用C自定义数据类型 [英] custom data type in C

问题描述

我与加密工作，并需要使用一些真正大量涌现。我也使用carryless乘法需要它是由与发生在浮点数据作为其参数的函数加载它做m128i数据类型新的英特尔指令。

I am working with cryptography and need to use some really large numbers. I am also using the new Intel instruction for carryless multiplication that requires m128i data type which is done by loading it with a function that takes in floating point data as its arguments.

我需要存储2 ^ 1223整数，然后将其平方和存储价值。

I need to store 2^1223 integer and then square it and store that value as well.

我知道我可以使用GMP库，但我认为这将是更快地创建两个数据类型，这两个存储值如2 ^ 1224和2 ^ 2448。这将有较少overhead.I打算使用karatsuba乘以数字，所以我需要对数据类型进行唯一的操作就是另外我将打破数字向下，以适应m128i。

I know I can use the GMP library but I think it would be faster to create two data types that both store values like 2^1224 and 2^2448. It will have less overhead.I am going to using karatsuba to multiply the numbers so the only operation I need to perform on the data type is addition as I will be breaking the number down to fit m128i.

有人可以告诉我的方向朝着材料，可以帮助我创建整数的大小，我需要。

Can someone direct me in the direction towards material that can help me create the size of integer I need.

推荐答案

如果您需要自己的数据类型（无论它是数学等），你需要回落到结构和功能。例如：

If you need your own datatypes (regardless of whether it's for math, etc), you'll need to fall back to structures and functions. For example:

struct bignum_s {
    char bignum_data[1024];
}

的（很明显，你想找到正确的尺寸，这只是一个例子）的

大多数人最终typedefing它还有：

Most people end up typedefing it as well:

typedef struct bignum_s bignum;

然后创建一个需要两个（或其他）指针的数字功能，做你想做的：

And then create functions that take two (or whatever) pointers to the numbers to do what you want:

/* takes two bignums and ORs them together, putting the result back into a */
void
bignum_or(bignum *a, bignum *b) {
    int i;
    for(i = 0; i < sizeof(a->bignum_data); i++) {
        a->bignum_data[i] |= b->bignum_data[i];
    }
}

您真的要结束了界定近，你可能需要每一个功能，而这常常包括内存分配函数（ bignum_new ），内存释放函数（ bignum_free ）和init程序（ bignum_init ）。即使你不需要他们现在提前做将设置你为当code需要成长，后来发展。

You really want to end up defining nearly every function you might need, and this frequently includes memory allocation functions (bignum_new), memory freeing functions (bignum_free) and init routines (bignum_init). Even if you don't need them now, doing it in advance will set you up for when the code needs to grow and develop later.

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