javascript number value adding, different result return in different adding style

Question

I am a newbie in javascript, one wired thing I meet is: the formula (z >>> 5 ^ y << 2) + (y >>> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z); result is -529764813, but if i store each sum part into a temp variable, then add them, the result is different -529691705. Please have a look at the variables used in the formula and the result mx, new_mx are different. The code is executed and watched in chrome JS console. Who can help me ?

>z
6
>y
13106
>sum
-1640531527
>k
[1685024337, 1683575095, 1110798964, 6387041]
>p
0
>e
2
>mx = (z >>> 5 ^ y << 2) + (y >>> 3 ^ z << 4) ^ (sum ^ y) + (k[p & 3 ^ e] ^ z);
-529764813
>t1  = (z >>> 5 ^ y << 2)
52424
>t2=(y >>> 3 ^ z << 4) ^ (sum ^ y) 
-1640543091
>t3=(k[p & 3 ^ e] ^ z)
1110798962
>new_mx=t1+t2+t3
-529691705

Residuum · Accepted Answer · 2012-05-26 14:21:28Z

2

Javascript only has float numbers, no integers. And bitwise operations in Javascript generally are not a good idea, see http://www.crockford.com/javascript/survey.html

For float arithmetic, see the classic What Every Computer Scientist Should Know About Floating-Point Arithmetic.

answered May 26, 2012 at 14:21

Residuum

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1 Comment

nhahtdh Over a year ago

+1. Didn't aware of this before. However, I still think the we can reliably use the bitwise operations, if the application absolutely needs it and the calculation involves only integer less than 53 bit precision (counting intermediary results).

nhahtdh · Accepted Answer · 2012-05-26 14:24:14Z

2

https://developer.mozilla.org/en/JavaScript/Reference/Operators/Operator_Precedence

+ has higher precedence than ^, so the formula is grouped like this:

((z >>> 5 ^ y << 2) + (y >>> 3 ^ z << 4)) ^ ((sum ^ y) + (k[p & 3 ^ e] ^ z))

answered May 26, 2012 at 14:24

nhahtdh

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1 Comment

Bear-Aaron Over a year ago

My godsh, I just realize that. JS is so different with other language operator priority. You helped me. Thank you so much.

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