Make explicit that we expect co-ordinates to be finite

The various spatial-vector, line, point, region and margin types have
all long taken for granted that their co-ordinates are finite and, in
particular, not NaN. Make this expectation explicit in the
documentation. Added assertions where (chiefly) noexcept and (where
the assertion would be a simple qIsFinite() call) constexpr didn't
preclude doing so. Also assert against zero divisors that would lead
to non-finite results.

Make minor clean-ups to docs in the process. QMarginsF had several
methods whose declaration, definition and docs weren't consistent in
their parameter names.

Task-number: QTBUG-89010
Change-Id: I601a830959d13a73dcb17ce31a1202a1486c8f7f
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

2 files changed, 111 insertions, 52 deletions

diff --git a/src/gui/math3d/qvectornd.cpp b/src/gui/math3d/qvectornd.cpp
index 1c456a9d6d..28e8f9ff67 100644
--- a/src/gui/math3d/qvectornd.cpp
+++ b/src/gui/math3d/qvectornd.cpp
@@ -56,6 +56,10 @@ QT_BEGIN_NAMESPACE
     \ingroup painting-3D
     \inmodule QtGui
 
+    Vectors are one of the main building blocks of 2D representation and
+    drawing. They consist of two finite floating-point coordinates,
+    traditionally called x and y.
+
     The QVector2D class can also be used to represent vertices in 2D space.
     We therefore do not need to provide a separate vertex class.
 
@@ -80,6 +84,7 @@ QT_BEGIN_NAMESPACE
     \fn QVector2D::QVector2D(float xpos, float ypos)
 
     Constructs a vector with coordinates (\a xpos, \a ypos).
+    Both coordinates must be finite.
 */
 
 /*!
@@ -146,7 +151,7 @@ QT_BEGIN_NAMESPACE
 /*!
     \fn void QVector2D::setX(float x)
 
-    Sets the x coordinate of this point to the given \a x coordinate.
+    Sets the x coordinate of this point to the given finite \a x coordinate.
 
     \sa x(), setY()
 */
@@ -154,7 +159,7 @@ QT_BEGIN_NAMESPACE
 /*!
     \fn void QVector2D::setY(float y)
 
-    Sets the y coordinate of this point to the given \a y coordinate.
+    Sets the y coordinate of this point to the given finite \a y coordinate.
 
     \sa y(), setX()
 */
@@ -260,7 +265,7 @@ QT_BEGIN_NAMESPACE
 /*!
     \fn QVector2D &QVector2D::operator*=(float factor)
 
-    Multiplies this vector's coordinates by the given \a factor, and
+    Multiplies this vector's coordinates by the given finite \a factor and
     returns a reference to this vector.
 
     \sa operator/=()
@@ -276,8 +281,8 @@ QT_BEGIN_NAMESPACE
 /*!
     \fn QVector2D &QVector2D::operator/=(float divisor)
 
-    Divides this vector's coordinates by the given \a divisor, and
-    returns a reference to this vector.
+    Divides this vector's coordinates by the given \a divisor and returns a
+    reference to this vector. The \a divisor must not be either zero or NaN.
 
     \sa operator*=()
 */
@@ -286,10 +291,12 @@ QT_BEGIN_NAMESPACE
     \fn QVector2D &QVector2D::operator/=(QVector2D vector)
     \since 5.5
 
-    Divides the components of this vector by the corresponding
-    components in \a vector.
+    Divides each component of this vector by the corresponding component of \a
+    vector and returns a reference to this vector.
 
-    \sa operator*=()
+    The \a vector must have no component that is either zero or NaN.
+
+    \sa operator*=(), operator/()
 */
 
 /*!
@@ -333,7 +340,7 @@ QT_BEGIN_NAMESPACE
 /*! //! friend
     \fn const QVector2D QVector2D::operator*(float factor, QVector2D vector)
 
-    Returns a copy of the given \a vector,  multiplied by the given \a factor.
+    Returns a copy of the given \a vector, multiplied by the given finite \a factor.
 
     \sa QVector2D::operator*=()
 */
@@ -341,7 +348,7 @@ QT_BEGIN_NAMESPACE
 /*! //! friend
     \fn const QVector2D QVector2D::operator*(QVector2D vector, float factor)
 
-    Returns a copy of the given \a vector,  multiplied by the given \a factor.
+    Returns a copy of the given \a vector, multiplied by the given finite \a factor.
 
     \sa QVector2D::operator*=()
 */
@@ -366,8 +373,10 @@ QT_BEGIN_NAMESPACE
 /*! //! friend
     \fn const QVector2D QVector2D::operator/(QVector2D vector, float divisor)
 
-    Returns the QVector2D object formed by dividing all three components of
-    the given \a vector by the given \a divisor.
+    Returns the QVector2D object formed by dividing each component of the given
+    \a vector by the given \a divisor.
+
+    The \a divisor must not be either zero or NaN.
 
     \sa QVector2D::operator/=()
 */
@@ -376,8 +385,10 @@ QT_BEGIN_NAMESPACE
     \fn const QVector2D QVector2D::operator/(QVector2D vector, QVector2D divisor)
     \since 5.5
 
-    Returns the QVector2D object formed by dividing components of the given
-    \a vector by a respective components of the given \a divisor.
+    Returns the QVector2D object formed by dividing each component of the given
+    \a vector by the corresponding component of the given \a divisor.
+
+    The \a divisor must have no component that is either zero or NaN.
 
     \sa QVector2D::operator/=()
 */
@@ -481,6 +492,7 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
     float x, y;
     stream >> x;
     stream >> y;
+    Q_ASSERT(qIsFinite(x) && qIsFinite(y));
     vector.setX(x);
     vector.setY(y);
     return stream;
@@ -502,8 +514,8 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
     \inmodule QtGui
 
     Vectors are one of the main building blocks of 3D representation and
-    drawing. They consist of three coordinates, traditionally called
-    x, y, and z.
+    drawing. They consist of three finite floating-point coordinates,
+    traditionally called x, y, and z.
 
     The QVector3D class can also be used to represent vertices in 3D space.
     We therefore do not need to provide a separate vertex class.
@@ -529,6 +541,7 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
     \fn QVector3D::QVector3D(float xpos, float ypos, float zpos)
 
     Constructs a vector with coordinates (\a xpos, \a ypos, \a zpos).
+    All parameters must be finite.
 */
 
 /*!
@@ -560,7 +573,7 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
     \fn QVector3D::QVector3D(QVector2D vector, float zpos)
 
     Constructs a 3D vector from the specified 2D \a vector. The z
-    coordinate is set to \a zpos.
+    coordinate is set to \a zpos, which must be finite.
 
     \sa toVector2D()
 */
@@ -613,7 +626,7 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
 /*!
     \fn void QVector3D::setX(float x)
 
-    Sets the x coordinate of this point to the given \a x coordinate.
+    Sets the x coordinate of this point to the given finite \a x coordinate.
 
     \sa x(), setY(), setZ()
 */
@@ -621,7 +634,7 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
 /*!
     \fn void QVector3D::setY(float y)
 
-    Sets the y coordinate of this point to the given \a y coordinate.
+    Sets the y coordinate of this point to the given finite \a y coordinate.
 
     \sa y(), setX(), setZ()
 */
@@ -629,7 +642,7 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
 /*!
     \fn void QVector3D::setZ(float z)
 
-    Sets the z coordinate of this point to the given \a z coordinate.
+    Sets the z coordinate of this point to the given finite \a z coordinate.
 
     \sa z(), setX(), setY()
 */
@@ -695,7 +708,7 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
 /*!
     \fn QVector3D &QVector3D::operator*=(float factor)
 
-    Multiplies this vector's coordinates by the given \a factor, and
+    Multiplies this vector's coordinates by the given finite \a factor and
     returns a reference to this vector.
 
     \sa operator/=()
@@ -717,8 +730,8 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
 /*!
     \fn QVector3D &QVector3D::operator/=(float divisor)
 
-    Divides this vector's coordinates by the given \a divisor, and
-    returns a reference to this vector.
+    Divides this vector's coordinates by the given \a divisor, and returns a
+    reference to this vector. The \a divisor must not be either zero or NaN.
 
     \sa operator*=()
 */
@@ -727,8 +740,10 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
     \fn QVector3D &QVector3D::operator/=(QVector3D vector)
     \since 5.5
 
-    Divides the components of this vector by the corresponding
-    components in \a vector.
+    Divides each component of this vector by the corresponding component in \a
+    vector and returns a reference to this vector.
+
+    The \a vector must have no component that is either zero or NaN.
 
     \sa operator*=()
 */
@@ -751,8 +766,8 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
 /*!
     \fn QVector3D QVector3D::normal(QVector3D v1, QVector3D v2)
 
-    Returns the normal vector of a plane defined by vectors \a v1 and \a v2,
-    normalized to be a unit vector.
+    Returns the unit normal vector of a plane spanned by vectors \a v1 and \a
+    v2, which must not be parallel to one another.
 
     Use crossProduct() to compute the cross-product of \a v1 and \a v2 if you
     do not need the result to be normalized to a unit vector.
@@ -763,8 +778,8 @@ QDataStream &operator>>(QDataStream &stream, QVector2D &vector)
 /*!
     \fn QVector3D QVector3D::normal(QVector3D v1, QVector3D v2, QVector3D v3)
 
-    Returns the normal vector of a plane defined by vectors
-    \a v2 - \a v1 and \a v3 - \a v1, normalized to be a unit vector.
+    Returns the unit normal vector of a plane spanned by vectors \a v2 - \a v1
+    and \a v3 - \a v1, which must not be parallel to one another.
 
     Use crossProduct() to compute the cross-product of \a v2 - \a v1 and
     \a v3 - \a v1 if you do not need the result to be normalized to a
@@ -922,7 +937,7 @@ QVector3D QVector3D::unproject(const QMatrix4x4 &modelView, const QMatrix4x4 &pr
 /*! //! friend
     \fn const QVector3D QVector3D::operator*(float factor, QVector3D vector)
 
-    Returns a copy of the given \a vector,  multiplied by the given \a factor.
+    Returns a copy of the given \a vector, multiplied by the given finite \a factor.
 
     \sa QVector3D::operator*=()
 */
@@ -930,7 +945,7 @@ QVector3D QVector3D::unproject(const QMatrix4x4 &modelView, const QMatrix4x4 &pr
 /*! //! friend
     \fn const QVector3D QVector3D::operator*(QVector3D vector, float factor)
 
-    Returns a copy of the given \a vector,  multiplied by the given \a factor.
+    Returns a copy of the given \a vector, multiplied by the given finite \a factor.
 
     \sa QVector3D::operator*=()
 */
@@ -958,8 +973,10 @@ QVector3D QVector3D::unproject(const QMatrix4x4 &modelView, const QMatrix4x4 &pr
 /*! //! friend
     \fn const QVector3D QVector3D::operator/(QVector3D vector, float divisor)
 
-    Returns the QVector3D object formed by dividing all three components of
-    the given \a vector by the given \a divisor.
+    Returns the QVector3D object formed by dividing each component of the given
+    \a vector by the given \a divisor.
+
+    The \a divisor must not be either zero or NaN.
 
     \sa QVector3D::operator/=()
 */
@@ -968,8 +985,10 @@ QVector3D QVector3D::unproject(const QMatrix4x4 &modelView, const QMatrix4x4 &pr
     \fn const QVector3D QVector3D::operator/(QVector3D vector, QVector3D divisor)
     \since 5.5
 
-    Returns the QVector3D object formed by dividing components of the given
-    \a vector by a respective components of the given \a divisor.
+    Returns the QVector3D object formed by dividing each component of the given
+    \a vector by the corresponding component of the given \a divisor.
+
+    The \a divisor must have no component that is either zero or NaN.
 
     \sa QVector3D::operator/=()
 */
@@ -1100,6 +1119,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
     stream >> x;
     stream >> y;
     stream >> z;
+    Q_ASSERT(qIsFinite(x) && qIsFinite(y) && qIsFinite(z));
     vector.setX(x);
     vector.setY(y);
     vector.setZ(z);
@@ -1121,6 +1141,10 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
     \ingroup painting-3D
     \inmodule QtGui
 
+    Vectors are one of the main building blocks of 4D affine representations of
+    3D space. They consist of four finite floating-point coordinates,
+    traditionally called x, y, z and w.
+
     The QVector4D class can also be used to represent vertices in 4D space.
     We therefore do not need to provide a separate vertex class.
 
@@ -1145,6 +1169,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
     \fn QVector4D::QVector4D(float xpos, float ypos, float zpos, float wpos)
 
     Constructs a vector with coordinates (\a xpos, \a ypos, \a zpos, \a wpos).
+    All parameters must be finite.
 */
 
 /*!
@@ -1176,7 +1201,8 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
     \fn QVector4D::QVector4D(QVector2D vector, float zpos, float wpos)
 
     Constructs a 4D vector from the specified 2D \a vector. The z
-    and w coordinates are set to \a zpos and \a wpos respectively.
+    and w coordinates are set to \a zpos and \a wpos respectively,
+    each of which must be finite.
 
     \sa toVector2D()
 */
@@ -1198,7 +1224,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
     \fn QVector4D::QVector4D(QVector3D vector, float wpos)
 
     Constructs a 4D vector from the specified 3D \a vector. The w
-    coordinate is set to \a wpos.
+    coordinate is set to \a wpos, which must be finite.
 
     \sa toVector3D()
 */
@@ -1247,7 +1273,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
 /*!
     \fn void QVector4D::setX(float x)
 
-    Sets the x coordinate of this point to the given \a x coordinate.
+    Sets the x coordinate of this point to the given finite \a x coordinate.
 
     \sa x(), setY(), setZ(), setW()
 */
@@ -1255,7 +1281,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
 /*!
     \fn void QVector4D::setY(float y)
 
-    Sets the y coordinate of this point to the given \a y coordinate.
+    Sets the y coordinate of this point to the given finite \a y coordinate.
 
     \sa y(), setX(), setZ(), setW()
 */
@@ -1263,7 +1289,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
 /*!
     \fn void QVector4D::setZ(float z)
 
-    Sets the z coordinate of this point to the given \a z coordinate.
+    Sets the z coordinate of this point to the given finite \a z coordinate.
 
     \sa z(), setX(), setY(), setW()
 */
@@ -1271,7 +1297,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
 /*!
     \fn void QVector4D::setW(float w)
 
-    Sets the w coordinate of this point to the given \a w coordinate.
+    Sets the w coordinate of this point to the given finite \a w coordinate.
 
     \sa w(), setX(), setY(), setZ()
 */
@@ -1355,7 +1381,7 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
 /*!
     \fn QVector4D &QVector4D::operator*=(float factor)
 
-    Multiplies this vector's coordinates by the given \a factor, and
+    Multiplies this vector's coordinates by the given finite \a factor, and
     returns a reference to this vector.
 
     \sa operator/=()
@@ -1371,8 +1397,8 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
 /*!
     \fn QVector4D &QVector4D::operator/=(float divisor)
 
-    Divides this vector's coordinates by the given \a divisor, and
-    returns a reference to this vector.
+    Divides this vector's coordinates by the given \a divisor, and returns a
+    reference to this vector. The \a divisor must not be either zero or NaN.
 
     \sa operator*=()
 */
@@ -1381,8 +1407,10 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
     \fn QVector4D &QVector4D::operator/=(QVector4D vector)
     \since 5.5
 
-    Divides the components of this vector by the corresponding
-    components in \a vector.
+    Divides each component of this vector by the corresponding component of \a
+    vector and returns a reference to this vector.
+
+    The \a vector must have no component that is either zero or NaN.
 
     \sa operator*=()
 */
@@ -1463,8 +1491,10 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
 /*! //! friend
     \fn const QVector4D QVector4D::operator/(QVector4D vector, float divisor)
 
-    Returns the QVector4D object formed by dividing all four components of
-    the given \a vector by the given \a divisor.
+    Returns the QVector4D object formed by dividing each component of the given
+    \a vector by the given \a divisor.
+
+    The \a divisor must not be either zero or NaN.
 
     \sa QVector4D::operator/=()
 */
@@ -1473,8 +1503,10 @@ QDataStream &operator>>(QDataStream &stream, QVector3D &vector)
     \fn const QVector4D QVector4D::operator/(QVector4D vector, QVector4D divisor)
     \since 5.5
 
-    Returns the QVector4D object formed by dividing components of the given
-    \a vector by a respective components of the given \a divisor.
+    Returns the QVector4D object formed by dividing each component of the given
+    \a vector by the corresponding component of the given \a divisor.
+
+    The \a divisor must have no component that is either zero or NaN.
 
     \sa QVector4D::operator/=()
 */
@@ -1611,6 +1643,7 @@ QDataStream &operator>>(QDataStream &stream, QVector4D &vector)
     stream >> y;
     stream >> z;
     stream >> w;
+    Q_ASSERT(qIsFinite(x) && qIsFinite(y) && qIsFinite(z) && qIsFinite(w));
     vector.setX(x);
     vector.setY(y);
     vector.setZ(z);
diff --git a/src/gui/math3d/qvectornd.h b/src/gui/math3d/qvectornd.h
index 8d2789338c..153f3743d8 100644
--- a/src/gui/math3d/qvectornd.h
+++ b/src/gui/math3d/qvectornd.h
@@ -147,11 +147,14 @@ QT_WARNING_POP
 
     constexpr friend inline QVector2D operator/(QVector2D vector, float divisor)
     {
+        Q_ASSERT(divisor < 0 || divisor > 0);
         return QVector2D(vector.v[0] / divisor, vector.v[1] / divisor);
     }
 
     constexpr friend inline QVector2D operator/(QVector2D vector, QVector2D divisor)
     {
+        Q_ASSERT(divisor.v[0] < 0 || divisor.v[0] > 0);
+        Q_ASSERT(divisor.v[1] < 0 || divisor.v[1] > 0);
         return QVector2D(vector.v[0] / divisor.v[0], vector.v[1] / divisor.v[1]);
     }
 
@@ -288,12 +291,17 @@ QT_WARNING_POP
 
     constexpr friend inline QVector3D operator/(QVector3D vector, float divisor)
     {
+        Q_ASSERT(divisor < 0 || divisor > 0);
         return QVector3D(vector.v[0] / divisor, vector.v[1] / divisor, vector.v[2] / divisor);
     }
 
     constexpr friend inline QVector3D operator/(QVector3D vector, QVector3D divisor)
     {
-        return QVector3D(vector.v[0] / divisor.v[0], vector.v[1] / divisor.v[1], vector.v[2] / divisor.v[2]);
+        Q_ASSERT(divisor.v[0] > 0 || divisor.v[0] < 0);
+        Q_ASSERT(divisor.v[1] > 0 || divisor.v[1] < 0);
+        Q_ASSERT(divisor.v[2] > 0 || divisor.v[2] < 0);
+        return QVector3D(vector.v[0] / divisor.v[0], vector.v[1] / divisor.v[1],
+                         vector.v[2] / divisor.v[2]);
     }
 
     friend Q_GUI_EXPORT bool qFuzzyCompare(QVector3D v1, QVector3D v2) noexcept;
@@ -422,12 +430,18 @@ QT_WARNING_POP
 
     constexpr friend inline QVector4D operator/(QVector4D vector, float divisor)
     {
+        Q_ASSERT(divisor < 0 || divisor > 0);
         return QVector4D(vector.v[0] / divisor, vector.v[1] / divisor, vector.v[2] / divisor, vector.v[3] / divisor);
     }
 
     constexpr friend inline QVector4D operator/(QVector4D vector, QVector4D divisor)
     {
-        return QVector4D(vector.v[0] / divisor.v[0], vector.v[1] / divisor.v[1], vector.v[2] / divisor.v[2], vector.v[3] / divisor.v[3]);
+        Q_ASSERT(divisor.v[0] > 0 || divisor.v[0] < 0);
+        Q_ASSERT(divisor.v[1] > 0 || divisor.v[1] < 0);
+        Q_ASSERT(divisor.v[2] > 0 || divisor.v[2] < 0);
+        Q_ASSERT(divisor.v[3] > 0 || divisor.v[3] < 0);
+        return QVector4D(vector.v[0] / divisor.v[0], vector.v[1] / divisor.v[1],
+                         vector.v[2] / divisor.v[2], vector.v[3] / divisor.v[3]);
     }
 
     friend Q_GUI_EXPORT bool qFuzzyCompare(QVector4D v1, QVector4D v2) noexcept;
@@ -576,6 +590,7 @@ constexpr inline QVector2D &QVector2D::operator*=(QVector2D vector) noexcept
 
 constexpr inline QVector2D &QVector2D::operator/=(float divisor)
 {
+    Q_ASSERT(divisor < 0 || divisor > 0);
     v[0] /= divisor;
     v[1] /= divisor;
     return *this;
@@ -583,6 +598,8 @@ constexpr inline QVector2D &QVector2D::operator/=(float divisor)
 
 constexpr inline QVector2D &QVector2D::operator/=(QVector2D vector)
 {
+    Q_ASSERT(vector.v[0] > 0 || vector.v[0] < 0);
+    Q_ASSERT(vector.v[1] > 0 || vector.v[1] < 0);
     v[0] /= vector.v[0];
     v[1] /= vector.v[1];
     return *this;
@@ -736,6 +753,7 @@ constexpr inline QVector3D &QVector3D::operator*=(QVector3D vector) noexcept
 
 constexpr inline QVector3D &QVector3D::operator/=(float divisor)
 {
+    Q_ASSERT(divisor < 0 || divisor > 0);
     v[0] /= divisor;
     v[1] /= divisor;
     v[2] /= divisor;
@@ -744,6 +762,9 @@ constexpr inline QVector3D &QVector3D::operator/=(float divisor)
 
 constexpr inline QVector3D &QVector3D::operator/=(QVector3D vector)
 {
+    Q_ASSERT(vector.v[0] > 0 || vector.v[0] < 0);
+    Q_ASSERT(vector.v[1] > 0 || vector.v[1] < 0);
+    Q_ASSERT(vector.v[2] > 0 || vector.v[2] < 0);
     v[0] /= vector.v[0];
     v[1] /= vector.v[1];
     v[2] /= vector.v[2];
@@ -947,6 +968,7 @@ constexpr inline QVector4D &QVector4D::operator*=(QVector4D vector) noexcept
 
 constexpr inline QVector4D &QVector4D::operator/=(float divisor)
 {
+    Q_ASSERT(divisor < 0 || divisor > 0);
     v[0] /= divisor;
     v[1] /= divisor;
     v[2] /= divisor;
@@ -956,6 +978,10 @@ constexpr inline QVector4D &QVector4D::operator/=(float divisor)
 
 constexpr inline QVector4D &QVector4D::operator/=(QVector4D vector)
 {
+    Q_ASSERT(vector.v[0] > 0 || vector.v[0] < 0);
+    Q_ASSERT(vector.v[1] > 0 || vector.v[1] < 0);
+    Q_ASSERT(vector.v[2] > 0 || vector.v[2] < 0);
+    Q_ASSERT(vector.v[3] > 0 || vector.v[3] < 0);
     v[0] /= vector.v[0];
     v[1] /= vector.v[1];
     v[2] /= vector.v[2];