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Fix: [Blitter] Avoid signed overflow when drawing long lines

This commit is contained in:
Jonathan G Rennison 2018-01-17 02:34:03 +00:00 committed by PeterN
parent db924a4681
commit 0240e90169
1 changed files with 2 additions and 2 deletions
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4
src/blitter/common.hpp
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@ -50,11 +50,11 @@ void Blitter::DrawLineGeneric(int x, int y, int x2, int y2, int screen_width, in
/* compute frac_diff = width * sqrt(dx*dx + dy*dy)
* Start interval:
* max(dx, dy) <= sqrt(dx*dx + dy*dy) <= sqrt(2) * max(dx, dy) <= 3/2 * max(dx, dy) */
int frac_sq = width * width * (dx * dx + dy * dy);
int64 frac_sq = ((int64) width) * ((int64) width) * (((int64) dx) * ((int64) dx) + ((int64) dy) * ((int64) dy));
int frac_max = 3 * frac_diff / 2;
while (frac_diff < frac_max) {
int frac_test = (frac_diff + frac_max) / 2;
if (frac_test * frac_test < frac_sq) {
if (((int64) frac_test) * ((int64) frac_test) < frac_sq) {
frac_diff = frac_test + 1;
} else {
frac_max = frac_test - 1;