ack.7

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.TH ACK 7
.SH NAME
ACK \- Additional information on the Amsterdam Compiler Kit compilers
.SH DESCRIPTION
.de SP
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.\"
These are the details on the Amsterdam Compiler Kit compilers for the
languages C, Modula-2, and Pascal.  The design decisions that were made
where the respective standards allowed or mandated this, and the extensions
that were implemented.
.SH "ANSI C REPORT"
This section specifies the implementation-defined behavior of the ANSI-C
compiler as required by ANS X3.159-1989.
.NS A.6.3.1
.IP \(bu
Diagnostics are placed on the standard error output.  They have the
following specification:
.XS
"<file>", line <nr>: [(<class>)] <diagnostic>
.XE
There are three classes of diagnostics: 'error', 'strict' and 'warning'.
When the class is 'error', the class specification is absent.
The class 'strict' is used for violations of the standard which are
not severe enough to stop compilation, for example the occurrence
of non white-space after an '#endif' preprocessing
directive.  The class 'warning' is used for legal but dubious
constructions, for example the declaration of a structure-tag in a
parameter type list.
.NS A.6.3.2
.IP \(bu
The function 'main' can have zero or two parameters.  When it has two
parameters, the first parameter is an integer specifying the number of
arguments on the command line (including the command).  The second
parameter is a pointer to an array of pointers to the arguments
(as strings).
.IP \(bu
Interactive devices are terminals.
.NS A.6.3.3
.IP \(bu
The number of significant characters is 64.
Corresponding upper-case and lower-case letters are different.
.NS A.6.3.4
.IP \(bu
The compiler assumes ASCII-characters in both the source and execution
character set.
.IP \(bu
There are no multibyte characters.
.IP \(bu
There are 8 bits in a character.
.IP \(bu
Character constants that cannot be represented in 8 bits
are truncated.
.IP \(bu
Character constants that are more than 1 character wide will have the
first character specified in the least significant byte.
.IP \(bu
The only supported locale is 'C'.
.IP \(bu
A plain 'char' has the same range of values as 'signed char'.
.NS A.6.3.5
.IP \(bu
The i80x86 and 68000 both have a two's complement binary-number system.
Shorts are 2 bytes; ints are 2 bytes under 16-bits \*(Mp and 68000 \*(Mx, 4
bytes under 32-bits \*(Mp; longs occupy 4 bytes.
.IP \(bu
Converting an integer to a shorter signed integer is implemented by
ignoring the high-order byte(s) of the former.
Converting a unsigned integer to a signed integer of the same type is
only done in administration.  This means that the bit-pattern remains
unchanged.
.IP \(bu
The result of bitwise operations on signed integers are what can be
expected on a two's complement machine.
.IP \(bu
When either operand is negative, the result of the / operator is the
largest integer less than or equal to the algebraic quotient.
The sign of the remainder on integer division is the sign of the
enumerator.
.IP \(bu
The right-shift of a negative value is negative.
.NS A.6.3.6
.IP \(bu
The compiler uses IEEE format for floating-point numbers.
High-precision floating-point is used for constant folding.
.IP \(bu
Truncation is done to the nearest floating-point number that can
be represented.
.NS A.6.3.7
.IP \(bu
The type of the sizeof-operator (also known as size_t) is 'unsigned int'.
.IP \(bu
Casting an integer to a pointer or vice versa has no effect in
bit-pattern when the sizes are equal.  Otherwise the value will be
truncated or zero-extended (depending on the direction of the
conversion and the relative sizes).
.IP \(bu
The type of a 'ptrdiff_t' is 'int' on \*(Mp, and 'long' on the 68000
\*(Mx versions.
.NS A.6.3.8
.IP \(bu
Since the front end has only limited control over the registers, it can
only make it more likely that variables that are declared as
registers also end up in registers.  The only things that can possibly be
put into registers are plain ints and pointers.
.NS A.6.3.9
.IP \(bu
When a member of a union object is accessed using a member of a
different type, the resulting value will usually be garbage.  The
compiler makes no effort to catch these errors.
.IP \(bu
The alignment of types under 16-bit \*(Mp is 1 byte for characters and 2
bytes for all other types.  Under other MINIX 3 versions 'int' and smaller
types are aligned to a multiple of their size, bigger scalar types are
aligned like 'int'.  Arrays have the same alignment as their elements;
structs and unions are aligned like their field with the worst alignment.
.IP \(bu
A plain 'int' bit-field is taken as a 'signed int'.  This means that
a field with a size 1 bit-field can only store the values 0 and \(mi1.
.IP \(bu
In bit-fields, high-order bits are allocated first.
.IP \(bu
An enum has the same size as a plain 'int'.
.NS A.6.3.10
.IP \(bu
An access to a volatile object is either a load or a store.  Just
mentioning a volatile variable is not enough.
E.g. the statement 'x;' where x is declared volatile, does not
constitute an access.  When a volatile object should be read, but its
value ignored, 'if (x);' should do the trick.
.NS A.6.3.11
.IP \(bu
There is no fixed limit on the number of declarators that may modify an
arithmetic, structure or union type, although specifying too many may
cause the compiler to run out of memory.
.NS A.6.3.12
.IP \(bu
The maximum number of cases in a switch-statement is in the order of
1e9, although the compiler may run out of memory somewhat earlier.
.NS A.6.3.13
.IP \(bu
Since both the preprocessor and the compiler assume ASCII-characters, 
a single character constant in a conditional-inclusion directive
matches the same value in the execution character set.
.IP \(bu
The preprocessor recognizes \fI\(enI...\fR command-line options.  The
directories thus specified are searched first.  After that, /usr/include is
visited.
.IP \(bu
Quoted names are first looked for in the directory in which the file
which does the include resides.
.IP \(bu
The characters in a h- or q- char-sequence are taken to be
.UX
paths.
.IP \(bu
Neither the front-end nor the preprocessor know any pragmas.
.IP \(bu
Since the compiler runs on 
.MX ,
_\^_DATE_\^_ and _\^_TIME_\^_ will always be
defined.
.NS A.6.3.14
.IP \(bu
NULL is defined as ((void *)0).  This in order to detect dubious
constructions like 'int x = NULL;'.
.IP \(bu
The diagnostic printed by 'assert' is as follows:
.XS
Assertion "<expr>" failed, file "<file>", line <line>
.XE
where <expr> is the argument to the assert macro, printed as string.
(the <file> and <line> should be clear)
.IP \(bu
The sets for character test macros for the C locale are as follows:
.XS
.ta +\w'isalnum    'u
\fBName	Set\fR
\fIisalnum\fR	0-9A-Za-z
\fIisalpha\fR	A-Za-z
\fIiscntrl\fR	\e000-\e037\e177
\fIislower\fR	a-z
\fIisupper\fR	A-Z
\fIisprint\fR	\e040-\e176
.DT
.XE
As an addition, there is an \fIisascii\fR macro, which tests whether a character
is an ASCII character.  Characters in the range from \e000 to \e177 are ASCII
characters.
.IP \(bu
The behavior of ACK mathematical functions on domain error is as follows:
.XS
.ta +\w'log10   'u
\fBName	Returns\fR
\fIasin\fR	0.0
\fIacos\fR	0.0
\fIatan2\fR	0.0
\fIfmod\fR	0.0
\fIlog\fR	\(miHUGE_VAL
\fIlog10\fR	\(miHUGE_VAL
\fIpow\fR	0.0
\fIsqrt\fR	0.0
.DT
.XE
\*(Mv uses the BSD4.4 C library and the Sun FDLIBM C math library instead
of the ACK library.  See
.BR math (3)
for details about the math functions.  The \*(Mv libraries offer at
least the same functionality as the ACK library.
.IP \(bu
Underflow range errors do not cause \fIerrno\fR to be set.
.IP \(bu
The function \fIfmod\fR returns 0.0 and sets \fIerrno\fR to EDOM when the second
argument is 0.0.
.IP \(bu
The set of signals for the \fIsignal\fR function is as described by
.BR sigaction (2).
.IP \(bu
A text-stream need not end in a new-line character.
.IP \(bu
White space characters before a new-line appear when read in.
.IP \(bu
There may be any number of null characters appended to a binary
stream.
.IP \(bu
The file position indicator of an append mode stream is initially
positioned at the beginning of the file.
.IP \(bu
A write on a text stream does not cause the associated file to be
truncated beyond that point.
.IP \(bu
The buffering intended by the standard is fully supported.
.IP \(bu
A zero-length file actually exists.
.IP \(bu
A file name can consist of any character, except for the '\e0' and
the '/'.
.IP \(bu
A file can be open multiple times.
.IP \(bu
When a \fIremove\fR is done on an open file, reading and writing behave
just as can be expected from a non-removed file.  When the associated
stream is closed, however, all written data will be lost.
.IP \(bu
When a file exists prior to a call to \fIrename\fR, it is removed.
.IP \(bu
The %p conversion in \fIfprintf\fR has the same effect as %#x on \*(Mp and
%#lx on the 68000 versions of \*(Mx.
.IP \(bu
The %p conversion in \fIfscanf\fR has the same effect as %x on \*(Mp and
%lx on the 68000 versions of \*(Mx.
.IP \(bu
A \(mi character that is neither the first nor the last character in the
scanlist for %[ conversion is taken to be a range indicator.  When the
first character has a higher ASCII-value than the second, the \(mi will
just be put into the scanlist.
.IP \(bu
The value of \fIerrno\fR when \fIfgetpos\fR or \fIftell\fR failed is that of \fIlseek\fR.
This means:
.XS
.ta +\w'ESPIPE   'u +\w'\- 'u
EBADF	\-	when the stream is not valid
ESPIPE	\-	when fildes is associated with a pipe
EINVAL	\-	the resulting file pointer would be negative
.XE
.IP \(bu
The messages generated by \fIperror\fR depend on the value of \fIerrno\fR.
The mapping of errors to strings is done by \fIstrerror\fR.
.IP \(bu
When the requested size is zero, \fImalloc\fR, \fIcalloc\fR and \fIrealloc\fR
return a null-pointer under \*(Mx.  Under \*(Mv a unique non-null pointer is
returned.
.IP \(bu
When \fIabort\fR is called, output buffers will be flushed.  Temporary files
(made with the \fItmpfile\fR function) will have disappeared when SIGABRT
is not caught or ignored.
.IP \(bu
The \fIexit\fR function returns the low-order eight bits of its argument
to the environment.
.IP \(bu
The predefined environment names are controlled by the user.
Setting environment variables is done through the \fIputenv\fR function.
This function accepts a pointer to char as its argument.
To set, for example, the environment variable TERM to a230 one writes
.XS
static char terminal[] = "TERM=a230";
putenv(terminal);
.XE
The argument to \fIputenv\fR is stored in an internal table, so malloc'ed
strings cannot be freed until another call to \fIputenv\fR (which sets the
same environment variable) is made.  The argument to \fIputenv\fR must be
writable, which means that officially, the argument cannot be a string
constant.
The function returns 1 if it fails, 0 otherwise.
.LP
.IP \(bu
The argument to \fIsystem\fR is passed as argument to \fI/bin/sh \(enc\fR.
.IP \(bu
The strings returned by \fIstrerror\fR depend on \fIerrno\fR.  They are
listed in
.BR intro (2).
Everything else causes \fIstrerror\fR to return "unknown error" under \*(Mx,
or the result of sprintf("Error %d", errno) under \*(Mv.
.IP \(bu
The local time zone is per default GMT.  This can be
changed through the TZ environment variable, e.g. TZ=EST6.
See
.BR TZ (5).
.IP \(bu
The \fIclock\fR function returns the number of ticks since process
startup.
.SS References
.IP [1]
ANS X3.159-1989
.ft I
American National Standard for Information Systems -
Programming Language C
.ft R
.SH "THE MINIX MODULA-2 COMPILER"
This section describes the implementation-specific features of the
.MX
Modula-2 compiler.
It is not intended to teach Modula-2 programming.
For a description of the Modula-2 language,
the reader is referred to [1].
.SS "The language implemented"
.PP
This paragraph discusses the deviations from the Modula-2 language as described
in the 'Report on The Programming Language Modula-2',
as it appeared in [1],
from now on referred to as 'the Report'.
Also,
the Report sometimes leaves room for interpretation.
The section numbers
mentioned are the section numbers of the Report.
.SS "Syntax (section 2)"
.PP
The syntax recognized is that of the Report,
with some extensions to
also recognize the syntax of an earlier definition,
given in [2].
Only one compilation unit per file is accepted.
.SS "Vocabulary and Representation (section 3)"
.PP
The input '\*(Cw10..\fR' is parsed as two tokens: '\*(Cw10\fR' and '\*(Cw..\fR'.
.PP
The empty string \*(Cw""\fR has type
.XS
.CW
ARRAY [0 .. 0] OF CHAR
.ft P
.XE
and contains one character: \*(Cw0C\fR.
.PP
When the text of a comment starts with a '\*(Cw$\fR',
it may be a pragma.
Currently,
the following pragmas exist:
.nf
.SP
.CW
(*$F      (F stands for Foreign) *)
(*$R[+|-] (Runtime checks, on or off, default on) *)
(*$A[+|-] (Array bound checks, on or off, default off) *)
(*$U      (Allow for underscores within identifiers) *)
.ft P
.SP
.fi
The Foreign pragma is only meaningful in a \*(CwDEFINITION MODULE\fR,
and indicates that this
\*(CwDEFINITION MODULE\fR describes an interface to a module written in another
language (for instance C or Pascal).
Runtime checks that can be disabled are:
range checks,
\*(CwCARDINAL\fR overflow checks,
checks when assigning a \*(CwCARDINAL\fR to an \*(CwINTEGER\fR and vice versa,
and checks that \*(CwFOR\fR-loop control-variables are not changed
in the body of the loop.
Array bound checks can be enabled,
because many EM implementations do not
implement the array bound checking of the EM array instructions.
When enabled,
the compiler generates a check before generating an
EM array instruction.