如何强制长双打用Cython的使用情况如何？ [英] How do I force usage of long doubles with Cython?
问题描述
我提前道歉为我的C知识贫乏：我使用Python code和写与用Cython使用标准的C函数几个模块以实现速度有很大提高。但是，我需要比 1e308 （是的，你没有看错）高的范围内，这是我目前使用的类型双复数获得和功能 cexp 和驾驶室。
I apologize in advance for my poor knowledge of C: I use Python to code and have written a few modules with Cython using the standard C functions to effect a great increase in speed. However, I need a range higher than 1e308 (yes, you read it right), which is what I currently get by using the type double complex and the functions cexp and cabs.
我想使用的功能 cexpl 和 cabsl ，并宣布我的变量是类型长双复，但 1e308后，我还是会遇到溢出。这可能意味着我的编译器长双打转换为双打，是这样吗？但根据维基百科，
I tried to use the functions cexpl and cabsl, and declared my variables to be of type long double complex, but I still encounter overflows after 1e308. This probably means that my compiler converts long doubles to doubles, is that right? But according to Wikipedia,
使用GNU C编译器，在x86处理器上长双80位扩展precision不管用什么类型（它可以是96位或128位）的物理存储的。[4]
With the GNU C Compiler, long double is 80-bit extended precision on x86 processors regardless of the physical storage used for the type (which can be either 96 or 128 bits)..[4]
我使用的是64位系统的Arch Linux（和Python 2.7.8，如果它事项）。
I am using a 64-bit system with arch Linux (and Python 2.7.8 if it matters).
我如何写强制使用长双打的用Cython模块？我需要这样大的数字，对一些科学计算我做的。
How do I write a Cython module that forces the use of long doubles? I need such big numbers for some scientific computation I am doing.
编辑：
旗-m128bit长双编译给出相同的结果。如图所示这里，
在X86-64编译器，-m128bit长双是默认的选择，因为它的ABI指定长双精度是16字节边界对齐。
In the x86-64 compiler, -m128bit-long-double is the default choice as its ABI specifies that long double is to be aligned on 16 byte boundary.
因此，这似乎没有什么区别。
So this seems to make no difference.
我也跑这下面的程序来检查我的系统上的范围：
I also ran this following program to check the range on my system:
#include <stdio.h>
#include <float.h>
int main()
{
printf("Storage size for float : %d \n", sizeof(float));
printf("Minimum float positive value: %E\n", FLT_MIN );
printf("Maximum float positive value: %E\n", FLT_MAX );
printf("Precision value: %d\n", FLT_DIG );
printf("Storage size for double : %d \n", sizeof(double));
printf("Minimum double positive value: %E\n", DBL_MIN );
printf("Maximum double positive value: %E\n", DBL_MAX );
printf("Precision value: %d\n", DBL_DIG );
printf("Storage size for long double : %d \n", sizeof(long double));
printf("Minimum long double positive value: %Le\n", LDBL_MIN );
printf("Maximum long double positive value: %Le\n", LDBL_MAX );
printf("Precision value: %d\n", LDBL_DIG );
return 0;
}
和得到了以下的输出：
Storage size for float : 4
Minimum float positive value: 1.175494E-38
Maximum float positive value: 3.402823E+38
Precision value: 6
Storage size for double : 8
Minimum double positive value: 2.225074E-308
Maximum double positive value: 1.797693E+308
Precision value: 15
Storage size for long double : 16
Minimum long double positive value: 3.362103e-4932
Maximum long double positive value: 1.189731e+4932
Precision value: 18
所以我想问题出在我的code，是这样吗？是否有任何明确的标识符我需要比声明变量，以确保我的程序实际上使用长双打添加其他的？
So I guess the problem lies in my code, is that right? Are there any explicit identifiers I need to add other than declaring variables to ensure that my program actually uses long doubles?
推荐答案
正如看到在编辑的问题，我的系统和行为通过打印正确的范围长双预期编译器，这里的相关变量是 LDBL_MAX = 1.189731e + 4932
As was seen in the edit to the question, my system and compiler was behaving as expected by printing the correct range for long double, the relevant variable here being LDBL_MAX = 1.189731e+4932
此外，与用Cython编写的模块提供正确类型的输出长双。
然而，由于这种类型本身并不在Python支持（请参见这问题），被返回的值大于最大尺寸双击， 1.797693E + 308 我的系统上更大因此被等同于 + INF + 0J 。因此，这是不相关的GCC所有，但到Python间preting双打长以不正确的方式。
Also, the module written with Cython was correctly giving an output of type long double.
However, since this type is not natively supported in Python (see this question), the value that was returned was greater than the maximum size of double ,1.797693E+308 on my system and hence being equated to +inf + 0j. So this was not related to gcc at all, but to Python interpreting long doubles in an incorrect way.
我也希望能解决这个问题通过与另一I2C模块，能够接受长双输入类型和过程进一步，从这个子部分预期的结果预计不会是一个浮动）。
I can hopefully get around this by working with another C module that can accept long double input types and process it further, the expected results from this sub-part is not expected to be outside the range of a double (or for that matter, even a float).
另一个选择可能是使用与Python库，可支持高precision和高范围内的数字，可能 GMPY
Another option might be to use libraries with Python that can support high precision and high range numbers, possibly GMPY.
这篇关于如何强制长双打用Cython的使用情况如何？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！
