2 Error-Free Options for Decimal handling in Golang

package main

import (
	"fmt"
	"log"

	"github.com/cockroachdb/apd/v2"
)

func main() {
	// Division needs a rounding specified.
	// Precision here is the total number of digits 
	// to the left and right of the decimal place.
	context := apd.BaseContext.WithPrecision(10)

	// x = 1.234
	xDecimal, _, err := apd.NewFromString("1.234")
	if err != nil {
		log.Fatalln(err)
	}

	// y = 3
	yDecimal := apd.New(3, 0)

	result := apd.New(0, 0)

	_, err = context.Quo(result, xDecimal, yDecimal)
	if err != nil {
		log.Fatalln(err)
	}

	fmt.Println(result)
}

package main

import (
	"errors"
	"fmt"
	"log"
	"math"

	"github.com/cockroachdb/apd/v2"
)

var (
	// DecimalCtx is the default context for decimal operations. Any change
	// in the exponent limits must still guarantee a safe conversion to the
	// postgres binary decimal format in the wire protocol, which uses an
	// int16. See pgwire/types.go.
	DecimalCtx = &apd.Context{
		Precision:   20,
		Rounding:    apd.RoundHalfUp,
		MaxExponent: 2000,
		MinExponent: -2000,
		// Don't error on invalid operation, return NaN instead.
		Traps: apd.DefaultTraps &^ apd.InvalidOperation,
	}
)

func main() {
	xDecimal, _, _ := apd.NewFromString("14.955")
	// Max 4 digits to the left and right of decimal place. Max 1 digit to right of decimal place.
	err := LimitDecimalWidth(xDecimal, 4, 1)
	if err != nil {
		log.Println(err)
	}
	fmt.Printf("x= %v\n", xDecimal)

	// Max 4 digits to the left and right of decimal place. Max 2 digits to right of decimal place.
	yDecimal, _, _ := apd.NewFromString("14.955")
	err = LimitDecimalWidth(yDecimal, 4, 2)
	if err != nil {
		log.Println(err)
	}
	fmt.Printf("y= %v\n", yDecimal)
}

func LimitDecimalWidth(d *apd.Decimal, precision, scale int) error {
	if d.Form != apd.Finite || precision <= 0 {
		return nil
	}
	// Use +1 here because it is inverted later.
	if scale < math.MinInt32+1 || scale > math.MaxInt32 {
		return errors.New("out of range")
	}
	if scale > precision {
		return fmt.Errorf("scale (%d) must be between 0 and precision (%d)", scale, precision)
	}

	// http://www.postgresql.org/docs/9.5/static/datatype-numeric.html
	// "If the scale of a value to be stored is greater than
	// the declared scale of the column, the system will round the
	// value to the specified number of fractional digits. Then,
	// if the number of digits to the left of the decimal point
	// exceeds the declared precision minus the declared scale, an
	// error is raised."

	c := DecimalCtx.WithPrecision(uint32(precision))
	c.Traps = apd.InvalidOperation

	if _, err := c.Quantize(d, d, -int32(scale)); err != nil {
		var lt string
		switch v := precision - scale; v {
		case 0:
			lt = "1"
		default:
			lt = fmt.Sprintf("10^%d", v)
		}
		return fmt.Errorf("value with precision %d, scale %d must round to an absolute value less than %s", precision, scale, lt)
	}
	return nil
}

Output

x= 15.0
y= 14.96

// PostgreSQL
SELECT ('1.234'::numeric/'3'::numeric)::numeric(20,10);

// CockroachDB
SELECT ('1.234'::decimal/'3'::decimal)::decimal(20,10);