内核函数CIRC_SPACE_TO_END
时间: 2023-09-16 16:12:37 浏览: 53
CIRC_SPACE_TO_END是一个宏函数,用于计算循环缓冲区中从当前位置到缓冲区末尾的可用空间大小。具体实现如下:
#define CIRC_SPACE_TO_END(head, tail, size) \
({ typeof(head) end = (head) + (size) - 1; \
(end - (tail)) & ((size)-1); })
其中,head表示缓冲区的头指针,tail表示当前位置的指针,size表示缓冲区的大小。首先,end指向缓冲区的末尾位置,即head + size - 1。然后,用end减去tail得到从当前位置到缓冲区末尾的距离,最后用(size-1)进行与运算,得到可用空间大小(因为缓冲区是循环的,所以需要用(size-1)进行与运算,以确保计算结果在0-size之间)。
相关问题
linux 5.10 CIRC_SPACE_TO_END
CIRC_SPACE_TO_END is a macro defined in the Linux kernel version 5.10 that calculates the number of bytes available from the current position in a circular buffer to the end of the buffer. The macro takes two parameters: the current position in the buffer (represented as a pointer), and the size of the buffer (represented as an integer). The macro uses the modulo operator to handle wrapping around the end of the buffer when calculating the available space.
Here is the definition of the CIRC_SPACE_TO_END macro in the Linux kernel version 5.10:
#define CIRC_SPACE_TO_END(head, tail, size) \
({ (head >= tail) ? (size - (head - tail)) : (tail - head - 1); })
The macro uses a ternary operator to check if the head of the buffer is greater than or equal to the tail. If so, it subtracts the head from the tail and subtracts the result from the size of the buffer to get the available space. If not, it subtracts the tail from the head and subtracts one (to account for the fact that there is one less byte available when the head is immediately before the tail) from the result to get the available space.
For example, suppose you have a circular buffer of size 10, with the head at index 8 and the tail at index 2. The CIRC_SPACE_TO_END macro would be called with the head pointer, tail pointer, and size of the buffer as arguments:
int head = 8;
int tail = 2;
int size = 10;
int space_to_end = CIRC_SPACE_TO_END(&head, &tail, size);
The macro would calculate that there are 4 bytes available from index 8 to the end of the buffer, and assign that value to the space_to_end variable.
circ_vmpdf如何使用
circ_vmpdf函数用于计算von Mises分布的概率密度函数值,其语法如下:
```
pdf = circ_vmpdf(theta, mu, kappa)
```
其中,`theta`是样本点的角度值,可以是一个向量;`mu`是分布的均值方向,是一个标量;`kappa`是分布的集中度参数,也是一个标量。
函数返回一个与`theta`同大小的向量`pdf`,其中每个元素表示对应角度值的概率密度函数值。
例如,如果我们想计算一个von Mises分布在角度0处的概率密度函数值,均值方向为30度,集中度参数为1,可以使用以下代码:
```
pdf = circ_vmpdf(0, 30, 1)
```
注意,`circ_vmpdf`函数的输入和输出都是以弧度为单位的角度值,如果需要使用角度值,可以使用`rad2deg`和`deg2rad`函数进行转换。