blocks|key|2779232|text|为什么这些线不匹配？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2779233|Python：|2779234|++++val+-=+1+<<+bits|code-block|syntax|javascript|2779235|联署材料：|2779236|++++val+-=+(val+-+1)+<<+bits;|2779237|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Why do these lines not match?

Python:

<pre><code> val -= 1 &lt;&lt; bits
</code></pre>

JS:

<pre><code> val -= (val - 1) &lt;&lt; bits;
</code></pre>

blocks|key|424204|text|第一,|type|unstyled|depth|inlineStyleRanges|entityRanges|data|424205|val+-=+(val+-+1)+<<+bits;|code-block|syntax|javascript|424206|和|424207|val+-=+1+<<+bits|424208|是不对等的。|424209|由于二进制字符串有27位长，这很可能是问题的根源。|424210|更广泛地说，这两种语言对数字一词的定义非常不同。|424211|Python有任意精度整数。|offset|length|424212|长整数具有无限的精度。|blockquote|424213|相比之下，JavaScript有IEEE+64b化作整数的双倍和按位运算符将它们的操作数截断为32位。|424214|数字是64位浮点数，类似于Java的双重和双倍.没有整数类型。两个整数之间的除法可能会产生分数的结果。|424215|这意味着您最多可以存储在52位精度中，如果最高阶位大于2**52，那么低阶位将被截断。|424216|由于JavaScript的浮点特性，大二进制数中最不重要的位可能被舍入，而最重要的位可能被(<<)抛出。|style|CODE|424217|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/2.7/library/stdtypes.html#numeric-types-int-float-long-complex|1|http://www.crockford.com/javascript/survey.html|2|https://stackoverflow.com/questions/12125421/why-does-a-shift-by-0-truncate-the-decimal|3|http://en.wikipedia.org/wiki/IEEE_floating_point#Basic_formats^0|0|0|0|0|0|0|0|7|6|0|0|0|G|F|1|11|D|2|0|0|C|5|3|0|1A|2|0^^$0|@$1|2|3|4|5|6|7|1L|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1M|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1N|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|1O|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1P|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1R|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1S|8|@]|9|@$S|1T|T|1U|1|1V]]|A|$]]|$1|U|3|V|5|W|7|1W|8|@]|9|@]|A|$]]|$1|X|3|Y|5|6|7|1X|8|@]|9|@$S|1Y|T|1Z|1|20]|$S|21|T|22|1|23]]|A|$]]|$1|Z|3|10|5|W|7|24|8|@]|9|@]|A|$]]|$1|11|3|12|5|6|7|25|8|@]|9|@$S|26|T|27|1|28]]|A|$]]|$1|13|3|14|5|6|7|29|8|@$S|2A|T|2B|15|16]]|9|@]|A|$]]|$1|17|3|-4|5|6|7|2C|8|@]|9|@]|A|$]]]|18|$19|$5|1A|1B|1C|A|$1D|1E]]|1F|$5|1A|1B|1C|A|$1D|1G]]|1H|$5|1A|1B|1C|A|$1D|1I]]|1J|$5|1A|1B|1C|A|$1D|1K]]]]

First,

<pre><code>val -= (val - 1) &lt;&lt; bits;
</code></pre>

and

<pre><code>val -= 1 &lt;&lt; bits
</code></pre>

are not equivalent.

Since your binary string is 27 digits long, this is most likely the source of your problem.

<hr>

More generally, the two languages have very different definitions of the term number.

Python has <a href="https://docs.python.org/2.7/library/stdtypes.html#numeric-types-int-float-long-complex" rel="nofollow noreferrer">arbitrary precision integers</a>.

<blockquote>
 Long integers have unlimited precision.
</blockquote>

By contrast, JavaScript has <a href="http://www.crockford.com/javascript/survey.html" rel="nofollow noreferrer">IEEE 64b doubles pretending to be integers</a> and bitwise operators that <a href="https://stackoverflow.com/questions/12125421/why-does-a-shift-by-0-truncate-the-decimal">truncate their operands to 32 bits</a>.

<blockquote>
 Number is 64-bit floating point, similar to Java's double and Double. There is no integer type. Division between two integers may produce a fractional result.
</blockquote>

This means you can store at most <a href="http://en.wikipedia.org/wiki/IEEE_floating_point#Basic_formats" rel="nofollow noreferrer">52 bits of precision</a>, and if the highest order bit is greater than 2**52, then low order bits are truncated.

<hr>

Because of the floating point nature of JavaScript, the least significant bits of a large binary number might be rounded off, and the most significant bits might be thrown out by (<code>&lt;&lt;</code>).

In python 2.7, the following code returns the correct result (-18027917)

<pre><code>from __future__ import print_function

def twos_comp(val, bits):
 if (val &amp; (1 &lt;&lt; (bits - 1))) != 0:
 val -= 1 &lt;&lt; bits
 return val

valBinary = "110111011001110101001110011"
print(twos_comp(int(valBinary, 2), len(valBinary)))
</code></pre>

<hr>

In JavaScript (Node.js) the following code returns an incorrect result (1995238003)

<pre><code>function toTwosComplement(val, bits) {
 if ((val &amp; (1 &lt;&lt; (bits - 1))) != 0) {
 val -= (val - 1) &lt;&lt; bits;
 }
 return val;
}

valBinary = "110111011001110101001110011"; // same as python example
console.log(toTwosComplement(parseInt(valBinary, 2), valBinary.length));
</code></pre>

Evidently there is something different about the behaviour of the bit operators (or int / parseInt) but I haven't been able to see what it is.

Twos complement same code python / JavaScript different results

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在python2.7中，以下代码返回正确的结果(-18027917)from __future__ import print_functiondef twos_comp(val, bits): if (val & (1 << (bits - 1))) != 0: val -= 1 << bits ...

问两个补充相同代码python / JavaScript的不同结果
EN

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问两个补充相同代码python / JavaScript的不同结果EN