util.go

package xsync

import (
	"math/bits"
	"runtime"
	_ "unsafe"
)

// test-only assert()-like flag
var assertionsEnabled = false

const (
	// cacheLineSize is used in paddings to prevent false sharing;
	// 64B are used instead of 128B as a compromise between
	// memory footprint and performance; 128B usage may give ~30%
	// improvement on NUMA machines.
	cacheLineSize = 64
)

// nextPowOf2 computes the next highest power of 2 of 32-bit v.
// Source: https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
func nextPowOf2(v uint32) uint32 {
	if v == 0 {
		return 1
	}
	v--
	v |= v >> 1
	v |= v >> 2
	v |= v >> 4
	v |= v >> 8
	v |= v >> 16
	v++
	return v
}

func parallelism() uint32 {
	maxProcs := uint32(runtime.GOMAXPROCS(0))
	numCores := uint32(runtime.NumCPU())
	if maxProcs < numCores {
		return maxProcs
	}
	return numCores
}

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

func broadcast(b uint8) uint64 {
	return 0x101010101010101 * uint64(b)
}

func firstMarkedByteIndex(w uint64) int {
	return bits.TrailingZeros64(w) >> 3
}

// SWAR byte search: may produce false positives, e.g. for 0x0100,
// so make sure to double-check bytes found by this function.
func markZeroBytes(w uint64) uint64 {
	return ((w - 0x0101010101010101) & (^w) & 0x8080808080808080)
}

func setByte(w uint64, b uint8, idx int) uint64 {
	shift := idx << 3
	return (w &^ (0xff << shift)) | (uint64(b) << shift)
}