// run
// Copyright 2009 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.
// Test concurrency primitives: power series.
// Power series package
// A power series is a channel, along which flow rational
// coefficients. A denominator of zero signifies the end.
// Original code in Newsqueak by Doug McIlroy.
// See Squinting at Power Series by Doug McIlroy,
// https://swtch.com/~rsc/thread/squint.pdf
package main
import "os"
type rat struct {
num, den int64 // numerator, denominator
}
func (u rat) pr() {
if u.den == 1 {
print(u.num)
} else {
print(u.num, "/", u.den)
}
print(" ")
}
func (u rat) eq(c rat) bool {
return u.num == c.num && u.den == c.den
}
type dch struct {
req chan int
dat chan rat
nam int
}
type dch2 [2]*dch
var chnames string
var chnameserial int
var seqno int
func mkdch() *dch {
c := chnameserial % len(chnames)
chnameserial++
d := new(dch)
d.req = make(chan int)
d.dat = make(chan rat)
d.nam = c
return d
}
func mkdch2() *dch2 {
d2 := new(dch2)
d2[0] = mkdch()
d2[1] = mkdch()
return d2
}
// split reads a single demand channel and replicates its
// output onto two, which may be read at different rates.
// A process is created at first demand for a rat and dies
// after the rat has been sent to both outputs.
// When multiple generations of split exist, the newest
// will service requests on one channel, which is
// always renamed to be out[0]; the oldest will service
// requests on the other channel, out[1]. All generations but the
// newest hold queued data that has already been sent to
// out[0]. When data has finally been sent to out[1],
// a signal on the release-wait channel tells the next newer
// generation to begin servicing out[1].
func dosplit(in *dch, out *dch2, wait chan int) {
both := false // do not service both channels
select {
case <-out[0].req:
case <-wait:
both = true
select {
case <-out[0].req:
case <-out[1].req:
out[0], out[1] = out[1], out[0]
}
}
seqno++
in.req <- seqno
release := make(chan int)
go dosplit(in, out, release)
dat := <-in.dat
out[0].dat <- dat
if !both {
<-wait
}
<-out[1].req
out[1].dat <- dat
release <- 0
}
func split(in *dch, out *dch2) {
release := make(chan int)
go dosplit(in, out, release)
release <- 0
}
func put(dat rat, out *dch) {
<-out.req
out.dat <- dat
}
func get(in *dch) rat {
seqno++
in.req <- seqno
return <-in.dat
}
// Get one rat from each of n demand channels
func getn(in []*dch) []rat {
n := len(in)
if n != 2 {
panic("bad n in getn")
}
req := new([2]chan int)
dat := new([2]chan rat)
out := make([]rat, 2)
var i int
var it rat
for i = 0; i < n; i++ {
req[i] = in[i].req
dat[i] = nil
}
for n = 2 * n; n > 0; n-- {
seqno++
select {
case req[0] <- seqno:
dat[0] = in[0].dat
req[0] = nil
case req[1] <- seqno:
dat[1] = in[1].dat
req[1] = nil
case it = <-dat[0]:
out[0] = it
dat[0] = nil
case it = <-dat[1]:
out[1] = it
dat[1] = nil
}
}
return out
}
// Get one rat from each of 2 demand channels
func get2(in0 *dch, in1 *dch) []rat {
return getn([]*dch{in0, in1})
}
func copy(in *dch, out *dch) {
for {
<-out.req
out.dat <- get(in)
}
}
func repeat(dat rat, out *dch) {
for {
put(dat, out)
}
}
type PS *dch // power series
type PS2 *[2]PS // pair of power series
var Ones PS
var Twos PS
func mkPS() *dch {
return mkdch()
}
func mkPS2() *dch2 {
return mkdch2()
}
// Conventions
// Upper-case for power series.
// Lower-case for rationals.
// Input variables: U,V,...
// Output variables: ...,Y,Z
// Integer gcd; needed for rational arithmetic
func gcd(u, v int64) int64 {
if u < 0 {
return gcd(-u, v)
}
if u == 0 {
return v
}
return gcd(v%u, u)
}
// Make a rational from two ints and from one int
func i2tor(u, v int64) rat {
g := gcd(u, v)
var r rat
if v > 0 {
r.num = u / g
r.den = v / g
} else {
r.num = -u / g
r.den = -v / g
}
return r
}
func itor(u int64) rat {
return i2tor(u, 1)
}
var zero rat
var one rat
// End mark and end test
var finis rat
func end(u rat) int64 {
if u.den == 0 {
return 1
}
return 0
}
// Operations on rationals
func add(u, v rat) rat {
g := gcd(u.den, v.den)
return i2tor(u.num*(v.den/g)+v.num*(u.den/g), u.den*(v.den/g))
}
func mul(u, v rat) rat {
g1 := gcd(u.num, v.den)
g2 := gcd(u.den, v.num)
var r rat
r.num = (u.num / g1) * (v.num / g2)
r.den = (u.den / g2) * (v.den / g1)
return r
}
func neg(u rat) rat {
return i2tor(-u.num, u.den)
}
func sub(u, v rat) rat {
return add(u, neg(v))
}
func inv(u rat) rat { // invert a rat
if u.num == 0 {
panic("zero divide in inv")
}
return i2tor(u.den, u.num)
}
// print eval in floating point of PS at x=c to n terms
func evaln(c rat, U PS, n int) {
xn := float64(1)
x := float64(c.num) / float64(c.den)
val := float64(0)
for i := 0; i < n; i++ {
u := get(U)
if end(u) != 0 {
break
}
val = val + x*float64(u.num)/float64(u.den)
xn = xn * x
}
print(val, "\n")
}
// Print n terms of a power series
func printn(U PS, n int) {
done := false
for ; !done && n > 0; n-- {
u := get(U)
if end(u) != 0 {
done = true
} else {
u.pr()
}
}
print(("\n"))
}
// Evaluate n terms of power series U at x=c
func eval(c rat, U PS, n int) rat {
if n == 0 {
return zero
}
y := get(U)
if end(y) != 0 {
return zero
}
return add(y, mul(c, eval(c, U, n-1)))
}
// Power-series constructors return channels on which power
// series flow. They start an encapsulated generator that
// puts the terms of the series on the channel.
// Make a pair of power series identical to a given power series
func Split(U PS) *dch2 {
UU := mkdch2()
go split(U, UU)
return UU
}
// Add two power series
func Add(U, V PS) PS {
Z := mkPS()
go func() {
var uv []rat
for {
<-Z.req
uv = get2(U, V)
switch end(uv[0]) + 2*end(uv[1]) {
case 0:
Z.dat <- add(uv[0], uv[1])
case 1:
Z.dat <- uv[1]
copy(V, Z)
case 2:
Z.dat <- uv[0]
copy(U, Z)
case 3:
Z.dat <- finis
}
}
}()
return Z
}
// Multiply a power series by a constant
func Cmul(c rat, U PS) PS {
Z := mkPS()
go func() {
done := false
for !done {
<-Z.req
u := get(U)
if end(u) != 0 {
done = true
} else {
Z.dat <- mul(c, u)
}
}
Z.dat <- finis
}()
return Z
}
// Subtract
func Sub(U, V PS) PS {
return Add(U, Cmul(neg(one), V))
}
// Multiply a power series by the monomial x^n
func Monmul(U PS, n int) PS {
Z := mkPS()
go func() {
for ; n > 0; n-- {
put(zero, Z)
}
copy(U, Z)
}()
return Z
}
// Multiply by x
func Xmul(U PS) PS {
return Monmul(U, 1)
}
func Rep(c rat) PS {
Z := mkPS()
go repeat(c, Z)
return Z
}
// Monomial c*x^n
func Mon(c rat, n int) PS {
Z := mkPS()
go func() {
if c.num != 0 {
for ; n > 0; n = n - 1 {
put(zero, Z)
}
put(c, Z)
}
put(finis, Z)
}()
return Z
}
func Shift(c rat, U PS) PS {
Z := mkPS()
go func() {
put(c, Z)
copy(U, Z)
}()
return Z
}
// simple pole at 1: 1/(1-x) = 1 1 1 1 1 ...
// Convert array of coefficients, constant term first
// to a (finite) power series
/*
func Poly(a []rat) PS {
Z:=mkPS()
begin func(a []rat, Z PS) {
j:=0
done:=0
for j=len(a); !done&&j>0; j=j-1)
if(a[j-1].num!=0) done=1
i:=0
for(; i<j; i=i+1) put(a[i],Z)
put(finis,Z)
}()
return Z
}
*/
// Multiply. The algorithm is
// let U = u + x*UU
// let V = v + x*VV
// then UV = u*v + x*(u*VV+v*UU) + x*x*UU*VV
func Mul(U, V PS) PS {
Z := mkPS()
go func() {
<-Z.req
uv := get2(U, V)
if end(uv[0]) != 0 || end(uv[1]) != 0 {
Z.dat <- finis
} else {
Z.dat <- mul(uv[0], uv[1])
UU := Split(U)
VV := Split(V)
W := Add(Cmul(uv[0], VV[0]), Cmul(uv[1], UU[0]))
<-Z.req
Z.dat <- get(W)
copy(Add(W, Mul(UU[1], VV[1])), Z)
}
}()
return Z
}
// Differentiate
func Diff(U PS) PS {
Z := mkPS()
go func() {
<-Z.req
u := get(U)
if end(u) == 0 {
done := false
for i := 1; !done; i++ {
u = get(U)
if end(u) != 0 {
done = true
} else {
Z.dat <- mul(itor(int64(i)), u)
<-Z.req
}
}
}
Z.dat <- finis
}()
return Z
}
// Integrate, with const of integration
func Integ(c rat, U PS) PS {
Z := mkPS()
go func() {
put(c, Z)
done := false
for i := 1; !done; i++ {
<-Z.req
u := get(U)
if end(u) != 0 {
done = true
}
Z.dat <- mul(i2tor(1, int64(i)), u)
}
Z.dat <- finis
}()
return Z
}
// Binomial theorem (1+x)^c
func Binom(c rat) PS {
Z := mkPS()
go func() {
n := 1
t := itor(1)
for c.num != 0 {
put(t, Z)
t = mul(mul(t, c), i2tor(1, int64(n)))
c = sub(c, one)
n++
}
put(finis, Z)
}()
return Z
}
// Reciprocal of a power series
// let U = u + x*UU
// let Z = z + x*ZZ
// (u+x*UU)*(z+x*ZZ) = 1
// z = 1/u
// u*ZZ + z*UU +x*UU*ZZ = 0
// ZZ = -UU*(z+x*ZZ)/u
func Recip(U PS) PS {
Z := mkPS()
go func() {
ZZ := mkPS2()
<-Z.req
z := inv(get(U))
Z.dat <- z
split(Mul(Cmul(neg(z), U), Shift(z, ZZ[0])), ZZ)
copy(ZZ[1], Z)
}()
return Z
}
// Exponential of a power series with constant term 0
// (nonzero constant term would make nonrational coefficients)
// bug: the constant term is simply ignored
// Z = exp(U)
// DZ = Z*DU
// integrate to get Z
func Exp(U PS) PS {
ZZ := mkPS2()
split(Integ(one, Mul(ZZ[0], Diff(U))), ZZ)
return ZZ[1]
}
// Substitute V for x in U, where the leading term of V is zero
// let U = u + x*UU
// let V = v + x*VV
// then S(U,V) = u + VV*S(V,UU)
// bug: a nonzero constant term is ignored
func Subst(U, V PS) PS {
Z := mkPS()
go func() {
VV := Split(V)
<-Z.req
u := get(U)
Z.dat <- u
if end(u) == 0 {
if end(get(VV[0])) != 0 {
put(finis, Z)
} else {
copy(Mul(VV[0], Subst(U, VV[1])), Z)
}
}
}()
return Z
}
// Monomial Substition: U(c x^n)
// Each Ui is multiplied by c^i and followed by n-1 zeros
func MonSubst(U PS, c0 rat, n int) PS {
Z := mkPS()
go func() {
c := one
for {
<-Z.req
u := get(U)
Z.dat <- mul(u, c)
c = mul(c, c0)
if end(u) != 0 {
Z.dat <- finis
break
}
for i := 1; i < n; i++ {
<-Z.req
Z.dat <- zero
}
}
}()
return Z
}
func Init() {
chnameserial = -1
seqno = 0
chnames = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
zero = itor(0)
one = itor(1)
finis = i2tor(1, 0)
Ones = Rep(one)
Twos = Rep(itor(2))
}
func check(U PS, c rat, count int, str string) {
for i := 0; i < count; i++ {
r := get(U)
if !r.eq(c) {
print("got: ")
r.pr()
print("should get ")
c.pr()
print("\n")
panic(str)
}
}
}
const N = 10
func checka(U PS, a []rat, str string) {
for i := 0; i < N; i++ {
check(U, a[i], 1, str)
}
}
func main() {
Init()
if len(os.Args) > 1 { // print
print("Ones: ")
printn(Ones, 10)
print("Twos: ")
printn(Twos, 10)
print("Add: ")
printn(Add(Ones, Twos), 10)
print("Diff: ")
printn(Diff(Ones), 10)
print("Integ: ")
printn(Integ(zero, Ones), 10)
print("CMul: ")
printn(Cmul(neg(one), Ones), 10)
print("Sub: ")
printn(Sub(Ones, Twos), 10)
print("Mul: ")
printn(Mul(Ones, Ones), 10)
print("Exp: ")
printn(Exp(Ones), 15)
print("MonSubst: ")
printn(MonSubst(Ones, neg(one), 2), 10)
print("ATan: ")
printn(Integ(zero, MonSubst(Ones, neg(one), 2)), 10)
} else { // test
check(Ones, one, 5, "Ones")
check(Add(Ones, Ones), itor(2), 0, "Add Ones Ones") // 1 1 1 1 1
check(Add(Ones, Twos), itor(3), 0, "Add Ones Twos") // 3 3 3 3 3
a := make([]rat, N)
d := Diff(Ones)
for i := 0; i < N; i++ {
a[i] = itor(int64(i + 1))
}
checka(d, a, "Diff") // 1 2 3 4 5
in := Integ(zero, Ones)
a[0] = zero // integration constant
for i := 1; i < N; i++ {
a[i] = i2tor(1, int64(i))
}
checka(in, a, "Integ") // 0 1 1/2 1/3 1/4 1/5
check(Cmul(neg(one), Twos), itor(-2), 10, "CMul") // -1 -1 -1 -1 -1
check(Sub(Ones, Twos), itor(-1), 0, "Sub Ones Twos") // -1 -1 -1 -1 -1
m := Mul(Ones, Ones)
for i := 0; i < N; i++ {
a[i] = itor(int64(i + 1))
}
checka(m, a, "Mul") // 1 2 3 4 5
e := Exp(Ones)
a[0] = itor(1)
a[1] = itor(1)
a[2] = i2tor(3, 2)
a[3] = i2tor(13, 6)
a[4] = i2tor(73, 24)
a[5] = i2tor(167, 40)
a[6] = i2tor(4051, 720)
a[7] = i2tor(37633, 5040)
a[8] = i2tor(43817, 4480)
a[9] = i2tor(4596553, 362880)
checka(e, a, "Exp") // 1 1 3/2 13/6 73/24
at := Integ(zero, MonSubst(Ones, neg(one), 2))
for c, i := 1, 0; i < N; i++ {
if i%2 == 0 {
a[i] = zero
} else {
a[i] = i2tor(int64(c), int64(i))
c *= -1
}
}
checka(at, a, "ATan") // 0 -1 0 -1/3 0 -1/5
/*
t := Revert(Integ(zero, MonSubst(Ones, neg(one), 2)))
a[0] = zero
a[1] = itor(1)
a[2] = zero
a[3] = i2tor(1,3)
a[4] = zero
a[5] = i2tor(2,15)
a[6] = zero
a[7] = i2tor(17,315)
a[8] = zero
a[9] = i2tor(62,2835)
checka(t, a, "Tan") // 0 1 0 1/3 0 2/15
*/
}
}
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