C++ C和x2B之间的差异+；应该相同的代码段

对于计算机图形学的家庭作业，我们必须编写一个函数，确定点

p

是否位于边

p1

到

p2

的左侧。现在，我的搭档和我有两个不同版本的函数，尽管计算的是同一个东西，但结果却不同

片段1:

// The direction of the line from p1 to p:
float lineX = p.x - p1.x;
float lineY = p.y - p1.y;
// The direction of the triangle's edge from p1 to p2:
float edgeX = p2.x - p1.x;
float edgeY = p2.y - p1.x;

// The z component of the cross product (line x edge):
float F = lineX * edgeY - lineY * edgeX;

float x = p.x;
float y = p.y;
float X = p1.x;
float Y = p1.y;
float dX = p2.x - p1.x;
float dY = p2.y - p1.y;

float F = ((x-X) * dY - (y-Y) * dX);

片段2:

// The direction of the line from p1 to p:
float lineX = p.x - p1.x;
float lineY = p.y - p1.y;
// The direction of the triangle's edge from p1 to p2:
float edgeX = p2.x - p1.x;
float edgeY = p2.y - p1.x;

// The z component of the cross product (line x edge):
float F = lineX * edgeY - lineY * edgeX;

float x = p.x;
float y = p.y;
float X = p1.x;
float Y = p1.y;
float dX = p2.x - p1.x;
float dY = p2.y - p1.y;

float F = ((x-X) * dY - (y-Y) * dX);

我知道浮点运算不是交换的，也不是结合的。然而，据我所知，计算顺序应该完全相同，因为

lineX=x-x

和

edgeX=dX

是否有一些编译器优化会干扰计算？

复制和粘贴错误：

float edgeX = p2.x - p1.x;
float edgeY = p2.y - p1.x;

（p1.x）？

复制和粘贴错误：

float edgeX = p2.x - p1.x;
float edgeY = p2.y - p1.x;

（p1.x）