如何读取，使用R二进制文件64位二进制补码整数？ [英] How to read a 64-bit two's-complement integer from a binary file using R?

问题描述

据我了解，重新present R中一个64位整数，我需要使用双。这很好，但我需要从它被存储为大端64位二进制补码（长在Java）的二进制文件中读取这样的整数。

I gather that to represent a 64-bit integer in R I need to use a double. That's fine but I need to read such an integer from a binary file where it is stored as Big Endian 64-bit two's-complement (a java long).

我当然可以读出两个有符号整数4字节的块，像这样

I can of course read the two signed integers in 4 byte chunks like so

a = readBin(file, integer(), size=4, endian="big")
b = readBin(file, integer(), size=4, endian="big")

但我怎么结合他们在R以获得我所需要的双？

But how do I combine them in R to get the double I require?

推荐答案

这绝对是更好地阅读它作为比为双两个整数。 2的补64位的幅度小的负数再presentation，如-1，是楠的双，并对其做算术可能不会制定出你需要的方式。

It is definitely better to read it in as two integers than as a double. The 2's complement 64 bit representation of small magnitude negative numbers, such as -1, are NaN's in double, and doing arithmetic on them will probably not work out the way you need.

先取2的补问题了。我会认为 A 是较为显著的一半。如果它是负的，注意这一事实，并采取2的整数的补充。翻转所有位，然后添加一个来自矣 B 添加到 A 添加。

First take the 2's complement issue out. I am going to assume that a is the more significant half. If it is negative, note the fact and take the 2's complement of the integer. Flip all the bits, then add one with carry from the b add to the a add.

接下来，转换 A 翻一番，由2 ^ 32乘，并添加 B 。

Next, convert a to double, multiply by 2^32, and add b.

如果原始值是负的，否定的结果。

If the original value was negative, negate the result.

请注意，你可能无法得到确切的答案，如果原来的号码是太大了。

Note that you may not get the exact answer if the original number was too big.

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