as.texinfo

基于4个mips核的noc设计

* Constants::                   Constants
@end menu

@node Preprocessing
@section Preprocessing

@cindex preprocessing
The @code{@value{AS}} internal preprocessor:
@itemize @bullet
@cindex whitespace, removed by preprocessor
@item
adjusts and removes extra whitespace.  It leaves one space or tab before
the keywords on a line, and turns any other whitespace on the line into
a single space.

@cindex comments, removed by preprocessor
@item
removes all comments, replacing them with a single space, or an
appropriate number of newlines.

@cindex constants, converted by preprocessor
@item
converts character constants into the appropriate numeric values.
@end itemize

It does not do macro processing, include file handling, or
anything else you may get from your C compiler's preprocessor.  You can
do include file processing with the @code{.include} directive
(@pxref{Include,,@code{.include}}).  You can use the @sc{gnu} C compiler driver
to get other ``CPP'' style preprocessing, by giving the input file a
@samp{.S} suffix.  @xref{Overall Options,, Options Controlling the Kind of
Output, gcc.info, Using GNU CC}.

Excess whitespace, comments, and character constants
cannot be used in the portions of the input text that are not
preprocessed.

@cindex turning preprocessing on and off
@cindex preprocessing, turning on and off
@kindex #NO_APP
@kindex #APP
If the first line of an input file is @code{#NO_APP} or if you use the
@samp{-f} option, whitespace and comments are not removed from the input file.
Within an input file, you can ask for whitespace and comment removal in
specific portions of the by putting a line that says @code{#APP} before the
text that may contain whitespace or comments, and putting a line that says
@code{#NO_APP} after this text.  This feature is mainly intend to support
@code{asm} statements in compilers whose output is otherwise free of comments
and whitespace.

@node Whitespace
@section Whitespace

@cindex whitespace
@dfn{Whitespace} is one or more blanks or tabs, in any order.
Whitespace is used to separate symbols, and to make programs neater for
people to read.  Unless within character constants
(@pxref{Characters,,Character Constants}), any whitespace means the same
as exactly one space.

@node Comments
@section Comments

@cindex comments
There are two ways of rendering comments to @code{@value{AS}}.  In both
cases the comment is equivalent to one space.

Anything from @samp{/*} through the next @samp{*/} is a comment.
This means you may not nest these comments.

@smallexample
/*
  The only way to include a newline ('\n') in a comment
  is to use this sort of comment.
*/

/* This sort of comment does not nest. */
@end smallexample

@cindex line comment character
Anything from the @dfn{line comment} character to the next newline
is considered a comment and is ignored.  The line comment character is
@ifset A29K
@samp{;} for the AMD 29K family;
@end ifset
@ifset ARC
@samp{;} on the ARC;
@end ifset
@ifset ARM
@samp{@@} on the ARM;
@end ifset
@ifset H8/300
@samp{;} for the H8/300 family;
@end ifset
@ifset H8/500
@samp{!} for the H8/500 family;
@end ifset
@ifset HPPA
@samp{;} for the HPPA;
@end ifset
@ifset I80386
@samp{#} on the i386 and x86-64;
@end ifset
@ifset I960
@samp{#} on the i960;
@end ifset
@ifset PJ
@samp{;} for picoJava;
@end ifset
@ifset SH
@samp{!} for the Hitachi SH;
@end ifset
@ifset SPARC
@samp{!} on the SPARC;
@end ifset
@ifset M32R
@samp{#} on the m32r;
@end ifset
@ifset M680X0
@samp{|} on the 680x0;
@end ifset
@ifset M68HC11
@samp{#} on the 68HC11 and 68HC12;
@end ifset
@ifset VAX
@samp{#} on the Vax;
@end ifset
@ifset Z8000
@samp{!} for the Z8000;
@end ifset
@ifset V850
@samp{#} on the V850;
@end ifset
see @ref{Machine Dependencies}.  @refill
@c FIXME What about m88k, i860?

@ifset GENERIC
On some machines there are two different line comment characters.  One
character only begins a comment if it is the first non-whitespace character on
a line, while the other always begins a comment.
@end ifset

@ifset V850
The V850 assembler also supports a double dash as starting a comment that
extends to the end of the line.

@samp{--};
@end ifset

@kindex #
@cindex lines starting with @code{#}
@cindex logical line numbers
To be compatible with past assemblers, lines that begin with @samp{#} have a
special interpretation.  Following the @samp{#} should be an absolute
expression (@pxref{Expressions}): the logical line number of the @emph{next}
line.  Then a string (@pxref{Strings,, Strings}) is allowed: if present it is a
new logical file name.  The rest of the line, if any, should be whitespace.

If the first non-whitespace characters on the line are not numeric,
the line is ignored.  (Just like a comment.)

@smallexample
                          # This is an ordinary comment.
# 42-6 "new_file_name"    # New logical file name
                          # This is logical line # 36.
@end smallexample
This feature is deprecated, and may disappear from future versions
of @code{@value{AS}}.

@node Symbol Intro
@section Symbols

@cindex characters used in symbols
@ifclear SPECIAL-SYMS
A @dfn{symbol} is one or more characters chosen from the set of all
letters (both upper and lower case), digits and the three characters
@samp{_.$}.
@end ifclear
@ifset SPECIAL-SYMS
@ifclear GENERIC
@ifset H8
A @dfn{symbol} is one or more characters chosen from the set of all
letters (both upper and lower case), digits and the three characters
@samp{._$}.  (Save that, on the H8/300 only, you may not use @samp{$} in
symbol names.)
@end ifset
@end ifclear
@end ifset
@ifset GENERIC
On most machines, you can also use @code{$} in symbol names; exceptions
are noted in @ref{Machine Dependencies}.
@end ifset
No symbol may begin with a digit.  Case is significant.
There is no length limit: all characters are significant.  Symbols are
delimited by characters not in that set, or by the beginning of a file
(since the source program must end with a newline, the end of a file is
not a possible symbol delimiter).  @xref{Symbols}.
@cindex length of symbols

@node Statements
@section Statements

@cindex statements, structure of
@cindex line separator character
@cindex statement separator character
@ifclear GENERIC
@ifclear abnormal-separator
A @dfn{statement} ends at a newline character (@samp{\n}) or at a
semicolon (@samp{;}).  The newline or semicolon is considered part of
the preceding statement.  Newlines and semicolons within character
constants are an exception: they do not end statements.
@end ifclear
@ifset abnormal-separator
@ifset A29K
A @dfn{statement} ends at a newline character (@samp{\n}) or an ``at''
sign (@samp{@@}).  The newline or at sign is considered part of the
preceding statement.  Newlines and at signs within character constants
are an exception: they do not end statements.
@end ifset
@ifset HPPA
A @dfn{statement} ends at a newline character (@samp{\n}) or an exclamation 
point (@samp{!}).  The newline or exclamation point is considered part of the
preceding statement.  Newlines and exclamation points within character
constants are an exception: they do not end statements.
@end ifset
@ifset H8
A @dfn{statement} ends at a newline character (@samp{\n}); or (for the
H8/300) a dollar sign (@samp{$}); or (for the
Hitachi-SH or the
H8/500) a semicolon
(@samp{;}).  The newline or separator character is considered part of
the preceding statement.  Newlines and separators within character
constants are an exception: they do not end statements.
@end ifset
@end ifset
@end ifclear
@ifset GENERIC
A @dfn{statement} ends at a newline character (@samp{\n}) or line
separator character.  (The line separator is usually @samp{;}, unless
this conflicts with the comment character; @pxref{Machine Dependencies}.)  The
newline or separator character is considered part of the preceding
statement.  Newlines and separators within character constants are an
exception: they do not end statements.
@end ifset

@cindex newline, required at file end
@cindex EOF, newline must precede
It is an error to end any statement with end-of-file:  the last
character of any input file should be a newline.@refill

An empty statement is allowed, and may include whitespace.  It is ignored.

@cindex instructions and directives
@cindex directives and instructions
@c "key symbol" is not used elsewhere in the document; seems pedantic to
@c @defn{} it in that case, as was done previously...  [e-mail],
@c 13feb91.
A statement begins with zero or more labels, optionally followed by a
key symbol which determines what kind of statement it is.  The key
symbol determines the syntax of the rest of the statement.  If the
symbol begins with a dot @samp{.} then the statement is an assembler
directive: typically valid for any computer.  If the symbol begins with
a letter the statement is an assembly language @dfn{instruction}: it
assembles into a machine language instruction.
@ifset GENERIC
Different versions of @code{@value{AS}} for different computers
recognize different instructions.  In fact, the same symbol may
represent a different instruction in a different computer's assembly
language.@refill
@end ifset

@cindex @code{:} (label)
@cindex label (@code{:})
A label is a symbol immediately followed by a colon (@code{:}).
Whitespace before a label or after a colon is permitted, but you may not
have whitespace between a label's symbol and its colon. @xref{Labels}.

@ifset HPPA
For HPPA targets, labels need not be immediately followed by a colon, but 
the definition of a label must begin in column zero.  This also implies that
only one label may be defined on each line.
@end ifset

@smallexample
label:     .directive    followed by something
another_label:           # This is an empty statement.
           instruction   operand_1, operand_2, @dots{}
@end smallexample

@node Constants
@section Constants

@cindex constants
A constant is a number, written so that its value is known by
inspection, without knowing any context.  Like this:
@smallexample
@group
.byte  74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
.ascii "Ring the bell\7"                  # A string constant.
.octa  0x123456789abcdef0123456789ABCDEF0 # A bignum.
.float 0f-314159265358979323846264338327\
95028841971.693993751E-40                 # - pi, a flonum.
@end group
@end smallexample

@menu
* Characters::                  Character Constants
* Numbers::                     Number Constants
@end menu

@node Characters
@subsection Character Constants

@cindex character constants
@cindex constants, character
There are two kinds of character constants.  A @dfn{character} stands
for one character in one byte and its value may be used in
numeric expressions.  String constants (properly called string
@emph{literals}) are potentially many bytes and their values may not be
used in arithmetic expressions.

@menu
* Strings::                     Strings
* Chars::                       Characters
@end menu

@node Strings
@subsubsection Strings

@cindex string constants
@cindex constants, string
A @dfn{string} is written between double-quotes.  It may contain
double-quotes or null characters.  The way to get special characters
into a string is to @dfn{escape} these characters: precede them with
a backslash @samp{\} character.  For example @samp{\\} represents
one backslash:  the first @code{\} is an escape which tells
@code{@value{AS}} to interpret the second character literally as a backslash
(which prevents @code{@value{AS}} from recognizing the second @code{\} as an
escape character).  The complete list of escapes follows.

@cindex escape codes, character
@cindex character escape codes
@table @kbd
@c      @item \a
@c      Mnemonic for ACKnowledge; for ASCII this is octal code 007.
@c
@cindex @code{\b} (backspace character)
@cindex backspace (@code{\b})
@item \b
Mnemonic for backspace; for ASCII this is octal code 010.

@c      @item \e
@c      Mnemonic for EOText; for ASCII this is octal code 004.
@c
@cindex @code{\f} (formfeed character)
@cindex formfeed (@code{\f})
@item \f
Mnemonic for FormFeed; for ASCII this is octal code 014.

@cindex @code{\n} (newline character)
@cindex newline (@code{\n})
@item \n
Mnemonic for newline; for ASCII this is octal code 012.

@c      @item \p
@c      Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}.
@c
@cindex @code{\r} (carriage return character)
@cindex carriage return (@code{\r})
@item \r
Mnemonic for carriage-Return; for ASCII this is octal code 015.

@c      @item \s
@c      Mnemonic for space; for ASCII this is octal code 040.  Included for compliance with
@c      other assemblers.
@c
@cindex @code{\t} (tab)
@cindex tab (@code{\t})
@item \t
Mnemonic for horizontal Tab; for ASCII this is octal code 011.

@c      @item \v
@c      Mnemonic for Vertical tab; for ASCII this is octal code 013.
@c      @item \x @var{digit} @var{digit} @var{digit}
@c      A hexadecimal character code.  The numeric code is 3 hexadecimal digits.
@c
@cindex @code{\@var{ddd}} (octal character code)
@cindex octal character code (@code{\@var