Task: Test integerness




Go: package main

import (
	"fmt"
	"math"
	"math/big"
	"reflect"
	"strings"
	"unsafe"
)







func Float64IsInt(f float64) bool {
	_, frac := math.Modf(f)
	return frac == 0
}




func Float32IsInt(f float32) bool {
	return Float64IsInt(float64(f))
}

func Complex128IsInt(c complex128) bool {
	return imag(c) == 0 && Float64IsInt(real(c))
}

func Complex64IsInt(c complex64) bool {
	return imag(c) == 0 && Float64IsInt(float64(real(c)))
}







type hasIsInt interface {
	IsInt() bool
}

var bigIntT = reflect.TypeOf((*big.Int)(nil))

func IsInt(i interface{}) bool {
	if ci, ok := i.(hasIsInt); ok {
		
		return ci.IsInt()
	}
	switch v := reflect.ValueOf(i); v.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16,
		reflect.Int32, reflect.Int64,
		reflect.Uint, reflect.Uint8, reflect.Uint16,
		reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		
		return true
	case reflect.Float32, reflect.Float64:
		
		return Float64IsInt(v.Float())
	case reflect.Complex64, reflect.Complex128:
		
		return Complex128IsInt(v.Complex())
	case reflect.String:
		
		
		
		if r, ok := new(big.Rat).SetString(v.String()); ok {
			return r.IsInt()
		}
	case reflect.Ptr:
		
		if v.Type() == bigIntT {
			return true
		}
	}
	return false
}



type intbased int16
type complexbased complex64
type customIntegerType struct {
	
	
}

func (customIntegerType) IsInt() bool    { return true }
func (customIntegerType) String() string { return "<…>" }

func main() {
	hdr := fmt.Sprintf("%27s  %-6s %s\n", "Input", "IsInt", "Type")
	show2 := func(t bool, i interface{}, args ...interface{}) {
		istr := fmt.Sprint(i)
		fmt.Printf("%27s  %-6t %T ", istr, t, i)
		fmt.Println(args...)
	}
	show := func(i interface{}, args ...interface{}) {
		show2(IsInt(i), i, args...)
	}

	fmt.Print("Using Float64IsInt with float64:\n", hdr)
	neg1 := -1.
	for _, f := range []float64{
		0, neg1 * 0, -2, -2.000000000000001, 10. / 2, 22. / 3,
		math.Pi,
		math.MinInt64, math.MaxUint64,
		math.SmallestNonzeroFloat64, math.MaxFloat64,
		math.NaN(), math.Inf(1), math.Inf(-1),
	} {
		show2(Float64IsInt(f), f)
	}

	fmt.Print("\nUsing Complex128IsInt with complex128:\n", hdr)
	for _, c := range []complex128{
		3, 1i, 0i, 3.4,
	} {
		show2(Complex128IsInt(c), c)
	}

	fmt.Println("\nUsing reflection:")
	fmt.Print(hdr)
	show("hello")
	show(math.MaxFloat64)
	show("9e100")
	f := new(big.Float)
	show(f)
	f.SetString("1e-3000")
	show(f)
	show("(4+0i)", "(complex strings not parsed)")
	show(4 + 0i)
	show(rune('§'), "or rune")
	show(byte('A'), "or byte")
	var t1 intbased = 5200
	var t2a, t2b complexbased = 5 + 0i, 5 + 1i
	show(t1)
	show(t2a)
	show(t2b)
	x := uintptr(unsafe.Pointer(&t2b))
	show(x)
	show(math.MinInt32)
	show(uint64(math.MaxUint64))
	b, _ := new(big.Int).SetString(strings.Repeat("9", 25), 0)
	show(b)
	r := new(big.Rat)
	show(r)
	r.SetString("2/3")
	show(r)
	show(r.SetFrac(b, new(big.Int).SetInt64(9)))
	show("12345/5")
	show(new(customIntegerType))
}


Java: import java.math.BigDecimal;
import java.util.List;

public class TestIntegerness {
    private static boolean isLong(double d) {
        return isLong(d, 0.0);
    }

    private static boolean isLong(double d, double tolerance) {
        return (d - Math.floor(d)) <= tolerance || (Math.ceil(d) - d) <= tolerance;
    }

    @SuppressWarnings("ResultOfMethodCallIgnored")
    private static boolean isBigInteger(BigDecimal bd) {
        try {
            bd.toBigIntegerExact();
            return true;
        } catch (ArithmeticException ex) {
            return false;
        }
    }

    private static class Rational {
        long num;
        long denom;

        Rational(int num, int denom) {
            this.num = num;
            this.denom = denom;
        }

        boolean isLong() {
            return num % denom == 0;
        }

        @Override
        public String toString() {
            return String.format("%s/%s", num, denom);
        }
    }

    private static class Complex {
        double real;
        double imag;

        Complex(double real, double imag) {
            this.real = real;
            this.imag = imag;
        }

        boolean isLong() {
            return TestIntegerness.isLong(real) && imag == 0.0;
        }

        @Override
        public String toString() {
            if (imag >= 0.0) {
                return String.format("%s + %si", real, imag);
            }
            return String.format("%s - %si", real, imag);
        }
    }

    public static void main(String[] args) {
        List<Double> da = List.of(25.000000, 24.999999, 25.000100);
        for (Double d : da) {
            boolean exact = isLong(d);
            System.out.printf("%.6f is %s integer%n", d, exact ? "an" : "not an");
        }
        System.out.println();

        double tolerance = 0.00001;
        System.out.printf("With a tolerance of %.5f:%n", tolerance);
        for (Double d : da) {
            boolean fuzzy = isLong(d, tolerance);
            System.out.printf("%.6f is %s integer%n", d, fuzzy ? "an" : "not an");
        }
        System.out.println();

        List<Double> fa = List.of(-2.1e120, -5e-2, Double.NaN, Double.POSITIVE_INFINITY);
        for (Double f : fa) {
            boolean exact = !f.isNaN() && !f.isInfinite() && isBigInteger(new BigDecimal(f.toString()));
            System.out.printf("%s is %s integer%n", f, exact ? "an" : "not an");
        }
        System.out.println();

        List<Complex> ca = List.of(new Complex(5.0, 0.0), new Complex(5.0, -5.0));
        for (Complex c : ca) {
            boolean exact = c.isLong();
            System.out.printf("%s is %s integer%n", c, exact ? "an" : "not an");
        }
        System.out.println();

        List<Rational> ra = List.of(new Rational(24, 8), new Rational(-5, 1), new Rational(17, 2));
        for (Rational r : ra) {
            boolean exact = r.isLong();
            System.out.printf("%s is %s integer%n", r, exact ? "an" : "not an");
        }
    }
}