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big: implemented Int.Binomial (to be used in test/hilbert.go with the

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forthcoming implementation of big.Rat)

R=rsc
CC=golang-dev
https://golang.org/cl/1229047
This commit is contained in:
Robert Griesemer 2010-05-20 23:10:51 -07:00
parent 709c5b2481
commit e3bfeec474
1 changed files with 18 additions and 9 deletions
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27
src/pkg/big/int.go
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@ -39,7 +39,7 @@ func NewInt(x int64) *Int {
}
// Set sets z to x.
// Set sets z to x and returns z.
func (z *Int) Set(x *Int) *Int {
z.abs = z.abs.set(x.abs)
z.neg = x.neg
@ -47,6 +47,14 @@ func (z *Int) Set(x *Int) *Int {
}
// Neg sets z to -x and returns z.
func (z *Int) Neg(x *Int) *Int {
z.abs = z.abs.set(x.abs)
z.neg = len(z.abs) > 0 && !x.neg // 0 has no sign
return z
}
// Add sets z to the sum x+y and returns z.
func (z *Int) Add(x, y *Int) *Int {
neg := x.neg
@ -127,6 +135,15 @@ func (z *Int) MulRange(a, b int64) *Int {
}
// Binomial sets z to the binomial coefficient of (n, k) and returns z.
func (z *Int) Binomial(n, k int64) *Int {
var a, b Int
a.MulRange(n-k+1, n)
b.MulRange(1, k)
return z.Quo(&a, &b)
}
// Quo sets z to the quotient x/y for y != 0 and returns z.
// If y == 0, a division-by-zero run-time panic occurs.
// See QuoRem for more details.
@ -237,14 +254,6 @@ func (z *Int) DivMod(x, y, m *Int) (*Int, *Int) {
}
// Neg computes the negation z = -x.
func (z *Int) Neg(x *Int) *Int {
z.abs = z.abs.set(x.abs)
z.neg = len(z.abs) > 0 && !x.neg // 0 has no sign
return z
}
// Cmp compares x and y and returns:
//
// -1 if x < y