big number calculation

[SwapOperator]

Hi!
I would like to know how to calculate shift and bitwise for number like this:

I have tried:
let x = 6277101735386680764176071790128604881410404459395608870912
math.bitAnd(math.rightArithShift(x, 16), 2 ** 16 - 1)

the answer should be 30 but I got 0

[josdejong]

Please read the docs on how to use bignumbers. In your example you're creating a regular number x and not a BigNumber

[SwapOperator]

Please read the docs on how to use bignumbers. In your example you're creating a regular number x and not a BigNumber

sorry for this incorrect syntax, I tried so many options and I still don't have an answer.

import { create, all } from 'mathjs'

// create a mathjs instance with configuration
const config = {
  number: 'BigNumber'
}
const math = create(all, config)
//I receive hexadecimal so I convert it to the string (0x01000000000000000100000000000000640000001e001e0000)
let x = math.bignumber(6277101735386680764176071790128604881410404459395608870912);
console.log(math.bitAnd(math.rightArithShift(x, 16),65535)); // 0
console.log(math.bitAnd(math.rightArithShift(x, 16),(2 ** 16 - 1))); //0

I use python to check my math and it works fine, here I has stuck for 2 days already
for instance

print((6277101735386680764176071790128604881410404459395608870912 >> 16))

is not the same as

math.rightArithShift(x, 16)

thank you!

[SwapOperator]

Also, if I shift to 32 I should receive number 30 too, but got 50176

import { create, all } from 'mathjs'

// create a mathjs instance with configuration
const config = {
  number: 'BigNumber'
}
const math = create(all, config)
//I receive hexadecimal so I convert it to the string (0x01000000000000000100000000000000640000001e001e0000)
let x = math.bignumber(6277101735386680764176071790128604881410404459395608870912);
console.log(math.bitAnd(math.rightArithShift(x, 32),65535)); // 50176
console.log("100% log", math.bitAnd(math.rightArithShift(x, 32),65535)); // 50176

[SwapOperator]

and there is a full python example

print((6277101735386680764176071790128604881410404459395608870912 >> 16) & (2 ** 16 - 1)) #30
print((6277101735386680764176071790128604881410404459395608870912 >> 32) & (2 ** 16 - 1)) #30

[SwapOperator]

ok that was a bit difficult but I got the success:

import { create, all } from 'mathjs'

// create a mathjs instance with configuration
const config = {
  number: 'BigNumber'
}
const math = create(all, config)
let x = math.bignumber(6277101735386680764176071790128604881410404459395608870912);
let string1 = String(x.toString() +" >> 16 & 65535");
console.log("string1 ", string1)
console.log("result", math.evaluate(string1))

[josdejong]

Is it an idea to mark #2377 (comment) as answer, containing two complete examples? The code here still misses how to create x (which should be created as a BigNumber, not a number)

[SwapOperator]

I edited my answer. Also in your example I would change

const { create, all } = require('..')

to

import { create, all } from 'mathjs'

[josdejong]

👍 done

[SwapOperator]

So why this example doesn't work?

import { create, all } from 'mathjs'

// create a mathjs instance with configuration
const config = {
  number: 'BigNumber'
}
const math = create(all, config)
//I receive hexadecimal so I convert it to the string (0x01000000000000000100000000000000640000001e001e0000)
let x = math.bignumber(6277101735386680764176071790128604881410404459395608870912);
console.log(math.bitAnd(math.rightArithShift(x, 16),65535)); // 0
console.log(math.bitAnd(math.rightArithShift(x, 16),(2 ** 16 - 1))); //0

[josdejong]

So why this example doesn't work?

You're first creating a number, and then turning the number into a BigNumber. But by then you've already lost you're precision.

You can do

import { create, all } from 'mathjs'

const math = create(all)

let x = math.bignumber('6277101735386680764176071790128604881410404459395608870912')
let result = math.bitAnd(math.rightArithShift(x, 16), 2 ** 16 - 1)
console.log(result.toString()) // 30

or

import { create, all } from 'mathjs'

const math = create(all, { number: 'BigNumber'})

const result = math.evaluate('(6277101735386680764176071790128604881410404459395608870912 >> 16) & (2 ^ 16 - 1)')
console.log(result.toString()) // 30

or create a math.parser, or pass a scope with x to the evaluation, etc. etc

[SwapOperator]

thank you