Pre-defined floating point types

The following floating point types are pre-defined:

float

the generic floating point type; its size used to be platform dependent, but now it is always mapped to float64. This type should be used in general.

floatXX

an implementation may define additional floating point types of XX bits using this naming scheme (example: float64 is a 64 bit wide float). The current implementation supports float32 and float64. Literals of these types have the suffix ‘fXX.

Automatic type conversion in expressions with different kinds of floating point types is performed: See Convertible relation for further details. Arithmetic performed on floating point types follows the IEEE standard. Integer types are not converted to floating point types automatically and vice versa.

The IEEE standard defines five types of floating-point exceptions:

• Invalid: operations with mathematically invalid operands, for example 0.0/0.0, sqrt(-1.0), and log(-37.8).
• Division by zero: divisor is zero and dividend is a finite nonzero number, for example 1.0/0.0.
• Overflow: operation produces a result that exceeds the range of the exponent, for example MAXDOUBLE+0.0000000000001e308.
• Underflow: operation produces a result that is too small to be represented as a normal number, for example, MINDOUBLE * MINDOUBLE.
• Inexact: operation produces a result that cannot be represented with infinite precision, for example, 2.0 / 3.0, log(1.1) and 0.1 in input.

The IEEE exceptions are either ignored during execution or mapped to the Nim exceptions: FloatInvalidOpDefect, FloatDivByZeroDefect, FloatOverflowDefect, FloatUnderflowDefect, and FloatInexactDefect. These exceptions inherit from the FloatingPointDefect base class.

Nim provides the pragmas nanChecks and infChecks to control whether the IEEE exceptions are ignored or trap a Nim exception:

{.nanChecks: on, infChecks: on.}
var a = 1.0
var b = 0.0
echo b / b # raises FloatInvalidOpDefect
echo a / b # raises FloatOverflowDefect

In the current implementation FloatDivByZeroDefect and FloatInexactDefect are never raised. FloatOverflowDefect is raised instead of FloatDivByZeroDefect. There is also a floatChecks pragma that is a short-cut for the combination of nanChecks and infChecks pragmas. floatChecks are turned off as default.

The only operations that are affected by the floatChecks pragma are the +, -, *, / operators for floating point types.

An implementation should always use the maximum precision available to evaluate floating pointer values during semantic analysis; this means expressions like 0.09’f32 + 0.01’f32 == 0.09’f64 + 0.01’f64 that are evaluating during constant folding are true.