// amd64/v1,amd64/v2:"BSRQ","LEAQ",-"CMOVQEQ"
	// amd64/v3: "LZCNTL",- "BSRL"
	// s390x:"FLOGR"
	// arm:"CLZ" arm64:"CLZW"
	// mips:"CLZ"
	// wasm:"I64Clz"
	// ppc64x:"CNTLZW"
	return bits.LeadingZeros32(n)
}

func LeadingZeros16(n uint16) int {
	// amd64/v1,amd64/v2:"BSRL","LEAL",-"CMOVQEQ"
	// amd64/v3: "LZCNTL",- "BSRL"
	// s390x:"FLOGR"
	// arm:"CLZ" arm64:"CLZ"
	// mips:"CLZ"

	"LODSB",
	"LODSL",
	"LODSQ",
	"LODSW",
	"LONG",
	"LOOP",
	"LOOPEQ",
	"LOOPNE",
	"LSLL",
	"LSLQ",
	"LSLW",
	"LSSL",
	"LSSQ",
	"LSSW",
	"LTR",
	"LZCNTL",
	"LZCNTQ",
	"LZCNTW",
	"MASKMOVOU",
	"MASKMOVQ",
	"MAXPD",
	"MAXPS",
	"MAXSD",
	"MAXSS",
	"MFENCE",
	"MINPD",
	"MINPS",
	"MINSD",
	"MINSS",
	"MONITOR",
	"MOVAPD",
	"MOVAPS",

		"pmovsxbw", "pmovsxbd", "pmovsxbq", "pmovsxwd", "pmovsxwq", "pmovsxdq",
		"pblendvb",
	},
	"fma":   {"vfmadd231sd"},
	"movbe": {"movbeqq", "movbeq", "movbell", "movbel", "movbe"},
	"lzcnt": {"lzcntq", "lzcntl", "lzcnt"},
}

// Test to use POPCNT instruction, if available
func TestPopCnt(t *testing.T) {
	for _, tt := range []struct {
		x    uint64
		want int
	}{
		{0b00001111, 4},

	ALLDT
	ALMSW
	ALOCK
	ALODSB
	ALODSL
	ALODSQ
	ALODSW
	ALONG
	ALOOP
	ALOOPEQ
	ALOOPNE
	ALSLL
	ALSLQ
	ALSLW
	ALSSL
	ALSSQ
	ALSSW
	ALTR
	ALZCNTL
	ALZCNTQ
	ALZCNTW
	AMASKMOVOU
	AMASKMOVQ
	AMAXPD
	AMAXPS
	AMAXSD
	AMAXSS
	AMFENCE
	AMINPD
	AMINPS
	AMINSD
	AMINSS
	AMONITOR
	AMOVAPD
	AMOVAPS
	AMOVB
	AMOVBEL

//sys	ioctlPtr(fd int, req int, arg unsafe.Pointer) (err error) = ioctl

// fcntl must never be called with cmd=F_DUP2FD because it doesn't work on AIX
// There is no way to create a custom fcntl and to keep //sys fcntl easily,
// Therefore, the programmer must call dup2 instead of fcntl in this case.

// FcntlInt performs a fcntl syscall on fd with the provided command and argument.

//sys	fcntl(fd int, cmd int, arg int) (n int, err error)
//sys	fcntlPtr(fd int, cmd int, arg unsafe.Pointer) (n int, err error) = SYS_FCNTL

// FcntlInt performs a fcntl syscall on fd with the provided command and argument.
func FcntlInt(fd uintptr, cmd, arg int) (int, error) {
	return fcntl(int(fd), cmd, arg)
}

// FcntlFlock performs a fcntl syscall for the F_GETLK, F_SETLK or F_SETLKW command.

// Not used on Darwin, but must be defined.
func exitThread(wait *atomic.Uint32) {
	throw("exitThread")
}

//go:nosplit
func setNonblock(fd int32) {
	flags, _ := fcntl(fd, _F_GETFL, 0)
	if flags != -1 {
		fcntl(fd, _F_SETFL, flags|_O_NONBLOCK)
	}
}

func issetugid() int32 {
	return libcCall(unsafe.Pointer(abi.FuncPCABI0(issetugid_trampoline)), nil)
}
func issetugid_trampoline()

var ioSync int64

func CloseOnExec(fd int) { fcntl(fd, F_SETFD, FD_CLOEXEC) }

func SetNonblock(fd int, nonblocking bool) (err error) {
	flag, err := fcntl(fd, F_GETFL, 0)
	if err != nil {
		return err
	}
	if (flag&O_NONBLOCK != 0) == nonblocking {
		return nil
	}
	if nonblocking {
		flag |= O_NONBLOCK
	} else {
		flag &= ^O_NONBLOCK
	}
	_, err = fcntl(fd, F_SETFL, flag)
	return err
}

		ALEAL, ALEAQ,
		AIMUL3W, AIMUL3L, AIMUL3Q,
		APEXTRB, APEXTRW, APEXTRD, APEXTRQ, AVPEXTRB, AVPEXTRW, AVPEXTRD, AVPEXTRQ, AEXTRACTPS,
		ABSFW, ABSFL, ABSFQ, ABSRW, ABSRL, ABSRQ, APOPCNTW, APOPCNTL, APOPCNTQ, ALZCNTW, ALZCNTL, ALZCNTQ,
		ASHLXL, ASHLXQ, ASHRXL, ASHRXQ, ASARXL, ASARXQ:
		// These instructions are pure writes to To. They don't use its old value.
		m &^= readTo
	case AXORL, AXORQ:

		r0, err := unix.Fcntl(fd, syscall.F_DUPFD_CLOEXEC, 0)
		if err == nil {
			return r0, "", nil
		}
		switch err {
		case syscall.EINVAL, syscall.ENOSYS:
			// Old kernel, or js/wasm (which returns
			// ENOSYS). Fall back to the portable way from
			// now on.
			dupCloexecUnsupported.Store(true)
		default:
			return -1, "fcntl", err
		}
	}
	return dupCloseOnExecOld(fd)
}