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Address review comments

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This commit is contained in:
Riccardo Gerosa 2022-10-20 15:28:29 -07:00
parent ed4d75a075
commit 82879ec19d
1 changed files with 4 additions and 10 deletions
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14
src/math/big/int.go
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@ -205,14 +205,14 @@ func (z *Int) MulRange(a, b int64) *Int {
return z
}
// Binomial sets z to the binomial coefficient of (n, k) and returns z.
// Binomial sets z to the binomial coefficient C(n, k) and returns z.
func (z *Int) Binomial(n_, k_ int64) *Int {
if k_ > n_ {
return z.SetInt64(0)
}
// reduce the number of multiplications by reducing k
if k_ > n_-k_ {
k_ = n_ - k_ // Binomial(n, k) == Binomial(n, n-k)
k_ = n_ - k_ // C(n, k) == C(n, n-k)
}
// C(n, k) == n * (n-1) * ... * (n-k+1) / k * (k-1) * ... * 1
// == n * (n-1) * ... * (n-k+1) / 1 * (1+1) * ... * k
@ -230,10 +230,7 @@ func (z *Int) Binomial(n_, k_ int64) *Int {
//
// z = 1
// i := 0
// for {
// if i == k {
// break
// }
// for i < k {
// z *= n-i
// i++
// z /= i
@ -242,10 +239,7 @@ func (z *Int) Binomial(n_, k_ int64) *Int {
n.SetInt64(n_)
k.SetInt64(k_)
z.Set(intOne)
for {
if i.Cmp(&k) == 0 {
break
}
for i.Cmp(&k) < 0 {
d.Sub(&n, &i)
z.Mul(z, &d)
i.Add(&i, intOne)