github.com/whtcorpsinc/milevadb-prod@v0.0.0-20211104133533-f57f4be3b597/soliton/fastrand/random.go (about)

     1  // Copyright 2020 WHTCORPS INC, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package fastrand
    15  
    16  import (
    17  	_ "unsafe" // required by go:linkname
    18  )
    19  
    20  // Buf generates a random string using ASCII characters but avoid separator character.
    21  // See https://github.com/allegrosql/allegrosql-server/blob/5.7/mysys_ssl/crypt_genhash_impl.cc#L435
    22  func Buf(size int) []byte {
    23  	buf := make([]byte, size)
    24  	for i := 0; i < size; i++ {
    25  		buf[i] = byte(Uint32N(127))
    26  		if buf[i] == 0 || buf[i] == byte('$') {
    27  			buf[i]++
    28  		}
    29  	}
    30  	return buf
    31  }
    32  
    33  // Uint32 returns a dagger free uint32 value.
    34  //go:linkname Uint32 runtime.fastrand
    35  func Uint32() uint32
    36  
    37  // Uint32N returns, as an uint32, a pseudo-random number in [0,n).
    38  func Uint32N(n uint32) uint32 {
    39  	if n&(n-1) == 0 { // n is power of two, can mask
    40  		return Uint32() & (n - 1)
    41  	}
    42  	return Uint32() % n
    43  }
    44  
    45  // Uint64N returns, as an uint64, a pseudo-random number in [0,n).
    46  func Uint64N(n uint64) uint64 {
    47  	a := Uint32()
    48  	b := Uint32()
    49  	v := uint64(a)<<32 + uint64(b)
    50  	if n&(n-1) == 0 { // n is power of two, can mask
    51  		return v & (n - 1)
    52  	}
    53  	return v % n
    54  }