if _, err := io.ReadFull(r, buf[:4]); err != nil {
		return err
	}
	off := 0
	maybeSig := readBuf(buf[:4])
	if maybeSig.uint32() != dataDescriptorSignature {
		// No data descriptor signature. Keep these four
		// bytes.
		off += 4
	}
	if _, err := io.ReadFull(r, buf[off:12]); err != nil {
		return err
	}
	b := readBuf(buf[:12])
	if b.uint32() != f.CRC32 {

	if len(bmbuf) < maxSize {
		bmbuf = make([]byte, maxSize)
	}

	for _, n := range sizes {
		for _, off := range []int{0, 1, 4, 7} {
			buf1 := bmbuf[off : off+n]
			buf2Start := (len(bmbuf) / 2) + off
			buf2 := bmbuf[buf2Start : buf2Start+n]
			buf1[n-1] = 'x'
			buf2[n-1] = 'x'
			b.Run(fmt.Sprint(n, off), func(b *testing.B) {
				b.SetBytes(int64(n))
				for i := 0; i < b.N; i++ {
					eq := Equal(buf1, buf2)

	}
	buf := make([]byte, ss.Size())
	for off := int64(0); off < ss.Size(); off++ {
		for size := 1; size <= int(ss.Size()-off); size++ {
			readBuf := buf[:size]
			n, err := ss.ReadAt(readBuf, off)
			if off < ss.Size()-keep {
				if err != errDiscardedBytes {
					t.Errorf("off %d, size %d = %v, %v (%q); want errDiscardedBytes", off, size, n, err, readBuf[:n])
				}
				continue
			}

	return
}

// ReadAt implements the [io.ReaderAt] interface.
func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
	// cannot modify state - see io.ReaderAt
	if off < 0 {
		return 0, errors.New("bytes.Reader.ReadAt: negative offset")
	}
	if off >= int64(len(r.s)) {
		return 0, io.EOF
	}
	n = copy(b, r.s[off:])
	if n < len(b) {
		err = io.EOF
	}
	return
}

// TrimLeftFunc treats s as UTF-8-encoded bytes and returns a subslice of s by slicing off
// all leading UTF-8-encoded code points c that satisfy f(c).
func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
	i := indexFunc(s, f, false)
	if i == -1 {
		return nil
	}
	return s[i:]
}

// TrimRightFunc returns a subslice of s by slicing off all trailing
// UTF-8-encoded code points c that satisfy f(c).

			}
			count = int16((x & 31) << 7)
		}
	default:
		p.errorf("unexpected %s in register shift", tok.String())
	}
	if p.arch.Family == sys.ARM64 {
		off, err := arch.ARM64RegisterShift(r1, op, count)
		if err != nil {
			p.errorf(err.Error())
		}
		return off
	} else {
		return int64((r1 & 15) | op<<5 | count)
	}
}

// registerExtension parses a register with extension or arrangement.

	for _, growLen := range []int{0, 100, 1000, 10000, 100000} {
		for _, startLen := range []int{0, 100, 1000, 10000, 100000} {
			xBytes := Repeat(x, startLen)

			buf := NewBuffer(xBytes)
			// If we read, this affects buf.off, which is good to test.
			readBytes, _ := buf.Read(tmp)
			yBytes := Repeat(y, growLen)
			allocs := testing.AllocsPerRun(100, func() {
				buf.Grow(growLen)
				buf.Write(yBytes)
			})

		// don't spend all our time copying.
		copy(b.buf, b.buf[b.off:])
	} else if c > maxInt-c-n {
		panic(ErrTooLarge)
	} else {
		// Add b.off to account for b.buf[:b.off] being sliced off the front.
		b.buf = growSlice(b.buf[b.off:], b.off+n)
	}
	// Restore b.off and len(b.buf).
	b.off = 0
	b.buf = b.buf[:m+n]
	return m
}

			// structs are in system headers that cannot be corrected.
			continue
		}

		// Round off up to talign, assumed to be a power of 2.
		off = (off + talign - 1) &^ (talign - 1)

		if f.ByteOffset > off {
			fld, sizes = c.pad(fld, sizes, f.ByteOffset-off)
			off = f.ByteOffset
		}
		if f.ByteOffset < off {
			// Drop a packed field that we can't represent.
			continue
		}

		n := len(fld)

	}
	return strings.TrimRight(fmt.Sprintf("%s%d.%09d", sign, secs, nsecs), "0")
}

// parsePAXRecord parses the input PAX record string into a key-value pair.
// If parsing is successful, it will slice off the currently read record and
// return the remainder as r.
func parsePAXRecord(s string) (k, v, r string, err error) {
	// The size field ends at the first space.
	nStr, rest, ok := strings.Cut(s, " ")
	if !ok {