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copied!<p>You can compare the assembly generated for basic functions (I used GCC 4.8.1 on OS X 10.7.4)</p> <pre><code>struct Point3D { float m_data[3]; }; struct Point3Ds { float x; float y; float z; }; double dot(const Point3D& p1, const Point3D& p2) { asm("# Dot - Point3D"); return p1.m_data[0] * p2.m_data[0] + p1.m_data[1] * p2.m_data[1] + p1.m_data[2] * p2.m_data[2]; } double dot(const Point3Ds& p1, const Point3Ds&p2) { asm("# Dot - Point3Ds"); return p1.x * p2.x + p1.y * p2.y + p1.z * p2.z; } Point3D cross(const Point3D& p1, const Point3D& p2) { asm("# Cross - Point3D"); return { p1.m_data[1] * p2.m_data[2] - p1.m_data[2] * p2.m_data[1], p1.m_data[2] * p2.m_data[0] - p1.m_data[0] * p2.m_data[2], p1.m_data[0] * p2.m_data[1] - p1.m_data[1] * p2.m_data[0]}; } Point3D cross(const Point3Ds& p1, const Point3Ds& p2) { asm("# Cross - Point3Ds"); return { p1.y * p2.z - p1.z * p2.y, p1.z * p2.x - p1.x * p2.z, p1.x * p2.y - p1.y * p2.x}; } </code></pre> <p>Compiling as <code>g++ -O3 -S</code> I obtain the following assembler (relevant parts):</p> <pre><code># 12 "point3f.cpp" 1 # Dot - Point3D # 0 "" 2 movss (%rdi), %xmm0 movss 4(%rdi), %xmm1 mulss (%rsi), %xmm0 mulss 4(%rsi), %xmm1 addss %xmm1, %xmm0 movss 8(%rdi), %xmm1 mulss 8(%rsi), %xmm1 addss %xmm1, %xmm0 unpcklps %xmm0, %xmm0 cvtps2pd %xmm0, %xmm0 ret LFE0: .align 4,0x90 .globl __Z3dotRK8Point3DsS1_ __Z3dotRK8Point3DsS1_: LFB1: # 19 "point3f.cpp" 1 # Dot - Point3Ds # 0 "" 2 movss (%rdi), %xmm0 movss 4(%rdi), %xmm1 mulss (%rsi), %xmm0 mulss 4(%rsi), %xmm1 addss %xmm1, %xmm0 movss 8(%rdi), %xmm1 mulss 8(%rsi), %xmm1 addss %xmm1, %xmm0 unpcklps %xmm0, %xmm0 cvtps2pd %xmm0, %xmm0 ret LFE1: .align 4,0x90 .globl __Z5crossRK7Point3DS1_ __Z5crossRK7Point3DS1_: LFB2: # 26 "point3f.cpp" 1 # Cross - Point3D # 0 "" 2 movss 4(%rdi), %xmm3 movss 8(%rdi), %xmm1 movss 8(%rsi), %xmm5 movaps %xmm3, %xmm2 movss 4(%rsi), %xmm4 movaps %xmm1, %xmm0 mulss %xmm5, %xmm2 mulss %xmm4, %xmm0 subss %xmm0, %xmm2 movss (%rdi), %xmm0 mulss %xmm0, %xmm5 movss %xmm2, -24(%rsp) movss (%rsi), %xmm2 mulss %xmm4, %xmm0 mulss %xmm2, %xmm1 mulss %xmm3, %xmm2 subss %xmm5, %xmm1 subss %xmm2, %xmm0 movss %xmm1, -20(%rsp) movss %xmm0, -16(%rsp) movq -24(%rsp), %xmm0 movd -16(%rsp), %xmm1 ret LFE2: .align 4,0x90 .globl __Z5crossRK8Point3DsS1_ __Z5crossRK8Point3DsS1_: LFB3: # 33 "point3f.cpp" 1 # Cross - Point3Ds # 0 "" 2 movss 4(%rdi), %xmm3 movss 8(%rdi), %xmm1 movss 8(%rsi), %xmm5 movaps %xmm3, %xmm2 movss 4(%rsi), %xmm4 movaps %xmm1, %xmm0 mulss %xmm5, %xmm2 mulss %xmm4, %xmm0 subss %xmm0, %xmm2 movss (%rdi), %xmm0 mulss %xmm0, %xmm5 movss %xmm2, -24(%rsp) movss (%rsi), %xmm2 mulss %xmm4, %xmm0 mulss %xmm2, %xmm1 mulss %xmm3, %xmm2 subss %xmm5, %xmm1 subss %xmm2, %xmm0 movss %xmm1, -20(%rsp) movss %xmm0, -16(%rsp) movq -24(%rsp), %xmm0 movd -16(%rsp), %xmm1 ret </code></pre> <p>So the assembly is identical. But I agree that it would be more practical to store as an static array (that is, a <code>float m_data[3]</code>) because I can have the best of both worlds: a single parameter to pass when I need to, and a high-level, idiomatic <code>x</code>, <code>y</code>, <code>z</code> via getters. In that sense, I believe I would implement such class in a manner similar to:</p> <pre><code>class MyPoint3S { public: MyPoint3S(float x, float y, float z) : m_data{x, y, z} { } // the following getters will be inlined float x() const { return m_data[0]; } float y() const { return m_data[1]; } float z() const { return m_data[2]; } // in case you want to use the pointer --- some would advice against // offering a hook to a private member. float* data() { return m_data; } private: float m_data[3]; }; </code></pre> <p>And use it like:</p> <pre><code>MyPoint3S p(1.0f, 2.0f, 3.0f); std::cout<<"p = "<<p.x()<<", "<<p.y()<<", "<<p.z()<<std::endl; </code></pre> <p>to obtain:</p> <pre><code>p = 1, 2, 3 </code></pre> <p>Or call OpenGL functions in whatever way you prefer:</p> <pre><code>glVertex3fv(p.data()); </code></pre> <p>or</p> <pre><code>glVertex3f(p.x(), p.y(), p.z()); </code></pre>

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