src/main/java/com/code_intelligence/jazzer/instrumentor/DeterministicRandom.kt


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// Copyright 2021 Code Intelligence GmbH
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.code_intelligence.jazzer.instrumentor

import java.security.MessageDigest
import java.security.SecureRandom

// This RNG is resistant to collisions (even under XOR) but fully deterministic.
internal class DeterministicRandom(vararg contexts: String) {
    private val random = SecureRandom.getInstance("SHA1PRNG").apply {
        val contextHash = MessageDigest.getInstance("SHA-256").run {
            for (context in contexts) {
                update(context.toByteArray())
            }
            digest()
        }
        setSeed(contextHash)
    }

    fun nextInt(bound: Int) = random.nextInt(bound)

    fun nextInt() = random.nextInt()
}