浮点模操作 [英] Floating Point Modulo Operation

问题描述

我试图实现对三角函数的范围缩小操作。但是相反，我认为这可能是最好的传入数据只是执行模PI / 2的操作。我想知道有哪些算法和高效是此操作为32位IEEE 754浮点？

I am trying to implement the range reduction operation for trigonometry. But instead I think it might be better to just perform a modulo pi/2 operation on incoming data. I was wondering what algorithms exist and are efficient for this operation for 32-bit IEEE 754 floating-point?

我要实现这个组装，所以FMOD，除法，乘法等不只有一个指令提供给我。我处理器采用16位字，我已经实现了32位浮点加法，减法，乘法，除法，平方根，余弦和正弦。我只需要用于输入值正弦和余弦范围减少（模数）。

I have to implement this in assembly, so fmod, division, multiplication, etc. aren't available to me with just one instruction. My processor uses 16-bit words and I have implemented 32-bit floating point addition, subtraction, multiplication, division, square root, cosine, and sine. I just need range reduction (modulus) for inputting values to cosine and sine.

推荐答案

我认为标准库的 FMOD（）将在大多数情况下的最佳选择。这里有一个链接的几个简单的算法进行了讨论。

I think standard library's fmod() will be the best choice in most cases. Here's a link to a discussion of several simple algorithms.

在我的机器上， FMOD（）使用优化的内联汇编code（ /usr/include/bits/mathinline.h ）

On my machine, fmod() uses optimized inline assembly code (/usr/include/bits/mathinline.h):

#if defined __FAST_MATH__ && !__GNUC_PREREQ (3, 5)
__inline_mathcodeNP2 (fmod, __x, __y, \
  register long double __value;                           \
  __asm __volatile__                                  \
    ("1:    fprem\n\t"                            \
     "fnstsw    %%ax\n\t"                             \
     "sahf\n\t"                                   \
     "jp    1b"                               \
     : "=t" (__value) : "0" (__x), "u" (__y) : "ax", "cc");           \
  return __value)
#endif

所以它实际上使用专用的CPU指令（F $ P $点）进行计算。

So it actually uses a dedicated CPU instruction (fprem) for the calculation.

这篇关于浮点模操作的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！