问题描述
当阅读CUDA 5.0编程指南时，我偶然发现了一个名为漏斗转移的功能，它存在于3.5计算能力的设备，但不是3.0。它包含一个注释参见参考手册，但是当我在手册中搜索漏斗移位术语时，我没有找到任何东西。
When reading through CUDA 5.0 Programming Guide I stumbled on a feature called "Funnel shift" which is present in 3.5 compute-capable device, but not 3.0. It contains an annotation "see reference manual", but when I search for the "funnel shift" term in the manual, I don't find anything.
因为它，但只有在的第8章： / p>
I tried googling for it, but only found a mention on http://www.cudahandbook.com, in the chapter 8:
GK110添加了64-可以使用以下内在函数访问的位漏斗转换指令：
GK110 added a 64-bit "funnel shift" instruction that may be accessed with the following intrinsics:
__ funnelshift_lc（）：返回左漏斗移位的最重要的32位。
__funnelshift_lc(): returns most significant 32 bits of a left funnel shift.
__ funnelshift_rc（）：返回最小有效32位右侧漏斗移位。
__funnelshift_rc(): returns least significant 32 bits of a right funnel shift.
这些内在函数实现为内联设备
函数（使用内联PTX汇编器）在sm_35_intrinsics.h中。
These intrinsics are implemented as inline device functions (using inline PTX assembler) in sm_35_intrinsics.h.
...但它仍然不解释左漏斗
...but it still does not explain what the "left funnel shift" or "right funnel shift" is.
那么，它是什么，什么地方需要它呢？
So, what is it and where does one need it?
推荐答案
在CUDA的情况下，两个32位寄存器连接在一起成为一个64位值;该值向左或向右移动;
In the case of CUDA, two 32-bit registers are concatenated together into a 64-bit value; that value is shifted left or right; and the most significant (for a left shift) or least significant (for right shift) 32 bits are returned.
sm_35_intrinsics.h的内在函数如下：
unsigned int __funnelshift_lc(unsigned int lo, unsigned int hi, unsigned int shift);
unsigned int __funnelshift_rc(unsigned int lo, unsigned int hi, unsigned int shift);
Andy Glew对渠道转移做了很好的描述：
Andy Glew has a good description of funnel shift here: http://semipublic.comp-arch.net/wiki/Funnel_shift
Glew列举了快速错位memcpy作为漏斗移位的一个应用程序;并且如上面注释中的njuffa所述，如果两个输入词相同，它可以用于实现旋转。
Glew cites fast misaligned memcpy as one application for funnel shift; and as njuffa mentions in the comments above, it can be used to implement rotate if the two input words are the same.
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