github.com/cespare/xxhash/v2 v2.1.1: Sum64

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify Sum64 in pkg:golang/github.com/cespare/xxhash/v2@v2.1.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/cespare/xxhash/v2@v2.1.1
Demonstrate these symbols/APIs:
  - Sum64
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:7d62c9064a527de528984da8ab2860633c918477be421ec092a0084ef2a6d381","contract":["xxhash.Sum64 computes deterministic 64-bit checksum for byte slices","xxhash.Sum64 produces different hashes for different byte slices","xxhash.Sum64 returns consistent deterministic hash for empty byte slice","xxhash.Sum64 with single byte slice matches expected calculation"],"goal":"verify Sum64 in pkg:golang/github.com/cespare/xxhash/v2@v2.1.1","kind":"HOW","packages":["pkg:golang/github.com/cespare/xxhash/v2@v2.1.1"],"schemaVersion":1,"symbols":["Sum64"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","ecosystem":"golang","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/cespare/xxhash/v2@v2.1.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/cespare/xxhash/v2@v2.1.1","symbols":["Sum64"],"verifierAdapter":"golang@1"}

module sample

go 1.26

require github.com/cespare/xxhash/v2 v2.1.1

github.com/cespare/xxhash/v2 v2.1.1 h1:6MnRN8NT7+YBpUIWxHtefFZOKTAPgGjpQSxqLNn0+qY=
github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=

package main

import (
	"fmt"

	"github.com/cespare/xxhash/v2"
)

// HashBytes computes the 64-bit xxHash checksum of a byte slice.
func HashBytes(b []byte) uint64 {
	return xxhash.Sum64(b)
}

func main() {
	data := []byte("hello world")
	hash := HashBytes(data)
	fmt.Printf("Sum64: %d\n", hash)
}

{
  "schemaVersion": 1,
  "goal": "verify Sum64 in pkg:golang/github.com/cespare/xxhash/v2@v2.1.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/cespare/xxhash/v2@v2.1.1"
  ],
  "symbols": [
    "Sum64"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"fmt"
	"os"

	"github.com/cespare/xxhash/v2"
)

func assertTrue(name string, condition bool) {
	if !condition {
		fmt.Fprintf(os.Stderr, "Assertion failed for %s: expected true, got false\n", name)
		os.Exit(1)
	}
}

func assertEqualUint64(name string, actual, expected uint64) {
	if actual != expected {
		fmt.Fprintf(os.Stderr, "Assertion failed for %s: got %d, expected %d\n", name, actual, expected)
		os.Exit(1)
	}
}

func main() {
	// Contract: xxhash.Sum64 computes deterministic 64-bit checksum for byte slices
	bytesInput := []byte("CodeSampleX xxhash test payload")
	hash1 := xxhash.Sum64(bytesInput)
	hash2 := xxhash.Sum64(bytesInput)
	assertEqualUint64("xxhash.Sum64 returns consistent hash", hash1, hash2)
	assertTrue("xxhash.Sum64 returns non-zero hash", hash1 != 0)

	// Contract: xxhash.Sum64 produces different hashes for different byte slices
	differentInput := []byte("Different payload")
	diffHash := xxhash.Sum64(differentInput)
	assertTrue("different input produces different hash", diffHash != hash1)

	// Contract: xxhash.Sum64 returns consistent deterministic hash for empty byte slice
	emptyHash1 := xxhash.Sum64([]byte{})
	emptyHash2 := xxhash.Sum64([]byte{})
	assertEqualUint64("empty slice returns consistent hash", emptyHash1, emptyHash2)
	assertTrue("empty slice returns non-zero hash", emptyHash1 != 0)

	// Contract: xxhash.Sum64 with single byte slice matches expected calculation
	singleByteHash := xxhash.Sum64([]byte{0x42})
	assertTrue("single byte returns valid hash", singleByteHash != 0)

	fmt.Println("All contract assertions passed successfully.")
}