src/crypto/internal/randutil/randutil.go

// Copyright 2018 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.

// Package randutil contains internal randomness utilities for various
// crypto packages.
package randutil

import (
	"io"
	"math/rand/v2"
)

// MaybeReadByte reads a single byte from r with 50% probability. This is used
// to ensure that callers do not depend on non-guaranteed behaviour, e.g.
// assuming that rsa.GenerateKey is deterministic w.r.t. a given random stream.
//
// This does not affect tests that pass a stream of fixed bytes as the random
// source (e.g. a zeroReader).
func MaybeReadByte(r io.Reader) {
	if rand.Uint64()&1 == 1 {
		return
	}
	var buf [1]byte
	r.Read(buf[:])
}