Reverted unification of positive and negative zeros when loaded

from an STL file.

Conflicts:

	xs/src/admesh/stlinit.c

xs/src/admesh/stlinit.c

@@ -318,6 +318,28 @@ stl_read(stl_file *stl, int first_facet, int first) {
       }
 #endif
 
+#if 1
+    {
+      // Positive and negative zeros are possible in the floats, which are considered equal by the FP unit.
+      // When using a memcmp on raw floats, those numbers report to be different.
+      // Unify all +0 and -0 to +0 to make the floats equal under memcmp.
+      uint32_t *f = (uint32_t*)&facet;
+      for (int j = 0; j < 12; ++ j, ++ f) // 3x vertex + normal: 4x3 = 12 floats
+        if (*f == 0x80000000)
+          // Negative zero, switch to positive zero.
+          *f = 0;
+    }
+#else
+    {
+      // Due to the nature of the floating point numbers, close to zero values may be represented with singificantly higher precision 
+      // than the rest of the vertices. Round them to zero.
+      float *f = (float*)&facet;
+      for (int j = 0; j < 12; ++ j, ++ f) // 3x vertex + normal: 4x3 = 12 floats
+        if (*f > -1e-12f && *f < 1e-12f)
+          // Negative zero, switch to positive zero.
+          *f = 0;
+    }
+#endif
     /* Write the facet into memory. */
     memcpy(stl->facet_start+i, &facet, SIZEOF_STL_FACET);
     stl_facet_stats(stl, facet, first);