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ΓòÉΓòÉΓòÉ 1. Title page ΓòÉΓòÉΓòÉ

                                  DRAFT EDITION

                         GASP, an assembly preprocessor

                               for GASP version 1

                                   March 1994

                                   Roland Pesch

Copyright (C) 1994 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual
provided the copyright notice and this permission notice are preserved on all
copies.

Permission is granted to copy and distribute modified versions of this manual
under the conditions for verbatim copying, provided also that the entire
resulting derived work is distributed under the terms of a permission notice
identical to this one.

Permission is granted to copy and distribute translations of this manual into
another language, under the above conditions for modified versions.


ΓòÉΓòÉΓòÉ 2. Top node: "GASP" ΓòÉΓòÉΓòÉ

GASP is a preprocessor for assembly programs.

This file describes version 1 of GASP.

Steve Chamberlain wrote GASP; Roland Pesch wrote this manual.

 Overview                                What is GASP?
 Invoking GASP                           Command line options.
 Commands                                Preprocessor commands.
 Index                                   Index.


ΓòÉΓòÉΓòÉ 3. What is GASP? ΓòÉΓòÉΓòÉ

The primary purpose of the gnu assembler is to assemble the output of other
programs---notably compilers.  When you have to hand-code specialized routines
in assembly, that means the gnu assembler is an unfriendly processor: it has no
directives for macros, conditionals, or many other conveniences that you might
expect.

In some cases you can simply use the C preprocessor, or a generalized
preprocessor like m4; but this can be awkward, since none of these things are
designed with assembly in mind.

gasp fills this need.  It is expressly designed to provide the facilities you
need with hand-coded assembly code.  Implementing it as a preprocessor, rather
than part of the assembler, allows the maximum flexibility: you can use it with
hand-coded assembly, without paying a penalty of added complexity in the
assembler you use for compiler output.

Here is a small example to give the flavor of gasp.  This input to gasp

        .MACRO  saveregs from=8 to=14
count   .ASSIGNA \from
        ! save r\from..r\to
        .AWHILE  \&count LE \to
        mov     r\&count,@-sp
count   .ASSIGNA  \&count + 1
        .AENDW
        .ENDM

        saveregs from=12

bar:    mov     #H'dead+10,r0
foo     .SDATAC "hello"<10>
        .END

generates this assembly program:

        ! save r12..r14
        mov     r12,@-sp
        mov     r13,@-sp
        mov     r14,@-sp

bar:    mov     #57005+10,r0
foo:    .byte   6,104,101,108,108,111,10


ΓòÉΓòÉΓòÉ 4. Command Line Options ΓòÉΓòÉΓòÉ

The simplest way to use gasp is to run it as a filter and assemble its output.
In Unix and its ilk, you can do this, for example:

$ gasp prog.asm | as -o prog.o

Naturally, there are also a few command-line options to allow you to request
variations on this basic theme.  Here is the full set of possibilities for the
gasp command line.

gasp  [ -a | --alternate ]
      [ -c char | --commentchar char ]
      [ -d | --debug ]  [ -h | --help ]
      [ -o outfile | --output outfile ]
      [ -p | --print ]  [ -s | --copysource ]
      [ -u | --unreasonable ]  [ -v | --version ]
      infile ...
infile ... The input file names.  You must specify at least one input file; if
you specify more, gasp preprocesses them all, concatenating the output in the
order you list the infile arguments.

Mark the end of each input file with the preprocessor command .END.  See
Miscellaneous commands. -a --alternate Use alternative macro syntax. See
Alternate macro syntax, for a discussion of how this syntax differs from the
default gasp syntax. -c 'char' --commentchar 'char' Use char as the comment
character.  The default comment character is `!'.  For example, to use a
semicolon as the comment character, specify `-c ';'' on the gasp command line.
Since assembler command characters often have special significance to command
shells, it is a good idea to quote or escape char when you specify a comment
character.

For the sake of simplicity, all examples in this manual use the default comment
character `!'. -d --debug Show debugging statistics.  In this version of gasp,
this option produces statistics about the string buffers that gasp allocates
internally.  For each defined buffersize s, gasp shows the number of strings n
that it allocated, with a line like this:

strings size s : n

gasp displays these statistics on the standard error stream, when done
preprocessing. -h --help Display a summary of the gasp command line options. -o
outfile --output outfile Write the output in a file called outfile.  If you do
not use the `-o' option, gasp writes its output on the standard output stream.
-p --print Print line numbers.  gasp obeys this option only if you also specify
`-s' to copy source lines to its output.  With `-s -p', gasp displays the line
number of each source line copied (immediately after the comment character at
the beginning of the line). -s --copysource Copy the source lines to the output
file.  Use this option to see the effect of each preprocessor line on the gasp
output. gasp places a comment character (`!' by default) at the beginning of
each source line it copies, so that you can use this option and still assemble
the result. -u --unreasonable Bypass ``unreasonable expansion'' limit.  Since
you can define gasp macros inside other macro definitions, the preprocessor
normally includes a sanity check.  If your program requires more than 1,000
nested expansions, gasp normally exits with an error message.  Use this option
to turn off this check, allowing unlimited nested expansions. -v --version
Display the gasp version number.


ΓòÉΓòÉΓòÉ 5. Preprocessor Commands ΓòÉΓòÉΓòÉ

gasp commands have a straightforward syntax that fits in well with assembly
conventions.  In general, a command extends for a line, and may have up to
three fields: an optional label, the command itself, and optional arguments to
the command.  You can write commands in upper or lower case, though this manual
shows them in upper case. See Details of the GASP syntax, for more information.

 Conditionals
 Loops
 Variables
 Macros
 Data
 Listings
 Other Commands
 Syntax Details
 Alternate


ΓòÉΓòÉΓòÉ 5.1. Conditional assembly ΓòÉΓòÉΓòÉ

The conditional-assembly directives allow you to include or exclude portions of
an assembly depending on how a pair of expressions, or a pair of strings,
compare.

The overall structure of conditionals is familiar from many other contexts.
.AIF marks the start of a conditional, and precedes assembly for the case when
the condition is true.  An optional .AELSE precedes assembly for the converse
case, and an .AENDI marks the end of the condition.

You may nest conditionals up to a depth of 100; gasp rejects nesting beyond
that, because it may indicate a bug in your macro structure.

Conditionals are primarily useful inside macro definitions, where you often
need different effects depending on argument values. See Defining your own
directives, for details about defining macros. .AIF expra cmp exprb .AIF "stra"
cmp "strb"

The governing condition goes on the same line as the .AIF preprocessor command.
You may compare either two strings, or two expressions.

When you compare strings, only two conditional cmp comparison operators are
available: `EQ' (true if stra and strb are identical), and `NE' (the converse).

When you compare two expressions, both expressions must be absolute (see
Arithmetic expressions in GASP).  You can use these cmp comparison operators
with expressions: EQ Are expra and exprb equal?  (For strings, are stra and
strb identical?) NE Are expra and exprb different?  (For strings, are stra and
strb different? LT Is expra less than exprb?  (Not allowed for strings.) LE Is
expra less than or equal to exprb?  (Not allowed for strings.) GT Is expra
greater than exprb?  (Not allowed for strings.) GE Is expra greater than or
equal to exprb?  (Not allowed for strings.) .AELSE Marks the start of assembly
           code to be included if the condition fails. Optional, and only
           allowed within a conditional (between .AIF and .AENDI). .AENDI Marks
           the end of a conditional assembly.


ΓòÉΓòÉΓòÉ 5.2. Repetitive sections of assembly ΓòÉΓòÉΓòÉ

Two preprocessor directives allow you to repeatedly issue copies of the same
block of assembly code. .AREPEAT aexp .AENDR If you simply need to repeat the
same block of assembly over and over a fixed number of times, sandwich one
instance of the repeated block between .AREPEAT and .AENDR.  Specify the number
of copies as aexp (which must be an absolute expression).  For example, this
repeats two assembly statements three times in succession:

        .AREPEAT        3
        rotcl   r2
        div1    r0,r1
        .AENDR
.AWHILE expra cmp exprb .AENDW .AWHILE stra cmp strb .AENDW To repeat a block
of assembly depending on a conditional test, rather than repeating it for a
specific number of times, use .AWHILE. .AENDW marks the end of the repeated
block.  The conditional comparison works exactly the same way as for .AIF, with
the same comparison operators (see Conditional assembly).

Since the terms of the comparison must be absolute expression, .AWHILE is
primarily useful within macros. See Defining your own directives.

 You can use the .EXITM preprocessor directive to break out of loops early (as
 well as to break out of macros). See Defining your own directives.


ΓòÉΓòÉΓòÉ 5.3. Preprocessor variables ΓòÉΓòÉΓòÉ

You can use variables in gasp to represent strings, registers, or the results
of expressions.

You must distinguish two kinds of variables:

   1. Variables defined with .EQU or .ASSIGN.  To evaluate this kind of
      variable in your assembly output, simply mention its name.  For example,
      these two lines define and use a variable `eg':

            eg     .EQU   FLIP-64
                   ...
                   mov.l  eg,r0

      Do not use this kind of variable in conditional expressions or while
      loops; gasp only evaluates these variables when writing assembly output.

   2. Variables for use during preprocessing.  You can define these with
      .ASSIGNC or .ASSIGNA.  To evaluate this kind of variable, write `\&'
      before the variable name; for example,

            opcit  .ASSIGNA  47
                   ...
                   .AWHILE  \&opcit GT 0
                   ...
                   .AENDW

      gasp treats macro arguments almost the same way, but to evaluate them you
      use the prefix `\' rather than `\&'. See Defining your own directives.
 pvar .EQU expr Assign preprocessor variable pvar the value of the expression
 expr.  There are no restrictions on redefinition; use `.EQU' with the same
 pvar as often as you find it convenient. pvar .ASSIGN expr Almost the same as
 .EQU, save that you may not redefine pvar using .ASSIGN once it has a value.
 pvar .ASSIGNA aexpr Define a variable with a numeric value, for use during
 preprocessing. aexpr must be an absolute expression.  You can redefine
 variables with .ASSIGNA at any time. pvar .ASSIGNC "str" Define a variable
 with a string value, for use during preprocessing. You can redefine variables
 with .ASSIGNC at any time. pvar .REG (register) Use .REG to define a variable
 that represents a register.  In particular, register is not evaluated as an
 expression. You may use .REG at will to redefine register variables.

 All these directives accept the variable name in the ``label'' position, that
 is at the left margin.  You may specify a colon after the variable name if you
 wish; the first example above could have started `eg:' with the same effect.


ΓòÉΓòÉΓòÉ 5.4. Defining your own directives ΓòÉΓòÉΓòÉ

The commands .MACRO and .ENDM allow you to define macros that generate assembly
output.  You can use these macros with a syntax similar to built-in gasp or
assembler directives.  For example, this definition specifies a macro SUM that
adds together a range of consecutive registers:

        .MACRO  SUM FROM=0, TO=9
        ! \FROM \TO
        mov     r\FROM,r10
COUNT   .ASSIGNA        \FROM+1
        .AWHILE \&COUNT LE \TO
        add     r\&COUNT,r10
COUNT   .ASSIGNA        \&COUNT+1
        .AENDW
        .ENDM

With that definition, `SUM 0,5' generates this assembly output:

        ! 0 5
        mov     r0,r10
        add     r1,r10
        add     r2,r10
        add     r3,r10
        add     r4,r10
        add     r5,r10
.MACRO macname .MACRO macname macargs ... Begin the definition of a macro
called macname.  If your macro definition requires arguments, specify their
names after the macro name, separated by commas or spaces.  You can supply a
default value for any macro argument by following the name with `=deflt'.  For
example, these are all valid .MACRO statements:

           .MACRO COMM
                          Begin the definition of a macro called COMM, which
                          takes no arguments.

           .MACRO PLUS1 P, P1
           .MACRO PLUS1 P P1
                          Either statement begins the definition of a macro
                          called PLUS1, which takes two arguments; within the
                          macro definition, write `\P' or `\P1' to evaluate the
                          arguments.

           .MACRO RESERVE_STR P1=0 P2
                          Begin the definition of a macro called RESERVE_STR,
                          with two arguments.  The first argument has a default
                          value, but not the second. After the definition is
                          complete, you can call the macro either as
                          `RESERVE_STR a,b' (with `\P1' evaluating to a and
                          `\P2' evaluating to b), or as `RESERVE_STR ,b' (with
                          `\P1' evaluating as the default, in this case `0',
                          and `\P2' evaluating to b).

           When you call a macro, you can specify the argument values either by
           position, or by keyword.  For example, `SUM 9,17' is equivalent to
           `SUM TO=17, FROM=9'.  Macro arguments are preprocessor variables
           similar to the variables you define with `.ASSIGNA' or `.ASSIGNC';
           in particular, you can use them in conditionals or for loop control.
           (The only difference is the prefix you write to evaluate the
           variable: for a macro argument, write `\argname', but for a
           preprocessor variable, write `\&varname'.) name .MACRO name .MACRO (
           macargs ... ) An alternative form of introducing a macro definition:
           specify the macro name in the label position, and the arguments (if
           any) between parentheses after the name.  Defaulting rules and usage
           work the same way as for the other macro definition syntax. .ENDM
           Mark the end of a macro definition. .EXITM Exit early from the
           current macro definition, .AREPEAT loop, or .AWHILE loop. \@ gasp
           maintains a counter of how many macros it has executed in this
           pseudo-variable; you can copy that number to your output with `\@',
           but only within a macro definition. LOCAL name [ , ... ] Warning:
           LOCAL is only available if you select ``alternate macro syntax''
           with `-a' or `--alternate'. See Alternate macro syntax.

           Generate a string replacement for each of the name arguments, and
           replace any instances of name in each macro expansion.  The
           replacement string is unique in the assembly, and different for each
           separate macro expansion.  LOCAL allows you to write macros that
           define symbols, without fear of conflict between separate macro
           expansions.


ΓòÉΓòÉΓòÉ 5.5. Data output ΓòÉΓòÉΓòÉ

In assembly code, you often need to specify working areas of memory; depending
on the application, you may want to initialize such memory or not.  gasp
provides preprocessor directives to help you avoid repetitive coding for both
purposes.

You can use labels as usual to mark the data areas.

 Initialized
 Uninitialized


ΓòÉΓòÉΓòÉ 5.5.1. Initialized data ΓòÉΓòÉΓòÉ

These are the gasp directives for initialized data, and the standard gnu
assembler directives they expand to: .DATA expr, expr, ... .DATA.B expr, expr,
... .DATA.W expr, expr, ... .DATA.L expr, expr, ... Evaluate arithmetic
expressions expr, and emit the corresponding as directive (labelled with lab).
The unqualified .DATA emits `.long'; .DATA.B emits `.byte'; .DATA.W emits
`.short'; and .DATA.L emits `.long'.

For example, `foo .DATA 1,2,3' emits `foo: .long 1,2,3'. .DATAB repeat, expr
.DATAB.B repeat, expr .DATAB.W repeat, expr .DATAB.L repeat, expr Make as emit
repeat copies of the value of the expression expr (using the as directive
.fill). `.DATAB.B' repeats one-byte values; `.DATAB.W' repeats two-byte values;
and `.DATAB.L' repeats four-byte values. `.DATAB' without a suffix repeats
four-byte values, just like `.DATAB.L'.

repeat must be an absolute expression with a positive value. .SDATA "str" ...
String data.  Emits a concatenation of bytes, precisely as you specify them (in
particular, nothing is added to mark the end of the string).  See String and
numeric constants, for details about how to write strings.  .SDATA concatenates
multiple arguments, making it easy to switch between string representations.
You can use commas to separate the individual arguments for clarity, if you
choose. .SDATAB repeat, "str" ... Repeated string data.  The first argument
specifies how many copies of the string to emit; the remaining arguments
specify the string, in the same way as the arguments to .SDATA. .SDATAZ "str"
... Zero-terminated string data.  Just like .SDATA, except that .SDATAZ writes
a zero byte at the end of the string. .SDATAC "str" ... Count-prefixed string
data.  Just like .SDATA, except that gasp precedes the string with a leading
one-byte count.  For example, `.SDATAC "HI"' generates `.byte 2,72,73'.  Since
the count field is only one byte, you can only use .SDATAC for strings less
than 256 bytes in length.


ΓòÉΓòÉΓòÉ 5.5.2. Uninitialized data ΓòÉΓòÉΓòÉ

Use the .RES, .SRES, .SRESC, and .SRESZ directives to reserve memory and leave
it uninitialized.  gasp resolves these directives to appropriate calls of the
gnu as .space directive. .RES count .RES.B count .RES.W count .RES.L count
Reserve room for count uninitialized elements of data.  The suffix specifies
the size of each element: .RES.B reserves count bytes, .RES.W reserves count
pairs of bytes, and .RES.L reserves count quartets.  .RES without a suffix is
equivalent to .RES.L. .SRES count .SRES.B count .SRES.W count .SRES.L count
.SRES is a synonym for `.RES'. .SRESC count .SRESC.B count .SRESC.W count
.SRESC.L count Like .SRES, but reserves space for count+1 elements. .SRESZ
count .SRESZ.B count .SRESZ.W count .SRESZ.L count Like .SRES, but reserves
space for count+1 elements.


ΓòÉΓòÉΓòÉ 5.6. Assembly listing control ΓòÉΓòÉΓòÉ

The gasp listing-control directives map straightforwardly to related gnu as
directives. .PRINT LIST .PRINT NOLIST Print control.  This directive emits the
gnu as directive .list or .nolist, according to its argument. See .list, for
details on how these directives interact. .FORM LIN=ln .FORM COL=cols .FORM
LIN=ln COL=cols Specify the page size for assembly listings: ln represents the
number of lines, and cols the number of columns.  You may specify either page
dimension independently, or both together.  If you do not specify the number of
lines, gasp assumes 60 lines; if you do not specify the number of columns, gasp
assumes 132 columns. (Any values you may have specified in previous instances
of .FORM do not carry over as defaults.)  Emits the .psize assembler directive.
.HEADING string Specify string as the title of your assembly listings.  Emits
`.title "string"'. .PAGE Force a new page in assembly listings.  Emits
`.eject'.


ΓòÉΓòÉΓòÉ 5.7. Miscellaneous commands ΓòÉΓòÉΓòÉ

.ALTERNATE Use the alternate macro syntax henceforth in the assembly. See
Alternate macro syntax. .ORG This command is recognized, but not yet
implemented.  gasp generates an error message for programs that use .ORG.
.RADIX s gasp understands numbers in any of base two, eight, ten, or sixteen.
You can encode the base explicitly in any numeric constant (see String and
numeric constants).  If you write numbers without an explicit indication of the
base, the most recent `.RADIX s' command determines how they are interpreted. s
is a single letter, one of the following:

           .RADIX B
                          Base 2.

           .RADIX Q
                          Base 8.

           .RADIX D
                          Base 10.  This is the original default radix.

           .RADIX H
                          Base 16.

           You may specify the argument s in lower case (any of `bqdh') with
           the same effects. .EXPORT name .GLOBAL name Declare name global
           (emits `.global name').  The two directives are synonymous. .PROGRAM
           No effect: gasp accepts this directive, and silently ignores it.
           .END Mark end of each preprocessor file.  gasp issues a warning if
           it reaches end of file without seeing this command. .INCLUDE "str"
           Preprocess the file named by str, as if its contents appeared where
           the .INCLUDE directive does.  gasp imposes a maximum limit of 30
           stacked include files, as a sanity check. .ALIGN size Evaluate the
           absolute expression size, and emit the assembly instruction `.align
           size' using the result.


ΓòÉΓòÉΓòÉ 5.8. Details of the GASP syntax ΓòÉΓòÉΓòÉ

Since gasp is meant to work with assembly code, its statement syntax has no
surprises for the assembly programmer.

Whitespace (blanks or tabs; not newline) is partially significant, in that it
delimits up to three fields in a line.  The amount of whitespace does not
matter; you may line up fields in separate lines if you wish, but gasp does not
require that.

The first field, an optional label, must be flush left in a line (with no
leading whitespace) if it appears at all.  You may use a colon after the label
if you wish; gasp neither requires the colon nor objects to it (but will not
include it as part of the label name).

The second field, which must appear after some whitespace, contains a gasp or
assembly directive.

Any further fields on a line are arguments to the directive; you can separate
them from one another using either commas or whitespace.

 Markers
 Constants
 Symbols
 Expressions
 String Builtins


ΓòÉΓòÉΓòÉ 5.8.1. Special syntactic markers ΓòÉΓòÉΓòÉ

gasp recognizes a few special markers: to delimit comments, to continue a
statement on the next line, to separate symbols from other characters, and to
copy text to the output literally.  (One other special marker, `\@', works only
within macro definitions; see Defining your own directives.)

The trailing part of any gasp source line may be a comment. A comment begins
with the first unquoted comment character (`!' by default), or an escaped or
doubled comment character (`\!' or `!!' by default), and extends to the end of
a line.  You can specify what comment character to use with the `-c' option
(see Command Line Options).  The two kinds of comment markers lead to slightly
different treatment:

 !
           A single, un-escaped comment character generates an assembly comment
           in the gasp output.  gasp evaluates any preprocessor variables
           (macro arguments, or variables defined with .ASSIGNA or .ASSIGNC)
           present.  For example, a macro that begins like this

                              .MACRO  SUM FROM=0, TO=9
                              ! \FROM \TO

           issues as the first line of output a comment that records the values
           you used to call the macro.

 \!
 !!
           Either an escaped comment character, or a double comment character,
           marks a gasp source comment.  gasp does not copy such comments to
           the assembly output.

 To continue a statement on the next line of the file, begin the second line
 with the character `+'.

 Occasionally you may want to prevent gasp from preprocessing some particular
 bit of text.  To copy literally from the gasp source to its output, place `\('
 before the string to copy, and `)' at the end.  For example, write `\(\!)' if
 you need the characters `\!' in your assembly output.

 To separate a preprocessor variable from text to appear immediately after its
 value, write a single quote (').  For example, `.SDATA "\P'1"' writes a string
 built by concatenating the value of P and the digit `1'.  (You cannot achieve
 this by writing just `\P1', since `P1' is itself a valid name for a
 preprocessor variable.)


ΓòÉΓòÉΓòÉ 5.8.2. String and numeric constants ΓòÉΓòÉΓòÉ

There are two ways of writing string constants in gasp: as literal text, and by
numeric byte value.  Specify a string literal between double quotes ("str").
Specify an individual numeric byte value as an absolute expression between
angle brackets (<expr>.  Directives that output strings allow you to specify
any number of either kind of value, in whatever order is convenient, and
concatenate the result.  (Alternate syntax mode introduces a number of
alternative string notations; see Alternate macro syntax.)

You can write numeric constants either in a specific base, or in whatever base
is currently selected (either 10, or selected by the most recent .RADIX).

To write a number in a specific base, use the pattern s'ddd: a base specifier
character s, followed by a single quote followed by digits ddd.  The base
specifier character matches those you can specify with .RADIX: `B' for base 2,
`Q' for base 8, `D' for base 10, and `H' for base 16.  (You can write this
character in lower case if you prefer.)


ΓòÉΓòÉΓòÉ 5.8.3. Symbols ΓòÉΓòÉΓòÉ

gasp recognizes symbol names that start with any alphabetic character, `_', or
`$', and continue with any of the same characters or with digits.  Label names
follow the same rules.


ΓòÉΓòÉΓòÉ 5.8.4. Arithmetic expressions in GASP ΓòÉΓòÉΓòÉ

There are two kinds of expressions, depending on their result: absolute
expressions, which resolve to a constant (that is, they do not involve any
values unknown to gasp), and relocatable expressions, which must reduce to the
form

addsym+const-subsym

where addsym and subsym are assembly symbols of unknown value, and const is a
constant.

Arithmetic for gasp expressions follows very similar rules to C. You can use
parentheses to change precedence; otherwise, arithmetic primitives have
decreasing precedence in the order of the following list.

   1. Single-argument + (identity), - (arithmetic opposite), or ~ (bitwise
      negation).  The argument must be an absolute expression.

   2. * (multiplication) and / (division).  Both arguments must be absolute
      expressions.

   3. + (addition) and - (subtraction).  At least one argument must be
      absolute.

   4. & (bitwise and).  Both arguments must be absolute.

   5. | (bitwise or) and ~ (bitwise exclusive or; ^ in C).  Both arguments must
      be absolute.


ΓòÉΓòÉΓòÉ 5.8.5. String primitives ΓòÉΓòÉΓòÉ

You can use these primitives to manipulate strings (in the argument field of
gasp statements): .LEN("str") Calculate the length of string "str", as an
absolute expression.  For example, `.RES.B .LEN("sample")' reserves six bytes
of memory. .INSTR("string", "seg", ix) Search for the first occurrence of seg
after position ix of string.  For example, `.INSTR("ABCDEFG", "CDE", 0)'
evaluates to the absolute result 2.

The result is -1 if seg does not occur in string after position ix.
.SUBSTR("string",start,len) The substring of string beginning at byte number
start and extending for len bytes.


ΓòÉΓòÉΓòÉ 5.9. Alternate macro syntax ΓòÉΓòÉΓòÉ

If you specify `-a' or `--alternate' on the gasp command line, the preprocessor
uses somewhat different syntax.  This syntax is reminiscent of the syntax of
Phar Lap macro assembler, but it is not meant to be a full emulation of Phar
Lap or similar assemblers.  In particular, gasp does not support directives
such as DB and IRP, even in alternate syntax mode.

In particular, `-a' (or `--alternate') elicits these differences:

 Preprocessor directives
           You can use gasp preprocessor directives without a leading `.' dot.
           For example, you can write `SDATA' with the same effect as `.SDATA'.

 LOCAL
           One additional directive, LOCAL, is available. See Defining your own
           directives, for an explanation of how to use LOCAL.

 String delimiters
           You can write strings delimited in these other ways besides
           "string":

           'string'
                          You can delimit strings with single-quote charaters.

           <string>
                          You can delimit strings with matching angle brackets.

 single-character string escape
           To include any single character literally in a string (even if the
           character would otherwise have some special meaning), you can prefix
           the character with `!' (an exclamation mark).  For example, you can
           write `<4.3 !> 5.4!!>' to get the literal text `4.3 > 5.4!'.

 Expression results as strings
           You can write `%expr' to evaluate the expression expr and use the
           result as a string.


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