comment, called the preamble, is used as a header when compiling
the C parts of the package. For example:

	// #include <stdio.h>
	// #include <errno.h>
	import "C"

The preamble may contain any C code, including function and variable
declarations and definitions. These may then be referred to from Go
code as though they were defined in the package "C". All names
declared in the preamble may be used, even if they start with a

			t.Fatalf("ReadRune(%U) after UnreadRune got %U,%d not %U,%d (err=%s)", r, r2, nbytes, r, size, err)
		}
	}
}

func TestWriteInvalidRune(t *testing.T) {
	// Invalid runes, including negative ones, should be written as
	// utf8.RuneError.
	for _, r := range []rune{-1, utf8.MaxRune + 1} {
		var buf Buffer
		buf.WriteRune(r)
		check(t, fmt.Sprintf("TestWriteInvalidRune (%d)", r), &buf, "\uFFFD")

-->

## Introduction {#intro}

Go's emphasis on backwards compatibility is one of its key strengths.
There are, however, times when we cannot maintain complete compatibility.
If code depends on buggy (including insecure) behavior,
then fixing the bug will break that code.
New features can also have similar impacts:
enabling the HTTP/2 use by the HTTP client broke programs
connecting to servers with buggy HTTP/2 implementations.

	}
	b.lastRead = opInvalid
	if b.off > 0 {
		b.off--
	}
	return nil
}

// ReadBytes reads until the first occurrence of delim in the input,
// returning a slice containing the data up to and including the delimiter.
// If ReadBytes encounters an error before finding a delimiter,
// it returns the data read before the error and the error itself (often io.EOF).

//
// Tape archives (tar) are a file format for storing a sequence of files that
// can be read and written in a streaming manner.
// This package aims to cover most variations of the format,
// including those produced by GNU and BSD tar tools.
package tar

import (
	"errors"
	"fmt"
	"internal/godebug"
	"io/fs"
	"math"
	"path"
	"reflect"
	"strconv"
	"strings"
	"time"
)

	tok := in.Stack.Next()
	if tok != scanner.Ident {
		in.expectText("expected identifier after '#'")
	}
	if !in.enabled() {
		// Can only start including again if we are at #else or #endif but also
		// need to keep track of nested #if[n]defs.
		// We let #line through because it might affect errors.
		switch in.Stack.Text() {

	// Standard register names.
	for i := riscv.REG_X0; i <= riscv.REG_X31; i++ {
		// Disallow X3 in shared mode, as this will likely be used as the
		// GP register, which could result in problems in non-Go code,
		// including signal handlers.
		if shared && i == riscv.REG_GP {
			continue
		}
		if i == riscv.REG_TP || i == riscv.REG_G {
			continue
		}
		name := fmt.Sprintf("X%d", i-riscv.REG_X0)
		register[name] = int16(i)

	if len(p) > sr.max {
		p = p[0:sr.max]
	}
	return sr.buf.Read(p)
}

// genLine writes to buf a predictable but non-trivial line of text of length
// n, including the terminal newline and an occasional carriage return.
// If addNewline is false, the \r and \n are not emitted.
func genLine(buf *bytes.Buffer, lineNum, n int, addNewline bool) {
	buf.Reset()
	doCR := lineNum%5 == 0

		p.errorf("illegal register %s(%d)", name, r)
		return 0, false
	}
	return r, true
}

// register parses a full register reference where there is no symbol present (as in 4(R0) or R(10) but not sym(SB))
// including forms involving multiple registers such as R1:R2.
func (p *Parser) register(name string, prefix rune) (r1, r2 int16, scale int8, ok bool) {
	// R1 or R(1) R1:R2 R1,R2 R1+R2, or R1*scale.
	r1, ok = p.registerReference(name)

}

// ReadLine is a low-level line-reading primitive. Most callers should use
// [Reader.ReadBytes]('\n') or [Reader.ReadString]('\n') instead or use a [Scanner].
//
// ReadLine tries to return a single line, not including the end-of-line bytes.
// If the line was too long for the buffer then isPrefix is set and the
// beginning of the line is returned. The rest of the line will be returned