The maximum value for float64 and complex128 type in Go

Question

i need to know the maximum value of float64 and complex128 variable types in golang. go doesn't seem to have an equivalent of float.h and i don't know how to calculate it.

Answer 1

For example,

package main

import (
    "fmt"
    "math"
)

func main() {
    const f = math.MaxFloat64
    fmt.Printf("%[1]T %[1]v\n", f)
    const c = complex(math.MaxFloat64, math.MaxFloat64)
    fmt.Printf("%[1]T %[1]v\n", c)
}

Output:

float64 1.7976931348623157e+308
complex128 (1.7976931348623157e+308+1.7976931348623157e+308i)

---

Package math

import "math" 

Floating-point limit values. Max is the largest finite value representable by the type. SmallestNonzero is the smallest positive, non-zero value representable by the type.

const (
        MaxFloat32             = 3.40282346638528859811704183484516925440e+38  // 2**127 * (2**24 - 1) / 2**23
        SmallestNonzeroFloat32 = 1.401298464324817070923729583289916131280e-45 // 1 / 2**(127 - 1 + 23)

        MaxFloat64             = 1.797693134862315708145274237317043567981e+308 // 2**1023 * (2**53 - 1) / 2**52
        SmallestNonzeroFloat64 = 4.940656458412465441765687928682213723651e-324 // 1 / 2**(1023 - 1 + 52)
)

---

The Go Programming Language Specification

Numeric types

A numeric type represents sets of integer or floating-point values. The predeclared architecture-independent numeric types are:

uint8       the set of all unsigned  8-bit integers (0 to 255)
uint16      the set of all unsigned 16-bit integers (0 to 65535)
uint32      the set of all unsigned 32-bit integers (0 to 4294967295)
uint64      the set of all unsigned 64-bit integers (0 to 18446744073709551615)

int8        the set of all signed  8-bit integers (-128 to 127)
int16       the set of all signed 16-bit integers (-32768 to 32767)
int32       the set of all signed 32-bit integers (-2147483648 to 2147483647)
int64       the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807)

float32     the set of all IEEE-754 32-bit floating-point numbers
float64     the set of all IEEE-754 64-bit floating-point numbers

complex64   the set of all complex numbers with float32 real and imaginary parts
complex128  the set of all complex numbers with float64 real and imaginary parts

byte        alias for uint8
rune        alias for int32

The value of an n-bit integer is n bits wide and represented using two's complement arithmetic.

There is also a set of predeclared numeric types with implementation-specific sizes:

uint     either 32 or 64 bits
int      same size as uint
uintptr  an unsigned integer large enough to store the uninterpreted bits of a pointer value

To avoid portability issues all numeric types are distinct except byte, which is an alias for uint8, and rune, which is an alias for int32. Conversions are required when different numeric types are mixed in an expression or assignment. For instance, int32 and int are not the same type even though they may have the same size on a particular architecture.

Answer 2

You can also consider using the Inf method from the math package which returns a value for infinity (positive or negative if you want), but is considered to be float64.

Not too sure if there is an argument for one or the other between math.MaxFloat64 and math.Inf(). Comparing the two I've found that Go interprets the infinity values to be larger than the max float ones.

package main

import (
    "fmt"
    "math"
)

func main() {
    infPos := math.Inf(1) // gives positive infinity
    fmt.Printf("%[1]T %[1]v\n", infPos)
    
    infNeg := math.Inf(-1) // gives negative infinity
    fmt.Printf("%[1]T %[1]v\n", infNeg)
}