Why does dividing by zero for Float not raise an exception in Ruby?

Question

Dividing by zero for Integer raises a ZeroDivisionError:

0 / 0 # ZeroDivisionError

However dividing by zero for Float does not:

0.0 / 0   #NaN
0 / 0.0   #NaN
0.0 /0.0  #NaN    
1.0 / 0   #Infinity
1 / 0.0   #Infinity
1.0 /0.0  #Infinity

I was wondering why is there this difference in behaviour for Integer and Float in Ruby?

Answer 1

As with almost all programming languages, ruby's implementation of floating-point arithmetic is compliant to the IEEE 754 standard.

This specification (linked above) defines five exceptions that must (at least by default) be handled in a specific way:

• Invalid operation: mathematically undefined, e.g., the square root of a negative number. By default, returns qNaN.

• Division by zero: an operation on finite operands gives an exact infinite result, e.g., 1/0 or log(0). By default, returns ±infinity.

• Overflow: a result is too large to be represented correctly (i.e., its exponent with an unbounded exponent range would be larger than emax). By default, returns ±infinity for the round-to-nearest modes (and follows the rounding rules for the directed rounding modes).

• Underflow: a result is very small (outside the normal range) and is inexact. By default, returns a subnormal or zero (following the rounding rules).

• Inexact: the exact (i.e., unrounded) result is not representable exactly. By default, returns the correctly rounded result.

Therefore 1.0/0 must equal +Infinity, and 0.0/0 must equal NaN.

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Integer objects do not conform to the above standard. (There is no Infinity or NaN, and all operations are exact.) Therefore, it was a language-specific decision to raise an exception for operations such as 1/0.