github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2: Fingerprint128

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 github.com/dgryski/go-farm.Fingerprint128 in pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2
Demonstrate these symbols/APIs:
  - github.com/dgryski/go-farm.Fingerprint128
Required runtime conditions:
  - ecosystem: golang
  - language: go
  - packageManager: go@1.26.6
  - runtime: go@1.26.6

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:c6c0fba6049ace23673b6962602f45e489e5ce36559571f0cb1dfaff76889546","contract":["farm.Fingerprint128 computes deterministic 128-bit lo and hi components for byte slices","farm.Fingerprint128 produces distinct 128-bit fingerprints for differing inputs without collision","farm.Fingerprint128 matches reference FarmHash test vectors for empty and standard inputs","farm.Fingerprint128 handles sub-slice inputs consistently with identical byte content"],"goal":"verify github.com/dgryski/go-farm.Fingerprint128 in pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2","kind":"HOW","packages":["pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2"],"schemaVersion":1,"symbols":["github.com/dgryski/go-farm.Fingerprint128"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2"],"schemaVersion":1,"subject":"pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2","symbols":["github.com/dgryski/go-farm.Fingerprint128"],"verifierAdapter":"golang@1"}

module example.com/farm-fingerprint128

go 1.22.0

require github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2

github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2 h1:tdlZCpZ/P9DhczCTSixgIKmwPv6+wP5DGjqLYw5SUiA=
github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2/go.mod h1:SqUrOPUnsFjfmXRMNPybcSiG0BgUW2AuFH8PAnS2iTw=

package main

import (
	"fmt"

	farm "github.com/dgryski/go-farm"
)

// ComputeFingerprint128 returns the low and high 64-bit halves of the 128-bit FarmHash fingerprint.
func ComputeFingerprint128(data []byte) (lo, hi uint64) {
	return farm.Fingerprint128(data)
}

// FormatFingerprint128 returns a 32-character hex representation of the 128-bit fingerprint.
func FormatFingerprint128(lo, hi uint64) string {
	return fmt.Sprintf("%016x%016x", hi, lo)
}

func main() {
	input := []byte("hello farmhash")
	lo, hi := ComputeFingerprint128(input)
	fmt.Printf("Fingerprint128: %s (lo=%#016x, hi=%#016x)\n", FormatFingerprint128(lo, hi), lo, hi)
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/dgryski/go-farm.Fingerprint128 in pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/dgryski/go-farm@v0.0.0-20190423205320-6a90982ecee2"
  ],
  "symbols": [
    "github.com/dgryski/go-farm.Fingerprint128"
  ],
  "runtimeConditions": {
    "ecosystem": "golang",
    "language": "go",
    "packageManager": "go@1.26.6",
    "runtime": "go@1.26.6"
  }
}

package main

import (
	"bytes"
	"fmt"
	"os"

	farm "github.com/dgryski/go-farm"
)

func main() {
	// Assertion 1: farm.Fingerprint128 computes deterministic 128-bit lo and hi components for byte slices
	input1 := []byte("The quick brown fox jumps over the lazy dog.")
	lo1a, hi1a := farm.Fingerprint128(input1)
	lo1b, hi1b := farm.Fingerprint128(input1)
	if lo1a != lo1b || hi1a != hi1b {
		fmt.Fprintf(os.Stderr, "FAIL: Fingerprint128 is not deterministic: (%#x, %#x) != (%#x, %#x)\n", lo1a, hi1a, lo1b, hi1b)
		os.Exit(1)
	}

	// Assertion 2: farm.Fingerprint128 produces distinct 128-bit fingerprints for differing inputs without collision
	input2 := []byte("The quick brown fox jumps over the lazy cog.")
	lo2, hi2 := farm.Fingerprint128(input2)
	if lo1a == lo2 && hi1a == hi2 {
		fmt.Fprintf(os.Stderr, "FAIL: Fingerprint128 collision on distinct inputs: (%#x, %#x)\n", lo1a, hi1a)
		os.Exit(1)
	}

	diffPairs := [][2]string{
		{"sample-key-alpha", "sample-key-beta"},
		{"user:1001:session", "user:1002:session"},
		{"data/chunk/0001", "data/chunk/0002"},
	}
	for _, pair := range diffPairs {
		lA, hA := farm.Fingerprint128([]byte(pair[0]))
		lB, hB := farm.Fingerprint128([]byte(pair[1]))
		if lA == lB && hA == hB {
			fmt.Fprintf(os.Stderr, "FAIL: Fingerprint128 collision between %q and %q\n", pair[0], pair[1])
			os.Exit(1)
		}
	}

	// Assertion 3: farm.Fingerprint128 matches reference FarmHash test vectors for empty and standard inputs
	vectors := []struct {
		in   string
		wantLo uint64
		wantHi uint64
	}{
		{"", 0x3df09dfc64c09a2b, 0x3cb540c392e51e29},
		{"a", 0x6e97d6bbdfc0a0c4, 0x52a71e38f43be561},
		{"ab", 0x13e834f38a6c88b8, 0xcfdbce01c0e7622e},
		{"abc", 0x3980b2afd2126c04, 0xa085f09013029e45},
		{"abcd", 0xb8d7175e11647e82, 0x0906d778016538d9},
		{"0123456789", 0xcf650cdfad0d0675, 0x6f6cb496e4b429c5},
	}
	for _, vec := range vectors {
		gotLo, gotHi := farm.Fingerprint128([]byte(vec.in))
		if gotLo != vec.wantLo || gotHi != vec.wantHi {
			fmt.Fprintf(os.Stderr, "FAIL: Fingerprint128(%q) = (%#016x, %#016x), want (%#016x, %#016x)\n",
				vec.in, gotLo, gotHi, vec.wantLo, vec.wantHi)
			os.Exit(1)
		}
	}

	// Assertion 4: farm.Fingerprint128 handles sub-slice inputs consistently with identical byte content
	base := []byte("prefix-0123456789-suffix")
	subSlice := base[7:17] // "0123456789"
	standalone := []byte("0123456789")
	if !bytes.Equal(subSlice, standalone) {
		fmt.Fprintf(os.Stderr, "FAIL: test setup issue: bytes not equal\n")
		os.Exit(1)
	}
	subLo, subHi := farm.Fingerprint128(subSlice)
	stdLo, stdHi := farm.Fingerprint128(standalone)
	if subLo != stdLo || subHi != stdHi {
		fmt.Fprintf(os.Stderr, "FAIL: Fingerprint128 on sub-slice mismatch: (%#x, %#x) != (%#x, %#x)\n",
			subLo, subHi, stdLo, stdHi)
		os.Exit(1)
	}

	fmt.Println("PASS: farm.Fingerprint128 contract passed")
}