// Copyright 2017 PingCAP, Inc. // // 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, // See the License for the specific language governing permissions and // limitations under the License. package fastrand import ( _ "unsafe" // required by go:linkname ) // Buf generates a random string using ASCII characters but avoid separator character. // See https://github.com/mysql/mysql-server/blob/5.7/mysys_ssl/crypt_genhash_impl.cc#L435 func Buf(size int) []byte { buf := make([]byte, size) for i := 0; i < size; i++ { buf[i] = byte(Uint32N(127)) if buf[i] == 0 || buf[i] == byte('$') { buf[i]++ } } return buf } // Uint32 returns a lock free uint32 value. // //go:linkname Uint32 runtime.fastrand func Uint32() uint32 // Uint32N returns, as an uint32, a pseudo-random number in [0,n). func Uint32N(n uint32) uint32 { if n&(n-1) == 0 { // n is power of two, can mask return Uint32() & (n - 1) } return Uint32() % n } // Uint64N returns, as an uint64, a pseudo-random number in [0,n). func Uint64N(n uint64) uint64 { a := Uint32() b := Uint32() v := uint64(a)<<32 + uint64(b) if n&(n-1) == 0 { // n is power of two, can mask return v & (n - 1) } return v % n }