From d198e420ec54be47fe2285b3205953282ec06742 Mon Sep 17 00:00:00 2001 From: kwolekr 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; } -- 2.25.1