From e3bfeec4747fb1d44d4fa5da33fb5d37d5085f16 Mon Sep 17 00:00:00 2001 From: Robert Griesemer Date: Thu, 20 May 2010 23:10:51 -0700 Subject: [PATCH] big: implemented Int.Binomial (to be used in test/hilbert.go with the forthcoming implementation of big.Rat) R=rsc CC=golang-dev https://golang.org/cl/1229047 --- src/pkg/big/int.go | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-) diff --git a/src/pkg/big/int.go b/src/pkg/big/int.go index cdf5a7d554..e1e45858a5 100755 --- a/src/pkg/big/int.go +++ b/src/pkg/big/int.go @@ -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 -- 2.48.1