc94fec (diff) | |
| download | minetest-d198e420ec54be47fe2285b3205953282ec06742.tar.gz minetest-d198e420ec54be47fe2285b3205953282ec06742.tar.bz2 minetest-d198e420ec54be47fe2285b3205953282ec06742.zip | |
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.
| -rw-r--r-- | src/noise.cpp | 8 |
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; } |