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Positive and negative zeros are possible in the floats, which are considered equal by the FP unit.

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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.
This commit is contained in:
bubnikv 2016-11-16 09:31:18 +01:00
parent 50f06a0fe8
commit d1d6e907c5
1 changed files with 37 additions and 0 deletions
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37
xs/src/admesh/stlinit.c
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@ -284,6 +284,20 @@ stl_read(stl_file *stl, int first_facet, int first) {
stl->error = 1;
return;
}
#if 0
// Report close to zero vertex coordinates. 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.
// It may be worth to round these numbers to zero during loading to reduce the number of errors reported
// during the STL import.
for (size_t j = 0; j < 3; ++ j) {
if (facet.vertex[j].x > -1e-12f && facet.vertex[j].x < 1e-12f)
printf("stl_read: facet %d.x = %e\r\n", j, facet.vertex[j].x);
if (facet.vertex[j].y > -1e-12f && facet.vertex[j].y < 1e-12f)
printf("stl_read: facet %d.y = %e\r\n", j, facet.vertex[j].y);
if (facet.vertex[j].z > -1e-12f && facet.vertex[j].z < 1e-12f)
printf("stl_read: facet %d.z = %e\r\n", j, facet.vertex[j].z);
}
#endif
} else
/* Read a single facet from an ASCII .STL file */
{
@ -304,6 +318,29 @@ stl_read(stl_file *stl, int first_facet, int first) {
return;
}
}
#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. */
stl->facet_start[i] = facet;