From cbc229081a9df67a577b4bea61ad6aac52d470cb Mon Sep 17 00:00:00 2001 From: Ariya Hidayat Date: Tue, 30 Jun 2009 11:18:03 +0200 Subject: Faster quaternion multiplications. Use the known factorization trick to speed-up quaternion multiplication. Now we need only 9 floating-point multiplications, instead of 16 (but at the cost of extra additions and subtractions). Callgrind shows that the function now takes 299 instructions instead of 318 instructions, which is not a big win. However I assume the speed-up has a better effect for mobile CPU, where multiplications are more expensive. Reviewed-by: Rhys Weatherley --- src/gui/math3d/qquaternion.h | 29 +++++++++++------------------ 1 file changed, 11 insertions(+), 18 deletions(-) diff --git a/src/gui/math3d/qquaternion.h b/src/gui/math3d/qquaternion.h index 55c871d..9a1b590 100644 --- a/src/gui/math3d/qquaternion.h +++ b/src/gui/math3d/qquaternion.h @@ -198,24 +198,17 @@ inline QQuaternion &QQuaternion::operator*=(qreal factor) inline const QQuaternion operator*(const QQuaternion &q1, const QQuaternion& q2) { - // Algorithm from: - // http://www.j3d.org/matrix_faq/matrfaq_latest.html#Q53 - float x = q1.wp * q2.xp + - q1.xp * q2.wp + - q1.yp * q2.zp - - q1.zp * q2.yp; - float y = q1.wp * q2.yp + - q1.yp * q2.wp + - q1.zp * q2.xp - - q1.xp * q2.zp; - float z = q1.wp * q2.zp + - q1.zp * q2.wp + - q1.xp * q2.yp - - q1.yp * q2.xp; - float w = q1.wp * q2.wp - - q1.xp * q2.xp - - q1.yp * q2.yp - - q1.zp * q2.zp; + float ww = (q1.zp + q1.xp) * (q2.xp + q2.yp); + float yy = (q1.wp - q1.yp) * (q2.wp + q2.zp); + float zz = (q1.wp + q1.yp) * (q2.wp - q2.zp); + float xx = ww + yy + zz; + float qq = 0.5 * (xx + (q1.zp - q1.xp) * (q2.xp - q2.yp)); + + float w = qq - ww + (q1.zp - q1.yp) * (q2.yp - q2.zp); + float x = qq - xx + (q1.xp + q1.wp) * (q2.xp + q2.wp); + float y = qq - yy + (q1.wp - q1.xp) * (q2.yp + q2.zp); + float z = qq - zz + (q1.zp + q1.yp) * (q2.wp - q2.xp); + return QQuaternion(w, x, y, z, 1); } -- cgit v0.12