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-rw-r--r--src/hash/maphash/smhasher_test.go474
1 files changed, 474 insertions, 0 deletions
diff --git a/src/hash/maphash/smhasher_test.go b/src/hash/maphash/smhasher_test.go
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+++ b/src/hash/maphash/smhasher_test.go
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+// Copyright 2019 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.
+
+//go:build !race
+
+package maphash
+
+import (
+ "fmt"
+ "math"
+ "math/rand"
+ "runtime"
+ "strings"
+ "testing"
+ "unsafe"
+)
+
+// Smhasher is a torture test for hash functions.
+// https://code.google.com/p/smhasher/
+// This code is a port of some of the Smhasher tests to Go.
+
+// Note: due to the long running time of these tests, they are
+// currently disabled in -race mode.
+
+var fixedSeed = MakeSeed()
+
+// Sanity checks.
+// hash should not depend on values outside key.
+// hash should not depend on alignment.
+func TestSmhasherSanity(t *testing.T) {
+ r := rand.New(rand.NewSource(1234))
+ const REP = 10
+ const KEYMAX = 128
+ const PAD = 16
+ const OFFMAX = 16
+ for k := 0; k < REP; k++ {
+ for n := 0; n < KEYMAX; n++ {
+ for i := 0; i < OFFMAX; i++ {
+ var b [KEYMAX + OFFMAX + 2*PAD]byte
+ var c [KEYMAX + OFFMAX + 2*PAD]byte
+ randBytes(r, b[:])
+ randBytes(r, c[:])
+ copy(c[PAD+i:PAD+i+n], b[PAD:PAD+n])
+ if bytesHash(b[PAD:PAD+n]) != bytesHash(c[PAD+i:PAD+i+n]) {
+ t.Errorf("hash depends on bytes outside key")
+ }
+ }
+ }
+ }
+}
+
+func bytesHash(b []byte) uint64 {
+ var h Hash
+ h.SetSeed(fixedSeed)
+ h.Write(b)
+ return h.Sum64()
+}
+func stringHash(s string) uint64 {
+ var h Hash
+ h.SetSeed(fixedSeed)
+ h.WriteString(s)
+ return h.Sum64()
+}
+
+const hashSize = 64
+
+func randBytes(r *rand.Rand, b []byte) {
+ r.Read(b) // can't fail
+}
+
+// A hashSet measures the frequency of hash collisions.
+type hashSet struct {
+ m map[uint64]struct{} // set of hashes added
+ n int // number of hashes added
+}
+
+func newHashSet() *hashSet {
+ return &hashSet{make(map[uint64]struct{}), 0}
+}
+func (s *hashSet) add(h uint64) {
+ s.m[h] = struct{}{}
+ s.n++
+}
+func (s *hashSet) addS(x string) {
+ s.add(stringHash(x))
+}
+func (s *hashSet) addB(x []byte) {
+ s.add(bytesHash(x))
+}
+func (s *hashSet) addS_seed(x string, seed Seed) {
+ var h Hash
+ h.SetSeed(seed)
+ h.WriteString(x)
+ s.add(h.Sum64())
+}
+func (s *hashSet) check(t *testing.T) {
+ const SLOP = 10.0
+ collisions := s.n - len(s.m)
+ pairs := int64(s.n) * int64(s.n-1) / 2
+ expected := float64(pairs) / math.Pow(2.0, float64(hashSize))
+ stddev := math.Sqrt(expected)
+ if float64(collisions) > expected+SLOP*(3*stddev+1) {
+ t.Errorf("unexpected number of collisions: got=%d mean=%f stddev=%f", collisions, expected, stddev)
+ }
+}
+
+// a string plus adding zeros must make distinct hashes
+func TestSmhasherAppendedZeros(t *testing.T) {
+ s := "hello" + strings.Repeat("\x00", 256)
+ h := newHashSet()
+ for i := 0; i <= len(s); i++ {
+ h.addS(s[:i])
+ }
+ h.check(t)
+}
+
+// All 0-3 byte strings have distinct hashes.
+func TestSmhasherSmallKeys(t *testing.T) {
+ h := newHashSet()
+ var b [3]byte
+ for i := 0; i < 256; i++ {
+ b[0] = byte(i)
+ h.addB(b[:1])
+ for j := 0; j < 256; j++ {
+ b[1] = byte(j)
+ h.addB(b[:2])
+ if !testing.Short() {
+ for k := 0; k < 256; k++ {
+ b[2] = byte(k)
+ h.addB(b[:3])
+ }
+ }
+ }
+ }
+ h.check(t)
+}
+
+// Different length strings of all zeros have distinct hashes.
+func TestSmhasherZeros(t *testing.T) {
+ N := 256 * 1024
+ if testing.Short() {
+ N = 1024
+ }
+ h := newHashSet()
+ b := make([]byte, N)
+ for i := 0; i <= N; i++ {
+ h.addB(b[:i])
+ }
+ h.check(t)
+}
+
+// Strings with up to two nonzero bytes all have distinct hashes.
+func TestSmhasherTwoNonzero(t *testing.T) {
+ if runtime.GOARCH == "wasm" {
+ t.Skip("Too slow on wasm")
+ }
+ if testing.Short() {
+ t.Skip("Skipping in short mode")
+ }
+ h := newHashSet()
+ for n := 2; n <= 16; n++ {
+ twoNonZero(h, n)
+ }
+ h.check(t)
+}
+func twoNonZero(h *hashSet, n int) {
+ b := make([]byte, n)
+
+ // all zero
+ h.addB(b)
+
+ // one non-zero byte
+ for i := 0; i < n; i++ {
+ for x := 1; x < 256; x++ {
+ b[i] = byte(x)
+ h.addB(b)
+ b[i] = 0
+ }
+ }
+
+ // two non-zero bytes
+ for i := 0; i < n; i++ {
+ for x := 1; x < 256; x++ {
+ b[i] = byte(x)
+ for j := i + 1; j < n; j++ {
+ for y := 1; y < 256; y++ {
+ b[j] = byte(y)
+ h.addB(b)
+ b[j] = 0
+ }
+ }
+ b[i] = 0
+ }
+ }
+}
+
+// Test strings with repeats, like "abcdabcdabcdabcd..."
+func TestSmhasherCyclic(t *testing.T) {
+ if testing.Short() {
+ t.Skip("Skipping in short mode")
+ }
+ r := rand.New(rand.NewSource(1234))
+ const REPEAT = 8
+ const N = 1000000
+ for n := 4; n <= 12; n++ {
+ h := newHashSet()
+ b := make([]byte, REPEAT*n)
+ for i := 0; i < N; i++ {
+ b[0] = byte(i * 79 % 97)
+ b[1] = byte(i * 43 % 137)
+ b[2] = byte(i * 151 % 197)
+ b[3] = byte(i * 199 % 251)
+ randBytes(r, b[4:n])
+ for j := n; j < n*REPEAT; j++ {
+ b[j] = b[j-n]
+ }
+ h.addB(b)
+ }
+ h.check(t)
+ }
+}
+
+// Test strings with only a few bits set
+func TestSmhasherSparse(t *testing.T) {
+ if runtime.GOARCH == "wasm" {
+ t.Skip("Too slow on wasm")
+ }
+ if testing.Short() {
+ t.Skip("Skipping in short mode")
+ }
+ sparse(t, 32, 6)
+ sparse(t, 40, 6)
+ sparse(t, 48, 5)
+ sparse(t, 56, 5)
+ sparse(t, 64, 5)
+ sparse(t, 96, 4)
+ sparse(t, 256, 3)
+ sparse(t, 2048, 2)
+}
+func sparse(t *testing.T, n int, k int) {
+ b := make([]byte, n/8)
+ h := newHashSet()
+ setbits(h, b, 0, k)
+ h.check(t)
+}
+
+// set up to k bits at index i and greater
+func setbits(h *hashSet, b []byte, i int, k int) {
+ h.addB(b)
+ if k == 0 {
+ return
+ }
+ for j := i; j < len(b)*8; j++ {
+ b[j/8] |= byte(1 << uint(j&7))
+ setbits(h, b, j+1, k-1)
+ b[j/8] &= byte(^(1 << uint(j&7)))
+ }
+}
+
+// Test all possible combinations of n blocks from the set s.
+// "permutation" is a bad name here, but it is what Smhasher uses.
+func TestSmhasherPermutation(t *testing.T) {
+ if runtime.GOARCH == "wasm" {
+ t.Skip("Too slow on wasm")
+ }
+ if testing.Short() {
+ t.Skip("Skipping in short mode")
+ }
+ permutation(t, []uint32{0, 1, 2, 3, 4, 5, 6, 7}, 8)
+ permutation(t, []uint32{0, 1 << 29, 2 << 29, 3 << 29, 4 << 29, 5 << 29, 6 << 29, 7 << 29}, 8)
+ permutation(t, []uint32{0, 1}, 20)
+ permutation(t, []uint32{0, 1 << 31}, 20)
+ permutation(t, []uint32{0, 1, 2, 3, 4, 5, 6, 7, 1 << 29, 2 << 29, 3 << 29, 4 << 29, 5 << 29, 6 << 29, 7 << 29}, 6)
+}
+func permutation(t *testing.T, s []uint32, n int) {
+ b := make([]byte, n*4)
+ h := newHashSet()
+ genPerm(h, b, s, 0)
+ h.check(t)
+}
+func genPerm(h *hashSet, b []byte, s []uint32, n int) {
+ h.addB(b[:n])
+ if n == len(b) {
+ return
+ }
+ for _, v := range s {
+ b[n] = byte(v)
+ b[n+1] = byte(v >> 8)
+ b[n+2] = byte(v >> 16)
+ b[n+3] = byte(v >> 24)
+ genPerm(h, b, s, n+4)
+ }
+}
+
+type key interface {
+ clear() // set bits all to 0
+ random(r *rand.Rand) // set key to something random
+ bits() int // how many bits key has
+ flipBit(i int) // flip bit i of the key
+ hash() uint64 // hash the key
+ name() string // for error reporting
+}
+
+type bytesKey struct {
+ b []byte
+}
+
+func (k *bytesKey) clear() {
+ for i := range k.b {
+ k.b[i] = 0
+ }
+}
+func (k *bytesKey) random(r *rand.Rand) {
+ randBytes(r, k.b)
+}
+func (k *bytesKey) bits() int {
+ return len(k.b) * 8
+}
+func (k *bytesKey) flipBit(i int) {
+ k.b[i>>3] ^= byte(1 << uint(i&7))
+}
+func (k *bytesKey) hash() uint64 {
+ return bytesHash(k.b)
+}
+func (k *bytesKey) name() string {
+ return fmt.Sprintf("bytes%d", len(k.b))
+}
+
+// Flipping a single bit of a key should flip each output bit with 50% probability.
+func TestSmhasherAvalanche(t *testing.T) {
+ if runtime.GOARCH == "wasm" {
+ t.Skip("Too slow on wasm")
+ }
+ if testing.Short() {
+ t.Skip("Skipping in short mode")
+ }
+ avalancheTest1(t, &bytesKey{make([]byte, 2)})
+ avalancheTest1(t, &bytesKey{make([]byte, 4)})
+ avalancheTest1(t, &bytesKey{make([]byte, 8)})
+ avalancheTest1(t, &bytesKey{make([]byte, 16)})
+ avalancheTest1(t, &bytesKey{make([]byte, 32)})
+ avalancheTest1(t, &bytesKey{make([]byte, 200)})
+}
+func avalancheTest1(t *testing.T, k key) {
+ const REP = 100000
+ r := rand.New(rand.NewSource(1234))
+ n := k.bits()
+
+ // grid[i][j] is a count of whether flipping
+ // input bit i affects output bit j.
+ grid := make([][hashSize]int, n)
+
+ for z := 0; z < REP; z++ {
+ // pick a random key, hash it
+ k.random(r)
+ h := k.hash()
+
+ // flip each bit, hash & compare the results
+ for i := 0; i < n; i++ {
+ k.flipBit(i)
+ d := h ^ k.hash()
+ k.flipBit(i)
+
+ // record the effects of that bit flip
+ g := &grid[i]
+ for j := 0; j < hashSize; j++ {
+ g[j] += int(d & 1)
+ d >>= 1
+ }
+ }
+ }
+
+ // Each entry in the grid should be about REP/2.
+ // More precisely, we did N = k.bits() * hashSize experiments where
+ // each is the sum of REP coin flips. We want to find bounds on the
+ // sum of coin flips such that a truly random experiment would have
+ // all sums inside those bounds with 99% probability.
+ N := n * hashSize
+ var c float64
+ // find c such that Prob(mean-c*stddev < x < mean+c*stddev)^N > .9999
+ for c = 0.0; math.Pow(math.Erf(c/math.Sqrt(2)), float64(N)) < .9999; c += .1 {
+ }
+ c *= 4.0 // allowed slack - we don't need to be perfectly random
+ mean := .5 * REP
+ stddev := .5 * math.Sqrt(REP)
+ low := int(mean - c*stddev)
+ high := int(mean + c*stddev)
+ for i := 0; i < n; i++ {
+ for j := 0; j < hashSize; j++ {
+ x := grid[i][j]
+ if x < low || x > high {
+ t.Errorf("bad bias for %s bit %d -> bit %d: %d/%d\n", k.name(), i, j, x, REP)
+ }
+ }
+ }
+}
+
+// All bit rotations of a set of distinct keys
+func TestSmhasherWindowed(t *testing.T) {
+ windowed(t, &bytesKey{make([]byte, 128)})
+}
+func windowed(t *testing.T, k key) {
+ if runtime.GOARCH == "wasm" {
+ t.Skip("Too slow on wasm")
+ }
+ if testing.Short() {
+ t.Skip("Skipping in short mode")
+ }
+ const BITS = 16
+
+ for r := 0; r < k.bits(); r++ {
+ h := newHashSet()
+ for i := 0; i < 1<<BITS; i++ {
+ k.clear()
+ for j := 0; j < BITS; j++ {
+ if i>>uint(j)&1 != 0 {
+ k.flipBit((j + r) % k.bits())
+ }
+ }
+ h.add(k.hash())
+ }
+ h.check(t)
+ }
+}
+
+// All keys of the form prefix + [A-Za-z0-9]*N + suffix.
+func TestSmhasherText(t *testing.T) {
+ if testing.Short() {
+ t.Skip("Skipping in short mode")
+ }
+ text(t, "Foo", "Bar")
+ text(t, "FooBar", "")
+ text(t, "", "FooBar")
+}
+func text(t *testing.T, prefix, suffix string) {
+ const N = 4
+ const S = "ABCDEFGHIJKLMNOPQRSTabcdefghijklmnopqrst0123456789"
+ const L = len(S)
+ b := make([]byte, len(prefix)+N+len(suffix))
+ copy(b, prefix)
+ copy(b[len(prefix)+N:], suffix)
+ h := newHashSet()
+ c := b[len(prefix):]
+ for i := 0; i < L; i++ {
+ c[0] = S[i]
+ for j := 0; j < L; j++ {
+ c[1] = S[j]
+ for k := 0; k < L; k++ {
+ c[2] = S[k]
+ for x := 0; x < L; x++ {
+ c[3] = S[x]
+ h.addB(b)
+ }
+ }
+ }
+ }
+ h.check(t)
+}
+
+// Make sure different seed values generate different hashes.
+func TestSmhasherSeed(t *testing.T) {
+ if unsafe.Sizeof(uintptr(0)) == 4 {
+ t.Skip("32-bit platforms don't have ideal seed-input distributions (see issue 33988)")
+ }
+ h := newHashSet()
+ const N = 100000
+ s := "hello"
+ for i := 0; i < N; i++ {
+ h.addS_seed(s, Seed{s: uint64(i + 1)})
+ h.addS_seed(s, Seed{s: uint64(i+1) << 32}) // make sure high bits are used
+ }
+ h.check(t)
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-08-27 05:00:46 +0000