Update README to reflect changes

README.md

@@ -23,10 +23,12 @@ _Gopher image by [Renee French][rf], licensed under [Creative Commons 4.0 Attrib
 
 Every release includes the following modifications:
 
-- Restored Windows 7 and Windows Server 2008 R2 support (reverted [693def1](https://github.com/golang/go/commit/693def151adff1af707d82d28f55dba81ceb08e1))
+- Switched back to RtlGenRandom from ProcessPrng, which breaks Win7/2008R2 (reverted [693def1](https://github.com/golang/go/commit/693def151adff1af707d82d28f55dba81ceb08e1))
 - Added back LoadLibraryA fallback to load system libraries (reverted [a17d959](https://github.com/golang/go/commit/a17d959debdb04cd550016a3501dd09d50cd62e7))
+- Added back sysSocket fallback for socket syscalls (reverted [7c1157f](https://github.com/golang/go/commit/7c1157f9544922e96945196b47b95664b1e39108))
+- Added back Windows 7 console handle workaround (reverted [48042aa](https://github.com/golang/go/commit/48042aa09c2f878c4faa576948b07fe625c4707a))
 - Restored deprecated `go get` behavior for use outside modules (reverted [de4d503](https://github.com/golang/go/commit/de4d50316fb5c6d1529aa5377dc93b26021ee843))
-- Includes all improvements and bug fixes from Go 1.23.1
+- Includes all improvements and bug fixes from the corresponding upstream Go release
 
 The Windows binary provided here also supports Windows 7 and Windows Server 2008 R2
 
@@ -38,7 +40,7 @@ Binary distributions are **available at the [release page](https://github.com/th
 
 #### Windows Installation
 
-1. Download the `go-legacy-win7-<version>.windows-<arch>.zip` file.
+1. Download the `go-legacy-win7-<version>.windows_<arch>.zip` file.
 2. Extract the ZIP to `C:\` (or any preferred location). This will create a `go-legacy-win7` folder.
 3. Add the following to your system environment variables:
    - Add `C:\go-legacy-win7\bin` (or your chosen path) to the system `PATH`.
@@ -49,15 +51,15 @@ Binary distributions are **available at the [release page](https://github.com/th
 
 #### macOS and Linux Installation
 
-1. Download the appropriate `go-legacy-win7-<version>.<os>-<arch>.tar.gz` file.
+1. Download the appropriate `go-legacy-win7-<version>.<os>_<arch>.tar.gz` file.
 
-   - For macOS: `go-legacy-win7-<version>.darwin-<arch>.tar.gz`
+   - For macOS: `go-legacy-win7-<version>.darwin_<arch>.tar.gz`
-   - For Linux: `go-legacy-win7-<version>.linux-<arch>.tar.gz`
+   - For Linux: `go-legacy-win7-<version>.linux_<arch>.tar.gz`
 
 2. Extract the archive to `/usr/local`:
 
    ```
-   sudo tar -C /usr/local -xzf go-legacy-win7-<version>.<os>-<arch>.tar.gz
+   sudo tar -C /usr/local -xzf go-legacy-win7-<version>.<os>_<arch>.tar.gz
    ```
 
 3. Add the following to your shell configuration file:

VERSION

@@ -1,2 +1,2 @@
-go1.23.1
+go1.23.2
-time 2024-08-29T20:56:24Z
+time 2024-09-28T01:34:15Z

src/cmd/compile/internal/escape/solve.go

@@ -318,9 +318,9 @@ func containsClosure(f, c *ir.Func) bool {
 		return false
 	}
 
-	// Closures within function Foo are named like "Foo.funcN..."
+	// Closures within function Foo are named like "Foo.funcN..." or "Foo-rangeN".
 	// TODO(mdempsky): Better way to recognize this.
 	fn := f.Sym().Name
 	cn := c.Sym().Name
-	return len(cn) > len(fn) && cn[:len(fn)] == fn && cn[len(fn)] == '.'
+	return len(cn) > len(fn) && cn[:len(fn)] == fn && (cn[len(fn)] == '.' || cn[len(fn)] == '-')
 }

src/net/hook_windows.go

@@ -13,6 +13,7 @@ var (
 	hostsFilePath = windows.GetSystemDirectory() + "/Drivers/etc/hosts"
 
 	// Placeholders for socket system calls.
+	socketFunc    func(int, int, int) (syscall.Handle, error)                                                 = syscall.Socket
 	wsaSocketFunc func(int32, int32, int32, *syscall.WSAProtocolInfo, uint32, uint32) (syscall.Handle, error) = windows.WSASocket
 	connectFunc   func(syscall.Handle, syscall.Sockaddr) error                                                = syscall.Connect
 	listenFunc    func(syscall.Handle, int) error                                                             = syscall.Listen

src/net/internal/socktest/main_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !js && !plan9 && !wasip1 && !windows
+//go:build !js && !plan9 && !wasip1
 
 package socktest_test
 

src/net/internal/socktest/main_windows_test.go

@@ -0,0 +1,22 @@
+// Copyright 2015 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.
+
+package socktest_test
+
+import "syscall"
+
+var (
+	socketFunc func(int, int, int) (syscall.Handle, error)
+	closeFunc  func(syscall.Handle) error
+)
+
+func installTestHooks() {
+	socketFunc = sw.Socket
+	closeFunc = sw.Closesocket
+}
+
+func uninstallTestHooks() {
+	socketFunc = syscall.Socket
+	closeFunc = syscall.Closesocket
+}

src/net/internal/socktest/sys_windows.go

@@ -9,6 +9,35 @@ import (
 	"syscall"
 )
 
+// Socket wraps syscall.Socket.
+func (sw *Switch) Socket(family, sotype, proto int) (s syscall.Handle, err error) {
+	sw.once.Do(sw.init)
+	so := &Status{Cookie: cookie(family, sotype, proto)}
+	sw.fmu.RLock()
+	f, _ := sw.fltab[FilterSocket]
+	sw.fmu.RUnlock()
+	af, err := f.apply(so)
+	if err != nil {
+		return syscall.InvalidHandle, err
+	}
+	s, so.Err = syscall.Socket(family, sotype, proto)
+	if err = af.apply(so); err != nil {
+		if so.Err == nil {
+			syscall.Closesocket(s)
+		}
+		return syscall.InvalidHandle, err
+	}
+	sw.smu.Lock()
+	defer sw.smu.Unlock()
+	if so.Err != nil {
+		sw.stats.getLocked(so.Cookie).OpenFailed++
+		return syscall.InvalidHandle, so.Err
+	}
+	nso := sw.addLocked(s, family, sotype, proto)
+	sw.stats.getLocked(nso.Cookie).Opened++
+	return s, nil
+}
+
 // WSASocket wraps [syscall.WSASocket].
 func (sw *Switch) WSASocket(family, sotype, proto int32, protinfo *syscall.WSAProtocolInfo, group uint32, flags uint32) (s syscall.Handle, err error) {
 	sw.once.Do(sw.init)

src/net/main_windows_test.go

@@ -8,6 +8,7 @@ import "internal/poll"
 
 var (
 	// Placeholders for saving original socket system calls.
+	origSocket      = socketFunc
 	origWSASocket   = wsaSocketFunc
 	origClosesocket = poll.CloseFunc
 	origConnect     = connectFunc
@@ -17,6 +18,7 @@ var (
 )
 
 func installTestHooks() {
+	socketFunc = sw.Socket
 	wsaSocketFunc = sw.WSASocket
 	poll.CloseFunc = sw.Closesocket
 	connectFunc = sw.Connect
@@ -26,6 +28,7 @@ func installTestHooks() {
 }
 
 func uninstallTestHooks() {
+	socketFunc = origSocket
 	wsaSocketFunc = origWSASocket
 	poll.CloseFunc = origClosesocket
 	connectFunc = origConnect

src/net/sock_windows.go

@@ -20,6 +20,20 @@ func maxListenerBacklog() int {
 func sysSocket(family, sotype, proto int) (syscall.Handle, error) {
 	s, err := wsaSocketFunc(int32(family), int32(sotype), int32(proto),
 		nil, 0, windows.WSA_FLAG_OVERLAPPED|windows.WSA_FLAG_NO_HANDLE_INHERIT)
+	if err == nil {
+		return s, nil
+	}
+	// WSA_FLAG_NO_HANDLE_INHERIT flag is not supported on some
+	// old versions of Windows, see
+	// https://msdn.microsoft.com/en-us/library/windows/desktop/ms742212(v=vs.85).aspx
+	// for details. Just use syscall.Socket, if windows.WSASocket failed.
+	// See ../syscall/exec_unix.go for description of ForkLock.
+	syscall.ForkLock.RLock()
+	s, err = socketFunc(family, sotype, proto)
+	if err == nil {
+		syscall.CloseOnExec(s)
+	}
+	syscall.ForkLock.RUnlock()
 	if err != nil {
 		return syscall.InvalidHandle, os.NewSyscallError("socket", err)
 	}

src/runtime/time.go

@@ -29,6 +29,36 @@ type timer struct {
 	astate atomic.Uint8 // atomic copy of state bits at last unlock
 	state  uint8        // state bits
 	isChan bool         // timer has a channel; immutable; can be read without lock
+
+	// isSending is used to handle races between running a
+	// channel timer and stopping or resetting the timer.
+	// It is used only for channel timers (t.isChan == true).
+	// The lowest zero bit is set when about to send a value on the channel,
+	// and cleared after sending the value.
+	// The stop/reset code uses this to detect whether it
+	// stopped the channel send.
+	//
+	// An isSending bit is set only when t.mu is held.
+	// An isSending bit is cleared only when t.sendLock is held.
+	// isSending is read only when both t.mu and t.sendLock are held.
+	//
+	// Setting and clearing Uint8 bits handles the case of
+	// a timer that is reset concurrently with unlockAndRun.
+	// If the reset timer runs immediately, we can wind up with
+	// concurrent calls to unlockAndRun for the same timer.
+	// Using matched bit set and clear in unlockAndRun
+	// ensures that the value doesn't get temporarily out of sync.
+	//
+	// We use a uint8 to keep the timer struct small.
+	// This means that we can only support up to 8 concurrent
+	// runs of a timer, where a concurrent run can only occur if
+	// we start a run, unlock the timer, the timer is reset to a new
+	// value (or the ticker fires again), it is ready to run,
+	// and it is actually run, all before the first run completes.
+	// Since completing a run is fast, even 2 concurrent timer runs are
+	// nearly impossible, so this should be safe in practice.
+	isSending atomic.Uint8
+
 	blocked uint32 // number of goroutines blocked on timer's channel
 
 	// Timer wakes up at when, and then at when+period, ... (period > 0 only)
@@ -431,6 +461,15 @@ func (t *timer) stop() bool {
 		// Stop any future sends with stale values.
 		// See timer.unlockAndRun.
 		t.seq++
+
+		// If there is currently a send in progress,
+		// incrementing seq is going to prevent that
+		// send from actually happening. That means
+		// that we should return true: the timer was
+		// stopped, even though t.when may be zero.
+		if t.isSending.Load() > 0 {
+			pending = true
+		}
 	}
 	t.unlock()
 	if !async && t.isChan {
@@ -525,6 +564,15 @@ func (t *timer) modify(when, period int64, f func(arg any, seq uintptr, delay in
 		// Stop any future sends with stale values.
 		// See timer.unlockAndRun.
 		t.seq++
+
+		// If there is currently a send in progress,
+		// incrementing seq is going to prevent that
+		// send from actually happening. That means
+		// that we should return true: the timer was
+		// stopped, even though t.when may be zero.
+		if t.isSending.Load() > 0 {
+			pending = true
+		}
 	}
 	t.unlock()
 	if !async && t.isChan {
@@ -1013,6 +1061,24 @@ func (t *timer) unlockAndRun(now int64) {
 		}
 		t.updateHeap()
 	}
+
+	async := debug.asynctimerchan.Load() != 0
+	var isSendingClear uint8
+	if !async && t.isChan {
+		// Tell Stop/Reset that we are sending a value.
+		// Set the lowest zero bit.
+		// We do this awkward step because atomic.Uint8
+		// doesn't support Add or CompareAndSwap.
+		// We only set bits with t locked.
+		v := t.isSending.Load()
+		i := sys.TrailingZeros8(^v)
+		if i == 8 {
+			throw("too many concurrent timer firings")
+		}
+		isSendingClear = 1 << i
+		t.isSending.Or(isSendingClear)
+	}
+
 	t.unlock()
 
 	if raceenabled {
@@ -1028,7 +1094,6 @@ func (t *timer) unlockAndRun(now int64) {
 		ts.unlock()
 	}
 
-	async := debug.asynctimerchan.Load() != 0
 	if !async && t.isChan {
 		// For a timer channel, we want to make sure that no stale sends
 		// happen after a t.stop or t.modify, but we cannot hold t.mu
@@ -1044,6 +1109,10 @@ func (t *timer) unlockAndRun(now int64) {
 		// and double-check that t.seq is still the seq value we saw above.
 		// If not, the timer has been updated and we should skip the send.
 		// We skip the send by reassigning f to a no-op function.
+		//
+		// The isSending field tells t.stop or t.modify that we have
+		// started to send the value. That lets them correctly return
+		// true meaning that no value was sent.
 		lock(&t.sendLock)
 		if t.seq != seq {
 			f = func(any, uintptr, int64) {}
@@ -1053,6 +1122,9 @@ func (t *timer) unlockAndRun(now int64) {
 	f(arg, seq, delay)
 
 	if !async && t.isChan {
+		// We are no longer sending a value.
+		t.isSending.And(^isSendingClear)
+
 		unlock(&t.sendLock)
 	}
 

src/syscall/exec_windows.go

@@ -14,7 +14,6 @@ import (
 	"unsafe"
 )
 
-// ForkLock is not used on Windows.
 var ForkLock sync.RWMutex
 
 // EscapeArg rewrites command line argument s as prescribed
@@ -317,6 +316,18 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
 		}
 	}
 
+	info := _OSVERSIONINFOW{}
+	info.osVersionInfoSize = uint32(unsafe.Sizeof(info))
+	rtlGetVersion(&info)
+	isWin7 := info.majorVersion < 6 || (info.majorVersion == 6 && info.minorVersion <= 1)
+	// NT kernel handles are divisible by 4, with the bottom 3 bits left as
+	// a tag. The fully set tag correlates with the types of handles we're
+	// concerned about here.  Except, the kernel will interpret some
+	// special handle values, like -1, -2, and so forth, so kernelbase.dll
+	// checks to see that those bottom three bits are checked, but that top
+	// bit is not checked.
+	isLegacyWin7ConsoleHandle := func(handle Handle) bool { return isWin7 && handle&0x10000003 == 3 }
+
 	p, _ := GetCurrentProcess()
 	parentProcess := p
 	if sys.ParentProcess != 0 {
@@ -325,7 +336,15 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
 	fd := make([]Handle, len(attr.Files))
 	for i := range attr.Files {
 		if attr.Files[i] > 0 {
-			err := DuplicateHandle(p, Handle(attr.Files[i]), parentProcess, &fd[i], 0, true, DUPLICATE_SAME_ACCESS)
+			destinationProcessHandle := parentProcess
+
+			// On Windows 7, console handles aren't real handles, and can only be duplicated
+			// into the current process, not a parent one, which amounts to the same thing.
+			if parentProcess != p && isLegacyWin7ConsoleHandle(Handle(attr.Files[i])) {
+				destinationProcessHandle = p
+			}
+
+			err := DuplicateHandle(p, Handle(attr.Files[i]), destinationProcessHandle, &fd[i], 0, true, DUPLICATE_SAME_ACCESS)
 			if err != nil {
 				return 0, 0, err
 			}
@@ -356,6 +375,14 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
 
 	fd = append(fd, sys.AdditionalInheritedHandles...)
 
+	// On Windows 7, console handles aren't real handles, so don't pass them
+	// through to PROC_THREAD_ATTRIBUTE_HANDLE_LIST.
+	for i := range fd {
+		if isLegacyWin7ConsoleHandle(fd[i]) {
+			fd[i] = 0
+		}
+	}
+
 	// The presence of a NULL handle in the list is enough to cause PROC_THREAD_ATTRIBUTE_HANDLE_LIST
 	// to treat the entire list as empty, so remove NULL handles.
 	j := 0

src/syscall/types_windows.go

@@ -1169,3 +1169,13 @@ const (
 )
 
 const UNIX_PATH_MAX = 108 // defined in afunix.h
+
+// https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/ns-wdm-_osversioninfow
+type _OSVERSIONINFOW struct {
+	osVersionInfoSize uint32
+	majorVersion      uint32
+	minorVersion      uint32
+	buildNumber       uint32
+	platformId        uint32
+	csdVersion        [128]uint16
+}

src/syscall/zsyscall_windows.go

@@ -43,6 +43,7 @@ var (
 	modkernel32 = NewLazyDLL(sysdll.Add("kernel32.dll"))
 	modmswsock  = NewLazyDLL(sysdll.Add("mswsock.dll"))
 	modnetapi32 = NewLazyDLL(sysdll.Add("netapi32.dll"))
+	modntdll    = NewLazyDLL(sysdll.Add("ntdll.dll"))
 	modsecur32  = NewLazyDLL(sysdll.Add("secur32.dll"))
 	modshell32  = NewLazyDLL(sysdll.Add("shell32.dll"))
 	moduserenv  = NewLazyDLL(sysdll.Add("userenv.dll"))
@@ -169,6 +170,7 @@ var (
 	procNetGetJoinInformation              = modnetapi32.NewProc("NetGetJoinInformation")
 	procNetUserGetInfo                     = modnetapi32.NewProc("NetUserGetInfo")
 	procGetUserNameExW                     = modsecur32.NewProc("GetUserNameExW")
+	procRtlGetVersion                      = modntdll.NewProc("RtlGetVersion")
 	procTranslateNameW                     = modsecur32.NewProc("TranslateNameW")
 	procCommandLineToArgvW                 = modshell32.NewProc("CommandLineToArgvW")
 	procGetUserProfileDirectoryW           = moduserenv.NewProc("GetUserProfileDirectoryW")
@@ -1228,6 +1230,11 @@ func GetUserNameEx(nameFormat uint32, nameBuffre *uint16, nSize *uint32) (err er
 	return
 }
 
+func rtlGetVersion(info *_OSVERSIONINFOW) {
+	Syscall(procRtlGetVersion.Addr(), 1, uintptr(unsafe.Pointer(info)), 0, 0)
+	return
+}
+
 func TranslateName(accName *uint16, accNameFormat uint32, desiredNameFormat uint32, translatedName *uint16, nSize *uint32) (err error) {
 	r1, _, e1 := Syscall6(procTranslateNameW.Addr(), 5, uintptr(unsafe.Pointer(accName)), uintptr(accNameFormat), uintptr(desiredNameFormat), uintptr(unsafe.Pointer(translatedName)), uintptr(unsafe.Pointer(nSize)), 0)
 	if r1&0xff == 0 {

src/time/sleep_test.go

@@ -785,6 +785,68 @@ func TestAdjustTimers(t *testing.T) {
 	}
 }
 
+func TestStopResult(t *testing.T) {
+	testStopResetResult(t, true)
+}
+
+func TestResetResult(t *testing.T) {
+	testStopResetResult(t, false)
+}
+
+// Test that when racing between running a timer and stopping a timer Stop
+// consistently indicates whether a value can be read from the channel.
+// Issue #69312.
+func testStopResetResult(t *testing.T, testStop bool) {
+	for _, name := range []string{"0", "1", "2"} {
+		t.Run("asynctimerchan="+name, func(t *testing.T) {
+			testStopResetResultGODEBUG(t, testStop, name)
+		})
+	}
+}
+
+func testStopResetResultGODEBUG(t *testing.T, testStop bool, godebug string) {
+	t.Setenv("GODEBUG", "asynctimerchan="+godebug)
+
+	stopOrReset := func(timer *Timer) bool {
+		if testStop {
+			return timer.Stop()
+		} else {
+			return timer.Reset(1 * Hour)
+		}
+	}
+
+	start := make(chan struct{})
+	var wg sync.WaitGroup
+	const N = 1000
+	wg.Add(N)
+	for range N {
+		go func() {
+			defer wg.Done()
+			<-start
+			for j := 0; j < 100; j++ {
+				timer1 := NewTimer(1 * Millisecond)
+				timer2 := NewTimer(1 * Millisecond)
+				select {
+				case <-timer1.C:
+					if !stopOrReset(timer2) {
+						// The test fails if this
+						// channel read times out.
+						<-timer2.C
+					}
+				case <-timer2.C:
+					if !stopOrReset(timer1) {
+						// The test fails if this
+						// channel read times out.
+						<-timer1.C
+					}
+				}
+			}
+		}()
+	}
+	close(start)
+	wg.Wait()
+}
+
 // Benchmark timer latency when the thread that creates the timer is busy with
 // other work and the timers must be serviced by other threads.
 // https://golang.org/issue/38860

test/fixedbugs/issue69434.go

@@ -0,0 +1,173 @@
+// run
+
+// Copyright 2024 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.
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"iter"
+	"math/rand"
+	"os"
+	"strings"
+	"unicode"
+)
+
+// WordReader is the struct that implements io.Reader
+type WordReader struct {
+	scanner *bufio.Scanner
+}
+
+// NewWordReader creates a new WordReader from an io.Reader
+func NewWordReader(r io.Reader) *WordReader {
+	scanner := bufio.NewScanner(r)
+	scanner.Split(bufio.ScanWords)
+	return &WordReader{
+		scanner: scanner,
+	}
+}
+
+// Read reads data from the input stream and returns a single lowercase word at a time
+func (wr *WordReader) Read(p []byte) (n int, err error) {
+	if !wr.scanner.Scan() {
+		if err := wr.scanner.Err(); err != nil {
+			return 0, err
+		}
+		return 0, io.EOF
+	}
+	word := wr.scanner.Text()
+	cleanedWord := removeNonAlphabetic(word)
+	if len(cleanedWord) == 0 {
+		return wr.Read(p)
+	}
+	n = copy(p, []byte(cleanedWord))
+	return n, nil
+}
+
+// All returns an iterator allowing the caller to iterate over the WordReader using for/range.
+func (wr *WordReader) All() iter.Seq[string] {
+	word := make([]byte, 1024)
+	return func(yield func(string) bool) {
+		var err error
+		var n int
+		for n, err = wr.Read(word); err == nil; n, err = wr.Read(word) {
+			if !yield(string(word[:n])) {
+				return
+			}
+		}
+		if err != io.EOF {
+			fmt.Fprintf(os.Stderr, "error reading word: %v\n", err)
+		}
+	}
+}
+
+// removeNonAlphabetic removes non-alphabetic characters from a word using strings.Map
+func removeNonAlphabetic(word string) string {
+	return strings.Map(func(r rune) rune {
+		if unicode.IsLetter(r) {
+			return unicode.ToLower(r)
+		}
+		return -1
+	}, word)
+}
+
+// ProbabilisticSkipper determines if an item should be retained with probability 1/(1<<n)
+type ProbabilisticSkipper struct {
+	n       int
+	counter uint64
+	bitmask uint64
+}
+
+// NewProbabilisticSkipper initializes the ProbabilisticSkipper
+func NewProbabilisticSkipper(n int) *ProbabilisticSkipper {
+	pr := &ProbabilisticSkipper{n: n}
+	pr.refreshCounter()
+	return pr
+}
+
+// check panics if pr.n is not the expected value
+func (pr *ProbabilisticSkipper) check(n int) {
+	if pr.n != n {
+		panic(fmt.Sprintf("check: pr.n != n  %d != %d", pr.n, n))
+	}
+}
+
+// refreshCounter refreshes the counter with a new random value
+func (pr *ProbabilisticSkipper) refreshCounter() {
+	if pr.n == 0 {
+		pr.bitmask = ^uint64(0) // All bits set to 1
+	} else {
+		pr.bitmask = rand.Uint64()
+		for i := 0; i < pr.n-1; i++ {
+			pr.bitmask &= rand.Uint64()
+		}
+	}
+	pr.counter = 64
+}
+
+// ShouldSkip returns true with probability 1/(1<<n)
+func (pr *ProbabilisticSkipper) ShouldSkip() bool {
+	remove := pr.bitmask&1 == 0
+	pr.bitmask >>= 1
+	pr.counter--
+	if pr.counter == 0 {
+		pr.refreshCounter()
+	}
+	return remove
+}
+
+// EstimateUniqueWordsIter estimates the number of unique words using a probabilistic counting method
+func EstimateUniqueWordsIter(reader io.Reader, memorySize int) int {
+	wordReader := NewWordReader(reader)
+	words := make(map[string]struct{}, memorySize)
+
+	rounds := 0
+	roundRemover := NewProbabilisticSkipper(1)
+	wordSkipper := NewProbabilisticSkipper(rounds)
+	wordSkipper.check(rounds)
+
+	for word := range wordReader.All() {
+		wordSkipper.check(rounds)
+		if wordSkipper.ShouldSkip() {
+			delete(words, word)
+		} else {
+			words[word] = struct{}{}
+
+			if len(words) >= memorySize {
+				rounds++
+
+				wordSkipper = NewProbabilisticSkipper(rounds)
+				for w := range words {
+					if roundRemover.ShouldSkip() {
+						delete(words, w)
+					}
+				}
+			}
+		}
+		wordSkipper.check(rounds)
+	}
+
+	if len(words) == 0 {
+		return 0
+	}
+
+	invProbability := 1 << rounds
+	estimatedUniqueWords := len(words) * invProbability
+	return estimatedUniqueWords
+}
+
+func main() {
+	input := "Hello, world! This is a test. Hello, world, hello!"
+	expectedUniqueWords := 6 // "hello", "world", "this", "is", "a", "test" (but "hello" and "world" are repeated)
+	memorySize := 6
+
+	reader := strings.NewReader(input)
+	estimatedUniqueWords := EstimateUniqueWordsIter(reader, memorySize)
+	if estimatedUniqueWords != expectedUniqueWords {
+		// ...
+	}
+}

test/fixedbugs/issue69507.go

@@ -0,0 +1,133 @@
+// run
+
+// Copyright 2024 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.
+
+package main
+
+func main() {
+	err := run()
+	if err != nil {
+		panic(err)
+	}
+}
+
+func run() error {
+	methods := "AB"
+
+	type node struct {
+		tag     string
+		choices []string
+	}
+	all := []node{
+		{"000", permutations(methods)},
+	}
+
+	next := 1
+	for len(all) > 0 {
+		cur := all[0]
+		k := copy(all, all[1:])
+		all = all[:k]
+
+		if len(cur.choices) == 1 {
+			continue
+		}
+
+		var bestM map[byte][]string
+		bMax := len(cur.choices) + 1
+		bMin := -1
+		for sel := range selections(methods) {
+			m := make(map[byte][]string)
+			for _, order := range cur.choices {
+				x := findFirstMatch(order, sel)
+				m[x] = append(m[x], order)
+			}
+
+			min := len(cur.choices) + 1
+			max := -1
+			for _, v := range m {
+				if len(v) < min {
+					min = len(v)
+				}
+				if len(v) > max {
+					max = len(v)
+				}
+			}
+			if max < bMax || (max == bMax && min > bMin) {
+				bestM = m
+				bMin = min
+				bMax = max
+			}
+		}
+
+		if bMax == len(cur.choices) {
+			continue
+		}
+
+		cc := Keys(bestM)
+		for c := range cc {
+			choices := bestM[c]
+			next++
+
+			switch c {
+			case 'A':
+			case 'B':
+			default:
+				panic("unexpected selector type " + string(c))
+			}
+			all = append(all, node{"", choices})
+		}
+	}
+	return nil
+}
+
+func permutations(s string) []string {
+	if len(s) <= 1 {
+		return []string{s}
+	}
+
+	var result []string
+	for i, char := range s {
+		rest := s[:i] + s[i+1:]
+		for _, perm := range permutations(rest) {
+			result = append(result, string(char)+perm)
+		}
+	}
+	return result
+}
+
+type Seq[V any] func(yield func(V) bool)
+
+func selections(s string) Seq[string] {
+	return func(yield func(string) bool) {
+		for bits := 1; bits < 1<<len(s); bits++ {
+			var choice string
+			for j, char := range s {
+				if bits&(1<<j) != 0 {
+					choice += string(char)
+				}
+			}
+			if !yield(choice) {
+				break
+			}
+		}
+	}
+}
+
+func findFirstMatch(order, sel string) byte {
+	for _, c := range order {
+		return byte(c)
+	}
+	return 0
+}
+
+func Keys[Map ~map[K]V, K comparable, V any](m Map) Seq[K] {
+	return func(yield func(K) bool) {
+		for k := range m {
+			if !yield(k) {
+				return
+			}
+		}
+	}
+}