<p>
The built-in functions <code>len</code> and <code>cap</code> take arguments
of various types and return a result of type <code>int</code>.
The implementation guarantees that the result always fits into an <code>int</code>.
</p>

<pre class="grammar">
Call      Argument type    Result

len(s)    string type      string length in bytes
          [n]T, *[n]T      array length (== n)

	if testing.Short() {
		t.Skip("slow test; skipping")
	}
	t.Parallel()
	// Test a zip file with uncompressed size 0xFFFFFFFF.
	// That's the magic marker for a 64-bit file, so even though
	// it fits in a 32-bit field we must use the 64-bit field.
	// Go 1.5 and earlier got this wrong,
	// writing an invalid zip file.
	const size = 1<<32 - 1 - int64(len("END\n")) // before the "END\n" part
	buf := testZip64(t, size)

</pre>

<p>
If the capacity of <code>s</code> is not large enough to fit the additional
values, <code>append</code> <a href="#Allocation">allocates</a> a new, sufficiently large underlying
array that fits both the existing slice elements and the additional values.
Otherwise, <code>append</code> re-uses the underlying array.
</p>

<pre>
s0 := []int{0, 0}

	// Add leading zeros, but leave room for a NUL.
	if n := len(b) - len(s) - 1; n > 0 {
		s = strings.Repeat("0", n) + s
	}
	f.formatString(b, s)
}

// fitsInOctal reports whether the integer x fits in a field n-bytes long
// using octal encoding with the appropriate NUL terminator.
func fitsInOctal(n int, x int64) bool {
	octBits := uint(n-1) * 3
	return x >= 0 && (n >= 22 || x < 1<<octBits)
}

	copy(b2, b)
	return b2[:len(b)]
}

// WriteTo writes data to w until the buffer is drained or an error occurs.
// The return value n is the number of bytes written; it always fits into an
// int, but it is int64 to match the io.WriterTo interface. Any error
// encountered during the write is also returned.
func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
	b.lastRead = opInvalid

	MOVW	$0, (R1)  // 3f0000b9
	MOVWU	$0, (R1)  // 3f0000b9
	MOVH	$0, (R1)  // 3f000079
	MOVHU	$0, (R1)  // 3f000079
	MOVB	$0, (R1)  // 3f000039
	MOVBU	$0, (R1)  // 3f000039

// small offset fits into instructions
	MOVB	R1, 1(R2) // 41040039
	MOVH	R1, 1(R2) // 41100078
	MOVH	R1, 2(R2) // 41040079
	MOVW	R1, 1(R2) // 411000b8
	MOVW	R1, 4(R2) // 410400b9
	MOVD	R1, 1(R2) // 411000f8