This example illustrates a problem with number shifting

[wollbit]

This example illustrates a problem with number shifting.

Code for testing:

// In the first example, a hexadecimal number is output binary as a string. However, this also works decimal!
let y = 0;
let x = 0x00000001; // Bit 1
console.log('1) ' + x.toString(2) );
// Result: 1) 1

// In the second example the 32nd bit is set to 1
x = 0x80000000; // Bit 32
console.log('2) ' + x.toString(2) );
// Result: 2) 10000000000000000000000000000000

// In the second example the 30nd bit is set to 1
x = 0x20000000; // Bit 30
console.log('3) ' + x.toString(2) );
// Result: 3) 100000000000000000000000000000

// In this example we shift the 30th bit one place to the left
x = 0x20000000; // Bit 30
y = x << 1;
console.log('4) ' + y.toString(2) );
// Result: 4) 1000000000000000000000000000000

// Up to here everything works normally

// The next example returns an unexpected value.
// Here the 30th bit is shifted two bits to the left to the position of the 32nd bit. The result is suddenly negative.
x = 0x20000000; // Bit 30
y = x << 2;
console.log('5) ' + y.toString(2) );
// Result: 5) -10000000000000000000000000000000

// This is how to get around the problem
x = 0x40000000; // Bit 31
x *= 2;
console.log('6) ' + x.toString(2) );
// Result: 6) 10000000000000000000000000000000