github.com/cockroachdb/cockroach@v20.2.0-alpha.1+incompatible/pkg/workload/workloadimpl/random.go (about)

     1  // Copyright 2019 The Cockroach Authors.
     2  //
     3  // Use of this software is governed by the Business Source License
     4  // included in the file licenses/BSL.txt.
     5  //
     6  // As of the Change Date specified in that file, in accordance with
     7  // the Business Source License, use of this software will be governed
     8  // by the Apache License, Version 2.0, included in the file
     9  // licenses/APL.txt.
    10  
    11  package workloadimpl
    12  
    13  import (
    14  	"math"
    15  
    16  	"golang.org/x/exp/rand"
    17  )
    18  
    19  // RandStringFast is a non-specialized random string generator with an even
    20  // distribution of alphabet in the output.
    21  func RandStringFast(rng rand.Source, buf []byte, alphabet string) {
    22  	// We could pull these computations out to be done once per alphabet, but at
    23  	// that point, you likely should consider PrecomputedRand.
    24  	alphabetLen := uint64(len(alphabet))
    25  	// floor(log(math.MaxUint64)/log(alphabetLen))
    26  	lettersCharsPerRand := uint64(math.Log(float64(math.MaxUint64)) / math.Log(float64(alphabetLen)))
    27  
    28  	var r, charsLeft uint64
    29  	for i := 0; i < len(buf); i++ {
    30  		if charsLeft == 0 {
    31  			r = rng.Uint64()
    32  			charsLeft = lettersCharsPerRand
    33  		}
    34  		buf[i] = alphabet[r%alphabetLen]
    35  		r = r / alphabetLen
    36  		charsLeft--
    37  	}
    38  }