rand.go

// Copyright (c) 2020 Uber Technologies, Inc.
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// furnished to do so, subject to the following conditions:
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// Package unsafe contains operations that step around the type safety of Go programs.
package unsafe

import (
	_ "unsafe" // needed for go:linkname hack
)

//go:linkname fastrand runtime.fastrand
func fastrand() uint32

// Fastrandn returns a uint32 in range of 0..n, like rand() % n, but faster not as precise,
// https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
func Fastrandn(n uint32) uint32 {
	// This is similar to fastrand() % n, but faster.
	return uint32(uint64(fastrand()) * uint64(n) >> 32)
}