// without calling f.
func (o *Once) Do(f func()) {
	// Note: Here is an incorrect implementation of Do:
	//
	//	if o.done.CompareAndSwap(0, 1) {
	//		f()
	//	}
	//
	// Do guarantees that when it returns, f has finished.
	// This implementation would not implement that guarantee:
	// given two simultaneous calls, the winner of the cas would

	if labels == nil {
		return labelMap(nil)
	}
	return *labels
}

// labelMap is the representation of the label set held in the context type.
// This is an initial implementation, but it will be replaced with something
// that admits incremental immutable modification more efficiently.
type labelMap map[string]string

// String satisfies Stringer and returns key, value pairs in a consistent

//
// If dir is ".", Sub returns fsys unchanged.
// Otherwise, if fs implements [SubFS], Sub returns fsys.Sub(dir).
// Otherwise, Sub returns a new [FS] implementation sub that,
// in effect, implements sub.Open(name) as fsys.Open(path.Join(dir, name)).
// The implementation also translates calls to ReadDir, ReadFile, and Glob appropriately.
//
// Note that Sub(os.DirFS("/"), "prefix") is equivalent to os.DirFS("/prefix")

	restore(randState, randInc uint64)
}

// The functions in pcg implement a 32 bit PRNG with a 64 bit period: pcg xsh rr
// 64 32. See https://www.pcg-random.org/ for more information. This
// implementation is geared specifically towards the needs of fuzzing: Simple
// creation and use, no reproducibility, no concurrency safety, just the
// necessary methods, optimized for speed.

var globalInc atomic.Uint64 // PCG stream

}

// atomic_storePointer is the implementation of runtime/internal/UnsafePointer.Store
// (like StoreNoWB but with the write barrier).
//
//go:nosplit
//go:linkname atomic_storePointer internal/runtime/atomic.storePointer
func atomic_storePointer(ptr *unsafe.Pointer, new unsafe.Pointer) {
	atomicstorep(unsafe.Pointer(ptr), new)
}

// atomic_casPointer is the implementation of runtime/internal/UnsafePointer.CompareAndSwap

// ErrPersistEOF (above) reports that the remote side is closed.
var errClosed = errors.New("i/o operation on closed connection")

// ServerConn is an artifact of Go's early HTTP implementation.
// It is low-level, old, and unused by Go's current HTTP stack.
// We should have deleted it before Go 1.
//
// Deprecated: Use the Server in package [net/http] instead.
type ServerConn struct {

package sha1

import (
	"fmt"
	"io"
	"testing"
)

// Tests the fallback code path in case the optimized asm
// implementation cannot be used.
// See also TestBlockGeneric.
func TestGenericPath(t *testing.T) {
	if !useAsm {
		t.Skipf("assembly implementation unavailable")
	}
	useAsm = false
	defer func() { useAsm = true }()
	c := New()
	in := "ΑΒΓΔΕϜΖΗΘΙΚΛΜΝΞΟΠϺϘΡΣΤΥΦΧΨΩ"

package sha512

import (
	"fmt"
	"io"
	"testing"
)

// Tests the fallback code path in case the optimized asm
// implementation cannot be used.
// See also TestBlockGeneric.
func TestGenericPath(t *testing.T) {
	if !useAsm {
		t.Skipf("assembly implementation unavailable")
	}
	useAsm = false
	defer func() { useAsm = true }()
	c := New()
	in := "ΑΒΓΔΕϜΖΗΘΙΚΛΜΝΞΟΠϺϘΡΣΤΥΦΧΨΩ"

	// nested fields and methods than are shown here.) Clients
	// that use the compatibility shim T will compile with any
	// version of go, whether older or newer than go1.22, but only
	// the newer version will use the std.Real implementation.
	//
	// Now consider a reference to method M in new(T).F.M() in a
	// module that requires a minimum of go1.21. The analysis may
	// occur using a version of Go higher than 1.21, selecting the

// but also by other packages.
//
// See the [testing/fstest] package for support with testing
// implementations of file systems.
package fs

import (
	"internal/oserror"
	"time"
	"unicode/utf8"
)

// An FS provides access to a hierarchical file system.
//
// The FS interface is the minimum implementation required of the file system.
// A file system may implement additional interfaces,