code: func positiveScaleInt64(base int64, scale Scale) (int64, bool) {
  	switch scale {
  	case 0:
  		return base, true
  	case 1:
  		return int64MultiplyScale10(base)
  	case 2:
  		return int64MultiplyScale100(base)
  	case 3:
  		return int64MultiplyScale1000(base)
  	case 6:
  		return int64MultiplyScale(base, 1000000)
  	case 9:
  		return int64MultiplyScale(base, 1000000000)
  	default:
  		value := base
  		var ok bool
  		for i := Scale(0); i < scale; i++ {
  			if value, ok = int64MultiplyScale(value, 10); !ok {
  				return 0, false
  			}
  		}
  		return value, true
  	}
  }
docs: // positiveScaleInt64 multiplies base by 10^scale, returning false if the
  // value overflows. Passing a negative scale is undefined.