Go1.22 add frist v2 lib, math/rand/v2 more fast and more Standard

The inaugural v2 version of the standard library in Go, hails from the esteemed math/rand/v2 repository. It is set to make its grand debut with the official release of Go1.22, poised to serve as a reliable and production-ready resource.

Reasons

1. The original math/rand library in the standard package had numerous deficiencies and areas for improvement. These included outdated generators, slow algorithms (performance), and unfortunate conflicts with crypto/rand.Read, among other issues.
2. There is a plan in place to upgrade the v2 versions of standard libraries. Starting with math allows for the accumulation of experience and resolving tooling ecosystem challenges (such as support from tools like gopls and goimports for v2 packages). Subsequent iterations can then address higher-risk packages, like sync/v2 or encoding/json/v2.
3. Go1 requires compatibility guarantees, making it impractical to directly modify the original library. The issues with math/rand are also more prominent and evident.

change list

• Removed Rand.Read and the top-level Read function.
• Removed Source.Seed, Rand.Seed, and the top-level Seed function (meaning that top-level functions like Int will always use random seeding).
• Removed Source64, as Source now provides the Uint64 method, making the original methods unnecessary.
• Utilized a more direct implementation for Float32 and Float64. For example, in the case of Float64, the original implementation used float64(r.Int63()) / (1<<63). However, this had a problem of occasionally rounding to 1.0, while Float64 should never round. The improvement involves changing it to float64(r.Int63n(1<<53)) / (1<<53), which avoids the rounding issue.
• Implemented Rand.Perm using Rand.Shuffle. This improves efficiency and ensures only one implementation.
• Renamed Int31, Int31n, Int63, and Int64n to Int32, Int32n, Int64, and Int64n, respectively. These names were unnecessary and confusing.
• Added Uint32, Uint32n, Uint64, Uint64n, Uint, and Uintn as top-level functions and methods on Rand.
• Utilized Lemire’s algorithm in Intn, Uintn, Int32n, Uint32n, Int64n, and Uint64n, resulting in improved performance.
• Introduced a new implementation of Source called PCG-DXSM, including related APIs like NewPCG.
• Removed the Mitchell & Reeds LFSR generator and NewSource.

example

Read & Seed

The functions Read and Seed have been removed. It is recommended to use crypto/rand's Read function instead.

import ( 
  "crypto/rand" 
  "fmt" 
 ) 
 ​ 
 func main() { 
  b := make([]byte, 3) 
  _, err := rand.Read(b) 
  if err != nil { 
   panic(err) 
  } 
  fmt.Printf("hxzhouh: %v\n", b) 
 }

output：

hxzhouh: [48 71 122]

For the Seed function, it is advised to call New(NewSource(seed)) in order to reinitialize the random number generator.

internal

The functions N, IntN, and UintN now utilize a novel implementation algorithm. Interested individuals are encouraged to allocate extra time to examine it in detail:A fast alternative to the modulo reduction

The functions Intn, Int31, Int31n, Int63, and Int64n have been renamed as follows: IntN, Int32, Int32N, Int64, and Int64N, respectively.

Additionally, new functions Uint32, Uint32N, Uint64, Uint64N, Uint, and UintN have been introduced to generate random unsigned integers. They have also been added as corresponding functions within the Rand structure.

The newly added function N generates random numbers of arbitrary integer types. This function is implemented using generics, and the following integer types are its type parameters:

• int
• int8
• int16
• int32
• int64

Summary:

Today, we have shared and further described the new math/rand/v2 library, highlighting key changes including performance optimization (algorithm rewrite), standardization, and additions of new random generators.

Given the substantial amount of information covered, we have selected and presented only the aspects that are essential for understanding and using the library. However, for those who are interested in delving deeper, it is recommended to refer to the full documentation ofhttps://pkg.go.dev/math/rand/v2@master

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