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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements multi-precision rational numbers.
package big
import "strings"
// A Rat represents a quotient a/b of arbitrary precision. The zero value for
// a Rat, 0/0, is not a legal Rat.
type Rat struct {
a Int
b nat
}
// NewRat creates a new Rat with numerator a and denominator b.
func NewRat(a, b int64) *Rat {
return new(Rat).SetFrac64(a, b)
}
// SetFrac sets z to a/b and returns z.
func (z *Rat) SetFrac(a, b *Int) *Rat {
z.a.Set(a)
z.a.neg = a.neg != b.neg
z.b = z.b.set(b.abs)
return z.norm()
}
// SetFrac64 sets z to a/b and returns z.
func (z *Rat) SetFrac64(a, b int64) *Rat {
z.a.SetInt64(a)
if b < 0 {
z.b.setUint64(uint64(-b))
z.a.neg = !z.a.neg
return z.norm()
}
z.b = z.b.setUint64(uint64(b))
return z.norm()
}
// SetInt sets z to x (by making a copy of x) and returns z.
func (z *Rat) SetInt(x *Int) *Rat {
z.a.Set(x)
z.b = z.b.setWord(1)
return z
}
// SetInt64 sets z to x and returns z.
func (z *Rat) SetInt64(x int64) *Rat {
z.a.SetInt64(x)
z.b = z.b.setWord(1)
return z
}
// 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.
func (z *Rat) Num() *Int {
return &z.a
}
// Demom returns the denominator of z; it is always > 0.
// The result is a reference to z's denominator; it
// may change if a new value is assigned to z.
func (z *Rat) Denom() *Int {
return &Int{false, z.b}
}
func gcd(x, y nat) nat {
// Euclidean algorithm.
var a, b nat
a = a.set(x)
b = b.set(y)
for len(b) != 0 {
var q, r nat
_, r = q.div(r, a, b)
a = b
b = r
}
return a
}
func (z *Rat) norm() *Rat {
f := gcd(z.a.abs, z.b)
if len(z.a.abs) == 0 {
// z == 0
z.a.neg = false // normalize sign
z.b = z.b.setWord(1)
return z
}
if f.cmp(natOne) != 0 {
z.a.abs, _ = z.a.abs.div(nil, z.a.abs, f)
z.b, _ = z.b.div(nil, z.b, f)
}
return z
}
func mulNat(x *Int, y nat) *Int {
var z Int
z.abs = z.abs.mul(x.abs, y)
z.neg = len(z.abs) > 0 && x.neg
return &z
}
// Cmp compares x and y and returns:
//
// -1 if x < y
// 0 if x == y
// +1 if x > y
//
func (x *Rat) Cmp(y *Rat) (r int) {
return mulNat(&x.a, y.b).Cmp(mulNat(&y.a, x.b))
}
// 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)
a2 := mulNat(&y.a, x.b)
z.a.Add(a1, a2)
z.b = z.b.mul(x.b, y.b)
return z.norm()
}
// Sub sets z to the difference x-y and returns z.
func (z *Rat) Sub(x, y *Rat) *Rat {
a1 := mulNat(&x.a, y.b)
a2 := mulNat(&y.a, x.b)
z.a.Sub(a1, a2)
z.b = z.b.mul(x.b, y.b)
return z.norm()
}
// Mul sets z to the product x*y and returns z.
func (z *Rat) Mul(x, y *Rat) *Rat {
z.a.Mul(&x.a, &y.a)
z.b = z.b.mul(x.b, y.b)
return z.norm()
}
// Quo sets z to the quotient x/y and returns z.
// If y == 0, a division-by-zero run-time panic occurs.
func (z *Rat) Quo(x, y *Rat) *Rat {
if len(y.a.abs) == 0 {
panic("division by zero")
}
a := mulNat(&x.a, y.b)
b := mulNat(&y.a, x.b)
z.a.abs = a.abs
z.b = b.abs
z.a.neg = a.neg != b.neg
return z.norm()
}
// Neg sets z to -x (by making a copy of x if necessary) and returns z.
func (z *Rat) Neg(x *Rat) *Rat {
z.a.Neg(&x.a)
z.b = z.b.set(x.b)
return z
}
// Set sets z to x (by making a copy of x if necessary) and returns z.
func (z *Rat) Set(x *Rat) *Rat {
z.a.Set(&x.a)
z.b = z.b.set(x.b)
return z
}
// SetString sets z to the value of s and returns z and a boolean indicating
// success. s can be given as a fraction "a/b" or as a floating-point number
// optionally followed by an exponent. If the operation failed, the value of z
// is undefined.
func (z *Rat) SetString(s string) (*Rat, bool) {
if len(s) == 0 {
return z, false
}
// check for a quotient
sep := strings.Index(s, "/")
if sep >= 0 {
if _, ok := z.a.SetString(s[0:sep], 10); !ok {
return z, false
}
s = s[sep+1:]
var n int
if z.b, _, n = z.b.scan(s, 10); n != len(s) {
return z, false
}
return z.norm(), true
}
// check for a decimal point
sep = strings.Index(s, ".")
// check for an exponent
e := strings.IndexAny(s, "eE")
var exp Int
if e >= 0 {
if e < sep {
// The E must come after the decimal point.
return z, false
}
if _, ok := exp.SetString(s[e+1:], 10); !ok {
return z, false
}
s = s[0:e]
}
if sep >= 0 {
s = s[0:sep] + s[sep+1:]
exp.Sub(&exp, NewInt(int64(len(s)-sep)))
}
if _, ok := z.a.SetString(s, 10); !ok {
return z, false
}
powTen := nat{}.expNN(natTen, exp.abs, nil)
if exp.neg {
z.b = powTen
z.norm()
} else {
z.a.abs = z.a.abs.mul(z.a.abs, powTen)
z.b = z.b.setWord(1)
}
return z, true
}
// String returns a string representation of z in the form "a/b".
func (z *Rat) String() string {
s := z.a.String()
if len(z.b) == 1 && z.b[0] == 1 {
return s
}
return s + "/" + z.b.string(10)
}
// FloatString returns a string representation of z in decimal form with prec
// digits of precision after the decimal point and the last digit rounded.
func (z *Rat) FloatString(prec int) string {
q, r := nat{}.div(nat{}, z.a.abs, z.b)
s := ""
if z.a.neg {
s = "-"
}
s += q.string(10)
if len(z.b) == 1 && z.b[0] == 1 {
return s
}
p := nat{}.expNN(natTen, nat{Word(prec)}, nil)
r = r.mul(r, p)
r, r2 := r.div(nat{}, r, z.b)
// see if we need to round up
r2 = r2.mul(r2, natTwo)
if z.b.cmp(r2) <= 0 {
r = r.add(r, natOne)
}
rs := r.string(10)
leadingZeros := prec - len(rs)
s += "." + strings.Repeat("0", leadingZeros) + rs
s = strings.TrimRight(s, "0")
return s
}