From 677b6cc17544e5e667d4bb67d063f5d775c69e32 Mon Sep 17 00:00:00 2001
From: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Date: Thu, 26 Sep 2024 01:37:07 +0700
Subject: [PATCH] test: simplify issue 69434 test

Updates #69434

Change-Id: I780c5ed63561eb8fa998bb0e6cdc77a904ff29c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/615915
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---
 test/fixedbugs/issue69434.go | 164 +++++------------------------------
 1 file changed, 22 insertions(+), 142 deletions(-)

diff --git a/test/fixedbugs/issue69434.go b/test/fixedbugs/issue69434.go
index 68204660196..6443bde50f8 100644
--- a/test/fixedbugs/issue69434.go
+++ b/test/fixedbugs/issue69434.go
@@ -1,4 +1,4 @@
-// run
+// run -gcflags=-d=maymorestack=runtime.mayMoreStackMove
 
 // Copyright 2024 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,167 +7,47 @@
 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])) {
+func All() iter.Seq[int] {
+	return func(yield func(int) bool) {
+		for i := 0; i < 10; i++ {
+			if !yield(i) {
 				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)
+type S struct {
+	round int
 }
 
-// ProbabilisticSkipper determines if an item should be retained with probability 1/(1<<n)
-type ProbabilisticSkipper struct {
-	n       int
-	counter uint64
-	bitmask uint64
+func NewS(round int) *S {
+	s := &S{round: round}
+	return s
 }
 
-// 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))
+func (s *S) check(round int) {
+	if s.round != round {
+		panic("bad round")
 	}
 }
 
-// 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)
-
+func f() {
 	rounds := 0
-	roundRemover := NewProbabilisticSkipper(1)
-	wordSkipper := NewProbabilisticSkipper(rounds)
-	wordSkipper.check(rounds)
+	s := NewS(rounds)
+	s.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)
+	for range All() {
+		s.check(rounds)
+		rounds++
+		s = NewS(rounds)
+		s.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 {
-		// ...
-	}
+	f()
 }