The Vax version of as
accepts any of the following options,
gives a warning message that the option was ignored and proceeds.
These options are for compatibility with scripts designed for other
people's assemblers.
-D
(Debug)
-S
(Symbol Table)
-T
(Token Trace)
-d
(Displacement size for JUMPs)
-V
(Virtualize Interpass Temporary File)
as
always does this, so this
option is redundant.
-J
(JUMPify Longer Branches)
-t
(Temporary File Directory)
as
does not use a temporary disk file, this
option makes no difference. `-t' needs exactly one
filename.
The Vax version of the assembler accepts two options when
compiled for VMS. They are `-h', and `-+'. The
`-h' option prevents as
from modifying the
symbol-table entries for symbols that contain lowercase
characters (I think). The `-+' option causes as
to
print warning messages if the FILENAME part of the object file,
or any symbol name is larger than 31 characters. The `-+'
option also inserts some code following the `_main'
symbol so that the object file is compatible with Vax-11
"C".
Conversion of flonums to floating point is correct, and compatible with previous assemblers. Rounding is towards zero if the remainder is exactly half the least significant bit.
D
, F
, G
and H
floating point formats
are understood.
Immediate floating literals (e.g. `S`$6.9') are rendered correctly. Again, rounding is towards zero in the boundary case.
The .float
directive produces f
format numbers.
The .double
directive produces d
format numbers.
The Vax version of the assembler supports four directives for generating Vax floating point constants. They are described in the table below.
.dfloat
d
format 64-bit floating point constants.
.ffloat
f
format 32-bit floating point constants.
.gfloat
g
format 64-bit floating point constants.
.hfloat
h
format 128-bit floating point constants.
All DEC mnemonics are supported. Beware that case...
instructions have exactly 3 operands. The dispatch table that
follows the case...
instruction should be made with
.word
statements. This is compatible with all unix
assemblers we know of.
Certain pseudo opcodes are permitted. They are for branch instructions. They expand to the shortest branch instruction that reaches the target. Generally these mnemonics are made by substituting `j' for `b' at the start of a DEC mnemonic. This feature is included both for compatibility and to help compilers. If you do not need this feature, avoid these opcodes. Here are the mnemonics, and the code they can expand into.
jbsb
jbr
jr
jCOND
neq
, nequ
, eql
, eqlu
, gtr
,
geq
, lss
, gtru
, lequ
, vc
, vs
,
gequ
, cc
, lssu
, cs
.
COND may also be one of the bit tests
bs
, bc
, bss
, bcs
, bsc
, bcc
,
bssi
, bcci
, lbs
, lbc
.
NOTCOND is the opposite condition to COND.
jacbX
b d f g h l w
.
OPCODE ..., foo ; brb bar ; foo: jmp ... ; bar:
jaobYYY
lss leq
.
jsobZZZ
geq gtr
.
OPCODE ..., foo ; brb bar ; foo: brw destination ; bar:
OPCODE ..., foo ; brb bar ; foo: jmp destination ; bar:
aobleq
aoblss
sobgeq
sobgtr
OPCODE ..., foo ; brb bar ; foo: brw destination ; bar:
OPCODE ..., foo ; brb bar ; foo: jmp destination ; bar:
The immediate character is `$' for Unix compatibility, not `#' as DEC writes it.
The indirect character is `*' for Unix compatibility, not `@' as DEC writes it.
The displacement sizing character is ``' (an accent grave) for
Unix compatibility, not `^' as DEC writes it. The letter
preceding ``' may have either case. `G' is not
understood, but all other letters (b i l s w
) are understood.
Register names understood are r0 r1 r2 ... r15 ap fp sp
pc
. Upper and lower case letters are equivalent.
For instance
tstb *w`$4(r5)
Any expression is permitted in an operand. Operands are comma separated.
Vax bit fields can not be assembled with as
. Someone
can add the required code if they really need it.
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