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Work around overflow in distance calculations

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Erica Fischer
2024-03-18 12:47:07 -07:00
parent 686ab56c4a
commit 5dd72da3f8
1 changed files with 16 additions and 16 deletions
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geometry.cpp
+16 -16
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@@ -301,8 +301,8 @@ bool point_within_tile(long long x, long long y, int z) {
} }
double distance_from_line(long long point_x, long long point_y, long long segA_x, long long segA_y, long long segB_x, long long segB_y) { double distance_from_line(long long point_x, long long point_y, long long segA_x, long long segA_y, long long segB_x, long long segB_y) {
long long p2x = segB_x - segA_x; __int128 p2x = segB_x - segA_x;
long long p2y = segB_y - segA_y; __int128 p2y = segB_y - segA_y;
// These calculations must be made in integers instead of floating point // These calculations must be made in integers instead of floating point
// to make them consistent between x86 and arm floating point implementations. // to make them consistent between x86 and arm floating point implementations.
@@ -311,7 +311,7 @@ double distance_from_line(long long point_x, long long point_y, long long segA_x
// making their sum up to 69 bits. Downshift before multiplying to keep them in range. // making their sum up to 69 bits. Downshift before multiplying to keep them in range.
double something = ((p2x / 4) * (p2x / 8) + (p2y / 4) * (p2y / 8)) * 32.0; double something = ((p2x / 4) * (p2x / 8) + (p2y / 4) * (p2y / 8)) * 32.0;
// likewise // likewise
double u = (0 == something) ? 0 : ((point_x - segA_x) / 4 * (p2x / 8) + (point_y - segA_y) / 4 * (p2y / 8)) * 32.0 / (something); double u = (0 == something) ? 0 : ((__int128) (point_x - segA_x) / 4 * (p2x / 8) + (__int128) (point_y - segA_y) / 4 * (p2y / 8)) * 32.0 / (something);
if (u >= 1) { if (u >= 1) {
u = 1; u = 1;
@@ -671,9 +671,9 @@ drawvec fix_polygon(const drawvec &geom) {
// calculate centroid // calculate centroid
// a + 1 < size() because point 0 is duplicated at the end // a + 1 < size() because point 0 is duplicated at the end
long long xtotal = 0; __int128 xtotal = 0;
long long ytotal = 0; __int128 ytotal = 0;
long long count = 0; size_t count = 0;
for (size_t a = 0; a + 1 < ring.size(); a++) { for (size_t a = 0; a + 1 < ring.size(); a++) {
xtotal += ring[a].x; xtotal += ring[a].x;
ytotal += ring[a].y; ytotal += ring[a].y;
@@ -683,13 +683,13 @@ drawvec fix_polygon(const drawvec &geom) {
ytotal /= count; ytotal /= count;
// figure out which point is furthest from the centroid // figure out which point is furthest from the centroid
long long dist2 = 0; __int128 dist2 = 0;
long long furthest = 0; size_t furthest = 0;
for (size_t a = 0; a + 1 < ring.size(); a++) { for (size_t a = 0; a + 1 < ring.size(); a++) {
// division by 16 because these are z0 coordinates and we need to avoid overflow // division by 16 because these are z0 coordinates and we need to avoid overflow
long long xd = (ring[a].x - xtotal) / 16; __int128 xd = (ring[a].x - xtotal) / 16;
long long yd = (ring[a].y - ytotal) / 16; __int128 yd = (ring[a].y - ytotal) / 16;
long long d2 = xd * xd + yd * yd; __int128 d2 = xd * xd + yd * yd;
if (d2 > dist2 || (d2 == dist2 && ring[a] < ring[furthest])) { if (d2 > dist2 || (d2 == dist2 && ring[a] < ring[furthest])) {
dist2 = d2; dist2 = d2;
furthest = a; furthest = a;
@@ -699,13 +699,13 @@ drawvec fix_polygon(const drawvec &geom) {
// then figure out which point is furthest from *that*, // then figure out which point is furthest from *that*,
// which will hopefully be a good origin point since it should be // which will hopefully be a good origin point since it should be
// at a far edge of the shape. // at a far edge of the shape.
long long dist2b = 0; __int128 dist2b = 0;
long long furthestb = 0; size_t furthestb = 0;
for (size_t a = 0; a + 1 < ring.size(); a++) { for (size_t a = 0; a + 1 < ring.size(); a++) {
// division by 16 because these are z0 coordinates and we need to avoid overflow // division by 16 because these are z0 coordinates and we need to avoid overflow
long long xd = (ring[a].x - ring[furthest].x) / 16; __int128 xd = (ring[a].x - ring[furthest].x) / 16;
long long yd = (ring[a].y - ring[furthest].y) / 16; __int128 yd = (ring[a].y - ring[furthest].y) / 16;
long long d2 = xd * xd + yd * yd; __int128 d2 = xd * xd + yd * yd;
if (d2 > dist2b || (d2 == dist2b && ring[a] < ring[furthestb])) { if (d2 > dist2b || (d2 == dist2b && ring[a] < ring[furthestb])) {
dist2b = d2; dist2b = d2;
furthestb = a; furthestb = a;