github.com/klauspost/compress v1.19.1: Estimate

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/klauspost/compress.Estimate in pkg:golang/github.com/klauspost/compress@v1.19.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/klauspost/compress@v1.19.1
Demonstrate these symbols/APIs:
  - github.com/klauspost/compress.Estimate

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:sha256:30df9107f7a9e8d75dbadf62128ef6650f28ad9646191614d00ba1526d6e38e8","contract":["compress.Estimate returns 0 for inputs shorter than 16 bytes","compress.Estimate returns score above 0.1 for repetitive text patterns","compress.Estimate returns score above 0.5 for highly compressible data like zeroes or repeated bytes","compress.Estimate returns score below 0.1 for high-entropy pseudo-random bytes","compress.Estimate ranks compressible data higher than high-entropy data"],"goal":"verify github.com/klauspost/compress.Estimate in pkg:golang/github.com/klauspost/compress@v1.19.1","kind":"HOW","packages":["pkg:golang/github.com/klauspost/compress@v1.19.1"],"schemaVersion":1,"symbols":["github.com/klauspost/compress.Estimate"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/klauspost/compress@v1.19.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/klauspost/compress@v1.19.1","symbols":["github.com/klauspost/compress.Estimate"],"verifierAdapter":"golang@1"}

package sample

import (
	"github.com/klauspost/compress"
)

// Estimate returns a normalized compressibility estimate of block b using compress.Estimate.
// Values close to zero are likely uncompressible.
// Values above 0.1 are likely to be compressible.
// Values above 0.5 are very compressible.
// Very small lengths (< 16) return 0.
func Estimate(b []byte) float64 {
	return compress.Estimate(b)
}

// IsCompressible reports whether the given data is estimated to be compressible (score >= 0.1).
func IsCompressible(b []byte) bool {
	return compress.Estimate(b) >= 0.1
}

// IsHighlyCompressible reports whether the given data is estimated to be highly compressible (score >= 0.5).
func IsHighlyCompressible(b []byte) bool {
	return compress.Estimate(b) >= 0.5
}

module sample

go 1.26.6

require github.com/klauspost/compress v1.19.1

github.com/klauspost/compress v1.19.1 h1:VsB4HPswih7mmZ8WleSFQ75c/Ui1M4trX5oAsJnhSlk=
github.com/klauspost/compress v1.19.1/go.mod h1:cwPg85FWrGar70rWktvGQj8/hthj3wpl0PGDogxkrSQ=

{
  "schemaVersion": 1,
  "goal": "verify github.com/klauspost/compress.Estimate in pkg:golang/github.com/klauspost/compress@v1.19.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/klauspost/compress@v1.19.1"
  ],
  "symbols": [
    "github.com/klauspost/compress.Estimate"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"github.com/klauspost/compress"
	"sample"
)

func main() {
	// Assertion 1: compress.Estimate returns 0 for inputs shorter than 16 bytes
	shortInputs := [][]byte{
		nil,
		{},
		[]byte("short"),
		[]byte("123456789012345"), // 15 bytes
	}
	for _, input := range shortInputs {
		score := compress.Estimate(input)
		if score != 0 {
			fmt.Fprintf(os.Stderr, "FAIL: expected 0 for input length %d, got %f\n", len(input), score)
			os.Exit(1)
		}
	}

	// Assertion 2: compress.Estimate returns score above 0.1 for repetitive text patterns
	repetitiveText := bytes.Repeat([]byte("repeating-pattern-"), 50)
	scoreRepetitive := sample.Estimate(repetitiveText)
	if scoreRepetitive <= 0.1 {
		fmt.Fprintf(os.Stderr, "FAIL: expected repetitive score > 0.1, got %f\n", scoreRepetitive)
		os.Exit(1)
	}
	if !sample.IsCompressible(repetitiveText) {
		fmt.Fprintf(os.Stderr, "FAIL: expected IsCompressible true for repetitive text\n")
		os.Exit(1)
	}

	// Assertion 3: compress.Estimate returns score above 0.5 for highly compressible data like zeroes or repeated bytes
	zeroes := make([]byte, 500)
	scoreZeroes := sample.Estimate(zeroes)
	if scoreZeroes <= 0.5 {
		fmt.Fprintf(os.Stderr, "FAIL: expected zeroes score > 0.5, got %f\n", scoreZeroes)
		os.Exit(1)
	}
	if !sample.IsHighlyCompressible(zeroes) {
		fmt.Fprintf(os.Stderr, "FAIL: expected IsHighlyCompressible true for zeroes\n")
		os.Exit(1)
	}

	homogeneous := bytes.Repeat([]byte{'X'}, 256)
	scoreHomogeneous := sample.Estimate(homogeneous)
	if scoreHomogeneous <= 0.8 {
		fmt.Fprintf(os.Stderr, "FAIL: expected homogeneous score > 0.8, got %f\n", scoreHomogeneous)
		os.Exit(1)
	}

	// Assertion 4: compress.Estimate returns score below 0.1 for high-entropy pseudo-random bytes
	randomData := make([]byte, 512)
	var state uint32 = 123456789
	for i := range randomData {
		state = state*1664525 + 1013904223
		randomData[i] = byte(state >> 24)
	}
	scoreRandom := sample.Estimate(randomData)
	if scoreRandom >= 0.1 {
		fmt.Fprintf(os.Stderr, "FAIL: expected high-entropy score < 0.1, got %f\n", scoreRandom)
		os.Exit(1)
	}
	if sample.IsCompressible(randomData) {
		fmt.Fprintf(os.Stderr, "FAIL: expected IsCompressible false for high-entropy data, got score %f\n", scoreRandom)
		os.Exit(1)
	}

	// Assertion 5: compress.Estimate ranks compressible data higher than high-entropy data
	if scoreRepetitive <= scoreRandom {
		fmt.Fprintf(os.Stderr, "FAIL: expected repetitive score (%f) > random score (%f)\n", scoreRepetitive, scoreRandom)
		os.Exit(1)
	}
	if scoreZeroes <= scoreRandom {
		fmt.Fprintf(os.Stderr, "FAIL: expected zeroes score (%f) > random score (%f)\n", scoreZeroes, scoreRandom)
		os.Exit(1)
	}

	fmt.Println("PASS: verify github.com/klauspost/compress.Estimate contract passed")
}