big: added a few missing functions:

- sign to determine if a value is < 0, == 0, > 0
- abs to compute absolute value
- Rat.IsInt to test if a rational number is representable as an integer

R=rsc
CC=golang-dev
https://golang.org/cl/1761042

src/pkg/big/int.go

@@ -20,6 +20,23 @@ type Int struct {
 var intOne = &Int{false, natOne}
 
 
+// Sign returns:
+//
+//	-1 if x <  0
+//	 0 if x == 0
+//	+1 if x >  0
+//
+func (x *Int) Sign() int {
+	if len(x.abs) == 0 {
+		return 0
+	}
+	if x.neg {
+		return -1
+	}
+	return 1
+}
+
+
 // SetInt64 sets z to x and returns z.
 func (z *Int) SetInt64(x int64) *Int {
 	neg := false
@@ -47,6 +64,14 @@ func (z *Int) Set(x *Int) *Int {
 }
 
 
+// Abs sets z to |x| (the absolute value of x) and returns z.
+func (z *Int) Abs(x *Int) *Int {
+	z.abs = z.abs.set(x.abs)
+	z.neg = false
+	return z
+}
+
+
 // Neg sets z to -x and returns z.
 func (z *Int) Neg(x *Int) *Int {
 	z.abs = z.abs.set(x.abs)

src/pkg/big/int_test.go

@@ -47,6 +47,18 @@ var prodZZ = []argZZ{
 }
 
 
+func TestSignZ(t *testing.T) {
+	var zero Int
+	for _, a := range sumZZ {
+		s := a.z.Sign()
+		e := a.z.Cmp(&zero)
+		if s != e {
+			t.Errorf("got %d; want %d for z = %v", s, e, a.z)
+		}
+	}
+}
+
+
 func TestSetZ(t *testing.T) {
 	for _, a := range sumZZ {
 		var z Int
@@ -61,6 +73,23 @@ func TestSetZ(t *testing.T) {
 }
 
 
+func TestAbsZ(t *testing.T) {
+	var zero Int
+	for _, a := range sumZZ {
+		var z Int
+		z.Abs(a.z)
+		var e Int
+		e.Set(a.z)
+		if e.Cmp(&zero) < 0 {
+			e.Sub(&zero, &e)
+		}
+		if z.Cmp(&e) != 0 {
+			t.Errorf("got z = %v; want %v", z, e)
+		}
+	}
+}
+
+
 func testFunZZ(t *testing.T, msg string, f funZZ, a argZZ) {
 	var z Int
 	f(&z, a.x, a.y)

src/pkg/big/rat.go

@@ -60,6 +60,23 @@ func (z *Rat) SetInt64(x int64) *Rat {
 }
 
 
+// Sign returns:
+//
+//	-1 if x <  0
+//	 0 if x == 0
+//	+1 if x >  0
+//
+func (x *Rat) Sign() int {
+	return x.a.Sign()
+}
+
+
+// IsInt returns true if the denominator of x is 1.
+func (x *Rat) IsInt() bool {
+	return len(x.b) == 1 && x.b[0] == 1
+}
+
+
 // Num returns the numerator of z; it may be <= 0.
 // The result is a reference to z's numerator; it
 // may change if a new value is assigned to z.
@@ -126,6 +143,14 @@ func (x *Rat) Cmp(y *Rat) (r int) {
 }
 
 
+// Abs sets z to |x| (the absolute value of x) and returns z.
+func (z *Rat) Abs(x *Rat) *Rat {
+	z.a.Abs(&x.a)
+	z.b = z.b.set(x.b)
+	return z
+}
+
+
 // Add sets z to the sum x+y and returns z.
 func (z *Rat) Add(x, y *Rat) *Rat {
 	a1 := mulNat(&x.a, y.b)

src/pkg/big/rat_test.go

@@ -84,6 +84,20 @@ func TestFloatString(t *testing.T) {
 }
 
 
+func TestRatSign(t *testing.T) {
+	zero := NewRat(0, 1)
+	for _, a := range setStringTests {
+		var x Rat
+		x.SetString(a.in)
+		s := x.Sign()
+		e := x.Cmp(zero)
+		if s != e {
+			t.Errorf("got %d; want %d for z = %v", s, e, &x)
+		}
+	}
+}
+
+
 type ratCmpTest struct {
 	rat1, rat2 string
 	out        int
@@ -114,6 +128,38 @@ func TestRatCmp(t *testing.T) {
 }
 
 
+func TestIsInt(t *testing.T) {
+	one := NewInt(1)
+	for _, a := range setStringTests {
+		var x Rat
+		x.SetString(a.in)
+		i := x.IsInt()
+		e := x.Denom().Cmp(one) == 0
+		if i != e {
+			t.Errorf("got %v; want %v for z = %v", i, e, &x)
+		}
+	}
+}
+
+
+func TestRatAbs(t *testing.T) {
+	zero := NewRat(0, 1)
+	for _, a := range setStringTests {
+		var z Rat
+		z.SetString(a.in)
+		var e Rat
+		e.Set(&z)
+		if e.Cmp(zero) < 0 {
+			e.Sub(zero, &e)
+		}
+		z.Abs(&z)
+		if z.Cmp(&e) != 0 {
+			t.Errorf("got z = %v; want %v", &z, &e)
+		}
+	}
+}
+
+
 type ratBinFun func(z, x, y *Rat) *Rat
 type ratBinArg struct {
 	x, y, z string