CODEWITHSUNDEEP
python
jb.
jb.

Reputation: 10341

Convert pseudo code to Python

Just to be fully up front, this is regarding a homework, but this in itself is not the assignment. The assignment is using noise to create cool graphics. I have a bit of experience in Python but not enough to figure this simple thing out.

I'm having trouble generating a seeded-random [-1,1]. The pseudocode my teacher gave me is from Hugo Elias.

Pseudocode:

function Noise1(integer x, integer y)
    n = x + y * 57
    n = (n<<13) ^ n;
    return ( 1.0 - ( (n * (n * n * 15731 + 789221) + 1376312589) & 7fffffff) / 1073741824.0);    
  end function

My attempt in Python:

def noise(x, y):
    n = x + y * 57
    n = (n<<5) ^ n;
    return ( 1.0 - ( (n * (n * n * 15731 + 789221) + 1376312589) & 7fffffff) / 1073741824.0)

The problem is the & 7fffffff bit in return statement. First, I'm not sure what that operation is. Maybe a bit-shift? Second, I'm not sure how to do that operation in Python. I had just removed that part, but I am getting huge negative numbers, nowhere near a [-1,1]

Upvotes: 3

Views: 2782

Answers (3)

Karl Knechtel
Karl Knechtel

Reputation: 61498

The problem is the & 7fffffff bit in return statement. First, I'm not sure what that operation is. Maybe a bit-shift?

A bit mask. << is used for shifting. & is bitwise-AND. 7fffffff, interpreted as a hexadecimal number, is a quantity that, if re-written in binary, has 31 bits, all of which are 1. The effect is to select the low-order 31 bits of the value.

To tell Python that 7fffffff should be interpreted as a hexadecimal number, you must prefix it with 0x, hence 0x7fffffff.

Second, I'm not sure how to do that operation in Python.

The same way as in the pseudocode (i.e. with &).

Upvotes: 1

Serdalis
Serdalis

Reputation: 10489

The & symbol stands for bitwise AND
The ^ symbol stands for bitwise XOR

and the 7FFFFFFF is a HEX number.
In programming you can represent a hex number using 0x where 7FFFFFFF is 0x7FFFFFFF
Some further reading on hex numbers.

To do a binary AND in python you just use & 0x7FFFFFFF
see more here about bitwise operations in python

Upvotes: 3

varunl
varunl

Reputation: 20229

I replaced 7FFFFFFF with 0x7FFFFFFF in your existing code and tried plugging in some random values and all the answers which I got were in [-1, 1].

Upvotes: 1

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