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| author | Krzysztof Kosi??ski <tweenk.pl@gmail.com> | 2015-07-04 15:25:59 +0000 |
|---|---|---|
| committer | Krzysztof Kosiński <tweenk.pl@gmail.com> | 2015-07-04 15:25:59 +0000 |
| commit | 60437ac397d41678daba5daece227240e8ddd364 (patch) | |
| tree | 31f18c8296ffde9122492b46623375fc98585b17 /src/2geom/polynomial.cpp | |
| parent | 2Geom CMake adjustment (diff) | |
| download | inkscape-60437ac397d41678daba5daece227240e8ddd364.tar.gz inkscape-60437ac397d41678daba5daece227240e8ddd364.zip | |
Upgrade to 2Geom r2413
(bzr r14059.2.18)
Diffstat (limited to 'src/2geom/polynomial.cpp')
| -rw-r--r-- | src/2geom/polynomial.cpp | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/src/2geom/polynomial.cpp b/src/2geom/polynomial.cpp index a0689f0c5..ca2389f80 100644 --- a/src/2geom/polynomial.cpp +++ b/src/2geom/polynomial.cpp @@ -34,6 +34,7 @@ #include <algorithm> #include <2geom/polynomial.h> +#include <2geom/math-utils.h> #include <math.h> #ifdef HAVE_GSL @@ -235,12 +236,17 @@ std::vector<Coord> solve_quadratic(Coord a, Coord b, Coord c) if (delta == 0) { // one root - result.push_back(-0.5 * b / a); + result.push_back(-b / (2*a)); } else if (delta > 0) { // two roots Coord delta_sqrt = sqrt(delta); - result.push_back((-b + delta_sqrt)/(2*a)); - result.push_back((-b - delta_sqrt)/(2*a)); + + // Use different formulas depending on sign of b to preserve + // numerical stability. See e.g.: + // http://people.csail.mit.edu/bkph/articles/Quadratics.pdf + Coord t = -0.5 * (b + sgn(b) * delta_sqrt); + result.push_back(t / a); + result.push_back(c / t); } // no roots otherwise |