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// Package bigvector implements operations on vectors of immutable
// multi-precision integers.
package bigvector
import (
"math/big"
"github.com/mmcloughlin/addchain/internal/bigint"
)
// Vector of immutable multi-precision integers.
type Vector interface {
// Len returns vector length.
Len() int
// Idx returns integer at index i. Returned integer must not be written to.
Idx(i int) *big.Int
}
// New constructs an n-dimensional zero vector.
func New(n int) Vector {
return make(vector, n)
}
type vector []big.Int
func (v vector) Len() int { return len(v) }
func (v vector) Idx(i int) *big.Int { return &v[i] }
// NewBasis constructs an n-dimensional basis vector with a 1 in position i.
func NewBasis(n, i int) Vector {
return basis{n: n, i: i}
}
// Basis implementation saves allocations by returning pre-allocated zero and
// one integers based on the index requested.
var (
zero = bigint.Zero()
one = bigint.One()
)
type basis struct {
n int
i int
}
func (b basis) Len() int { return b.n }
func (b basis) Idx(i int) *big.Int {
switch {
case i >= b.n:
panic("bigvector: index out of range")
case i == b.i:
return one
default:
return zero
}
}
// Add vectors.
func Add(u, v Vector) Vector {
assertsamelen(u, v)
n := u.Len()
w := make(vector, n)
for i := 0; i < n; i++ {
w[i].Add(u.Idx(i), v.Idx(i))
}
return w
}
// Lsh left shifts every element of the vector v.
func Lsh(v Vector, s uint) Vector {
n := v.Len()
w := make(vector, n)
for i := 0; i < n; i++ {
w[i].Lsh(v.Idx(i), s)
}
return w
}
// assertsamelen panics if u and v are different lengths.
func assertsamelen(u, v Vector) {
if u.Len() != v.Len() {
panic("bigvector: length mismatch")
}
}
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