Documentation
floatingpoint arithmetics
 As described in previous recipes, the representation of the floatingpoint numbers also complicates the arithmetic. For general purposes, the operations on the builtin float64 are sufficient. In case more precision is needed, the math/big package comes into play. This recipe will show you how to handle this.
package main
import (
"fmt"
"math/big"
)
const (
PI = `3.1415926535897932384626433832795028841971693
993751058209749445923078164062862089986280348253
421170679821480865132823066470938446095505822317
253594081284811174502841027019385211055596446229
4895493038196`
diameter = 3.0
precision = 400
)
func main() {
pi, _ := new(big.Float).SetPrec(precision).SetString(PI)
d := new(big.Float).SetPrec(precision).SetFloat64(diameter)
circumference := new(big.Float).Mul(pi, d)
pi64, _ := pi.Float64()
fmt.Printf("Circumference big.Float = %.400f\n",
circumference)
fmt.Printf("Circumference float64 = %.400f\n", pi64*diameter)
sum := new(big.Float).Add(pi, pi)
fmt.Printf("Sum = %.400f\n", sum)
diff := new(big.Float).Sub(pi, pi)
fmt.Printf("Diff = %.400f\n", diff)
quo := new(big.Float).Quo(pi, pi)
fmt.Printf("Quocient = %.400f\n", quo)
}
output:
sangam:golangdaily sangam$ go run main.go
Circumference big.Float = 9.4247779607693797153879301498385086525915081981253174629248337769234492188586269958841044760263512039
Circumference float64 = 9.4247779607693793479938904056325554847717285156250000000000000000000000000000000000000000000000000000
Sum = 6.2831853071795864769252867665590057683943387987502116419498891846156328125724179972560696506842341360
Diff = 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Quocient = 1.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
How it works…

The big package provides support for the arithmetic of floatingpoint numbers with high precision. The previous example illustrates the basic operations over the numbers. Note that the code compares the operation with the float64 type and the big.Float type.

By working with numbers with a high precision, it is crucial to use the big.Float type. When big.Float is converted back to the builtin float64 type, high precision is lost.
The big package contains more operations of the Float type. See the documentation (https://golang.org/pkg/math/big/#Float) of this package for more details.