x86-64大整数表示形式? [英] x86-64 Big Integer Representation?

问题描述

x86-64上的高性能高性能本机大整数库如何表示内存中的一个大整数? (或者是否有所不同?有最常用的方法吗?)

How do hig-performance native big-integer libraries on x86-64 represent a big integer in memory? (or does it vary? Is there a most common way?)

天真的我正在考虑将它们存储为以0终止的数字字符串，并以2为底的 ⁶⁴ .

Naively I was thinking about storing them as 0-terminated strings of numbers in base 2⁶⁴.

例如，假设X在内存中为:

For example suppose X is in memory as:

[8 bytes] Dn
.
.
[8 bytes] D2
[8 bytes] D1
[8 bytes] D0
[8 bytes] 0

让B = 2 ⁶⁴

然后

X = D _n * B ⁿ + ... + D ₂ * B ² + D ₁ * B ¹ + D ₀

X = D_n * Bⁿ + ... + D₂ * B² + D₁ * B¹ + D₀

空字符串(即8个字节的零)表示零.

The empty string (i.e. 8 bytes of zero) means zero.

这是一种合理的方法吗?这种方式的优缺点是什么?有更好的方法吗?

Is this a reasonable way? What are the pros and cons of this way? Is there a better way?

您将如何处理签名? 2的补码是否可以与此可变长度值一起使用?

How would you handle signedness? Does 2's complement work with this variable length value?

(发现: http://gmplib.org/manual/Integer-Internals.html 什么是肢体?)

(Found this: http://gmplib.org/manual/Integer-Internals.html Whats a limb?)

推荐答案

我认为这将是数组的最低值到最高值.我在汇编程序中实现了任意大小数字的加法. CPU提供了进位标志，使您可以轻松地执行这些类型的操作.您编写一个以字节大小的块执行操作的循环.进位标志包含在使用加进位加法"指令(ADC操作码)的下一个操作中.

I would think it would be as an array lowest value to highest. I implemented addition of arbitrary sized numbers in assembler. The CPU provides the carry flag that allows you to easily perform these sorts of operations. You write a loop that performs the operation in byte size chunks. The carry flag is included in the next operation using the "Add with carry" instruction (ADC opcode).

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