Document revision date: 30 March 2001

This chapter describes the following components of VAX MACRO source statements:

• Character set
• Numbers
• Symbols
• Local labels
• Terms and expressions
• Unary and binary operators
• Direct assignment statements
• Current location counter

The following characters can be used in VAX MACRO source statements:

• The letters of the alphabet, A to Z, uppercase and lowercase. Note that the assembler considers lowercase letters equivalent to uppercase letters except when they appear in ASCII strings.
• The digits 0 to 9.
• The special characters listed in Table 3-1.

Table 3-1 Special Characters Used in VAX MACRO Statements

Character	Character Name	Function
_	Underscore	Character in symbol names
$	Dollar sign	Character in symbol names
.	Period	Character in symbol names, current location counter, and decimal point
:	Colon	Label terminator
=	Equal sign	Direct assignment operator and macro keyword argument terminator
	Tab	Field terminator
	Space	Field terminator
#	Number sign	Immediate addressing mode indicator
@	At sign	Deferred addressing mode indicator and arithmetic shift operator
,	Comma	Field, operand, and item separator
;	Semicolon	Comment field indicator
+	Plus sign	Autoincrement addressing mode indicator, unary plus operator, and arithmetic addition operator
-	Minus sign or hyphen	Autodecrement addressing mode indicator, unary minus operator, arithmetic subtraction operator, and line continuation indicator
*	Asterisk	Arithmetic multiplication operator
/	Slash	Arithmetic division operator
&	Ampersand	Logical AND operator
!	Exclamation point	Logical inclusive OR operator point
\	Backslash	Logical exclusive OR and numeric conversion indicator in macro arguments
^	Circumflex	Unary operators and macro argument delimiter
[ ]	Square brackets	Index addressing mode and repeat count indicators
( )	Parentheses	Register deferred addressing mode indicators
<>	Angle brackets	Argument or expression grouping delimiters
?	Question mark	Created local label indicator in macro arguments
'	Apostrophe	Macro argument concatenation indicator
%	Percent sign	Macro string operators

Table 3-2 defines the separating characters used in VAX MACRO.

Table 3-2 Separating Characters in VAX MACRO Statements

Character	Character Name	Usage
(space) (tab)	Space or tab	Separator between statement fields. Spaces within expressions are ignored.
,	Comma	Separator between symbolic arguments within the operand field. Multiple expressions in the operand field must be separated by commas.

3.2 Numbers

Numbers can be integers, floating-point numbers, or packed decimal strings.

3.2.1 Integers

Format

snn

s

An optional sign: plus sign (+) for positive numbers (the default) or minus sign (-) for negative numbers.

nn

A string of numeric characters that is legal for the current radix.

VAX MACRO interprets all integers in the source program as decimal unless the number is preceded by a radix control operator (see Section 3.6.1).

Integers must be in the range of -2,147,483,648 to +2,147,483,647 for signed data or in the range of 0 to 4,294,967,295 for unsigned data.

Negative numbers must be preceded by a minus sign; VAX MACRO translates such numbers into two's complement form. In positive numbers, the plus sign is optional.

3.2.2 Floating-Point Numbers

A floating-point number can be used in the .F_FLOATING (.FLOAT),.D_FLOATING (.DOUBLE), .G_FLOATING, and .H_FLOATING directives (described in Chapter 6) or as an operand in a floating-point instruction. A floating-point number cannot be used in an expression or with a unary or binary operator except the unary plus, unary minus, and unary floating-point operator, ^F (F_FLOATING). Section 3.6 and Section 3.7 describe unary and binary operators.

A floating-point number can be specified with or without an exponent.

Formats

Floating-point number without exponent:

snn
snn.nn
snn.

Floating-point number with exponent:

snnEsnn
snn.nnEsnn
snn.Esnn

s

An optional sign.

nn

A string of decimal digits in the range of 0 to 9.

The decimal point can appear anywhere to the right of the first digit. Note that a floating-point number cannot start with a decimal point because VAX MACRO will treat the number as a user-defined symbol (see Section 3.3.2).

Floating-point numbers can be single-precision (32-bit), double-precision (64-bit), or extended-precision (128-bit) quantities. The degree of precision is 7 digits for single-precision numbers, 16 digits for double-precision numbers, and 33 digits for extended-precision numbers.

The magnitude of a nonzero floating-point number cannot be smaller than approximately 0.29E-38 or greater than approximately 1.7E38.

Single-precision floating-point numbers can be rounded (by default) or truncated. The .ENABLE and .DISABLE directives (described in Chapter 6) control whether single-precision floating-point numbers are rounded or truncated. Double-precision and extended-precision floating-point numbers are always rounded.

Section 8.3.6, Section 8.3.7, Section 8.3.8, and Section 8.3.9 describe the internal format of floating-point numbers.

3.2.3 Packed Decimal Strings

A packed decimal string can be used only in the .PACKED directive (described in Chapter 6).

Format

snn

s

An optional sign.

nn

A string containing up to 31 decimal digits in the range of 0 to 9.

A packed decimal string cannot have a decimal point or an exponent.

Section 8.3.14 describes the internal format of packed decimal strings.

3.3 Symbols

Three types of symbols can be used in VAX MACRO source programs: permanent symbols, user-defined symbols, and macro names.

3.3.1 Permanent Symbols

Permanent symbols consist of instruction mnemonics (see Appendix D), VAX MACRO directives (see Chapter 6), and register names. You need not define instruction mnemonics and directives before you use them in the operator field of a VAX MACRO source statement. Also, you need not define register names before using them in the addressing modes (see Chapter 5).

Register names cannot be redefined; that is, a symbol that you define cannot be one of the register names contained in the following list. You can express the 16 general registers of the VAX processor in a source program only as follows:

Register Name	Processor Register
R0	General register 0
R1	General register 1
R2	General register 2
.	.
.	.
.	.
R11	General register 11
R12 or AP	General register 12 or argument pointer. If you use R12 as an argument pointer, the name AP is recommended; if you use R12 as a general register, the name R12 is recommended.
FP	Frame pointer
SP	Stack pointer
PC	Program counter

Note that the symbols IV and DV are also permanent symbols and cannot be redefined. These symbols are used in the register mask to set the integer overflow trap (IV) and the decimal string overflow trap (DV). See Section 3.6.2.2 for an explanation of their uses.

3.3.2 User-Defined Symbols and Macro Names

You can use symbols that you define as labels or you can equate them to a specific value by a direct assignment statement (see Section 3.8). These symbols can also be used in any expression (see Section 3.5).

The following rules govern the creation of user-defined symbols:

• User-defined symbols can be composed of alphanumeric characters, underscores (_), dollar signs ($), and periods (.). Any other character terminates the symbol.
• The first character of a symbol must not be a number.
• The symbol must be no more than 31 characters long and must be unique.

In addition, by Compaq convention:

• The dollar sign ($) is reserved for names defined by Compaq. This convention ensures that a user-defined name (which does not have a dollar sign) will not conflict with a Compaq-defined name (which does have a dollar sign).
• Do not use the period (.) in any global symbol name (see Section 3.3.3) because languages, such as FORTRAN, do not allow periods in symbol names.

Macro names follow the same rules and conventions as user-defined symbols. (See the description of the .MACRO directive in Chapter 6 for more information on macro names.) User-defined symbols and macro names do not conflict; that is, the same name can be used for a user-defined symbol and a macro. To avoid confusion, give the symbols and macros that you define different names.

3.3.3 Determining Symbol Values

The value of a symbol depends on its use in the program. VAX MACRO uses a different method to determine the values of symbols in the operator field than it uses to determine the values of symbols in the operand field.

A symbol in the operator field can be either a permanent symbol or a macro name. VAX MACRO searches for a symbol definition in the following order:

1. Previously defined macro names
2. User-defined opcode (see the .OPDEF description in Chapter 6)
3. Permanent symbols (instructions and directives)
4. Macro libraries

This search order allows permanent symbols to be redefined as macro names. If a symbol in the operator field is not defined as a macro or a permanent symbol, the assembler displays an error message.

A symbol in the operand field must be either a user-defined symbol or a register name.

User-defined symbols can be either local (internal) symbols or global (external) symbols. Whether symbols are local or global depends on their use in the source program.

A local symbol can be referenced only in the module in which it is defined. If local symbols with the same names are defined in different modules, the symbols are completely independent. The definition of a global symbol, however, can be referenced from any module in the program.

VAX MACRO treats all symbols that you define as local unless you explicitly declared them to be global by doing any one of the following:

• Use the double colon (::) in defining a label (see Section 2.1).
• Use the double equal sign (==) in a direct assignment statement (see Section 3.8).
• Use the .GLOBAL, .ENTRY, or .WEAK directive (see Chapter 6).

When your code references a symbol within the module in which it is defined, VAX MACRO considers the reference internal. When your code references a symbol within a module in which it is not defined, VAX MACRO considers the reference external (that is, the symbol is defined externally in another module). You can use the .DISABLE directive to make references to symbols not defined in the current module illegal. In this case, you must use the .EXTERNAL directive to specify that the reference is an external reference. See Chapter 6 for descriptions of the .DISABLE and .EXTERNAL directives.

3.4 Local Labels

Use local labels to identify addresses within a block of source code.

Format

nn$

nn

A decimal integer in the range of 1 to 65535.

Use local labels in the same way as you use the symbol labels that you define, with the following differences:

• Local labels cannot be referenced outside the block of source code in which they appear.
• Local labels can be reused in another block of source code.
• Local labels do not appear in the symbol tables and thus cannot be accessed by the VAX Symbolic Debugger.
• Local labels cannot be used in the .END directive (see Chapter 6).

By convention, local labels are positioned like statement labels: left-justified in the source text. Although local labels can appear in the program in any order, by convention, the local labels in any block of source code should be in numeric order.

Local labels are useful as branch addresses when you use the address only within the block. You can use local labels to distinguish between addresses that are referenced only in a small block of code and addresses that are referenced elsewhere in the module. A disadvantage of local labels is that their numeric names cannot provide any indication of their purpose. Consequently, you should not use local labels to label sequences of statements that are logically unrelated; user-defined symbols should be used instead.

Compaq recommends that users create local labels only in the range of 1$ to 29999$ because the assembler automatically creates local labels in the range of 30000$ to 65535$ for use in macros (see Section 4.7).

The local label block in which a local label is valid is delimited by the following statements:

• A user-defined label
• A .PSECT directive (see Chapter 6)
• The .ENABLE and .DISABLE directives (see Chapter 6), which can extend a local label block beyond user-defined labels and .PSECT directives

A local label block is usually delimited by two user-defined labels. However, the .ENABLE LOCAL_BLOCK directive starts a local block that is terminated only by one of the following:

• A second .ENABLE LOCAL_BLOCK directive
• A .DISABLE LOCAL_BLOCK directive followed by a user-defined label or a .PSECT directive

Although local label blocks can extend from one program section to another, Compaq recommends that local labels in one program section not be referenced from another program section. User-defined symbols should be used instead.

Local labels can be preserved for future reference with the context of the program section in which they are defined; see the descriptions of the .SAVE_PSECT [LOCAL_BLOCK] directive and the .RESTORE_PSECT directive in Chapter 6.

An example showing the use of local labels follows:

RPSUB: MOVL AMOUNT,R0 ; Start local label block 10$: SUBL2 DELTA,R0 ; Define local label 10$ BGTR 10$ ; Conditional branch to local label ADDL2 DELTA,R0 ; Executed when R0 not > 0 COMP: MOVL MAX,R1 ; End previous local label CLRL R2 ; block and start new one 10$: CMPL R0,R1 ; Define new local label 10$ BGTR 20$ ; Conditional branch to local label SUBL INCR,R0 ; Executed when R0 not > R1 INCL R2 ; . . . BRB 10$ ; Unconditional branch to local label 20$: MOVL R2,COUNT ; Define local label BRW TEST ; Unconditional branch to user-defined label .ENABLE LOCAL_BLOCK ; Start local label block that ENTR1: POPR #^M<R0,R1,R2> ; will not be terminated ADDL3 R0,R1,R3 ; by a user-defined label BRB 10$ ; Branch to local label that appears ; after a user-defined label ENTR2: SUBL2 R2,R3 ; Does not start a new local label block 10$: SUBL2 R2,R3 ; Define local label BGTR 20$ ; Conditional branch to local label INCL R0 ; Executed when R2 not > R3 BRB NEXT ; Unconditional branch to user-defined label 20$: DECL R0 ; Define local label .DISABLE LOCAL_BLOCK ; Directive followed by user-defined NEXT: CLRL R4 ; label terminates local label block

3.5 Terms and Expressions

A term can be any of the following:

• A number
• A symbol
• The current location counter (see Section 3.9)
• A textual operator followed by text (see Section 3.6.2)
• Any of the previously noted items preceded by a unary operator (see Section 3.6)

VAX MACRO evaluates terms as longword (4-byte) values. If you use an undefined symbol as a term, the linker determines the value of the term. The current location counter (.) has the value of the location counter at the start of the current operand.

Expressions are combinations of terms joined by binary operators (see Section 3.7) and evaluated as longword (4-byte) values. VAX MACRO evaluates expressions from left to right with no operator precedence rules. However, angle brackets (<>) can be used to change the order of evaluation. Any part of an expression that is enclosed in angle brackets is first evaluated to a single value, which is then used in evaluating the complete expression. For example, the expressions A*B+C and A*<B+C> are different. In the first case, A and B are multiplied and then C added to the product. In the second case, B and C are added and the sum is multiplied by A. Angle brackets can also be used to apply a unary operator to an entire expression, such as -<A+B>.

If an arithmetic expression is continued on another line, the listing file will not show the continued line. For example:

.WORD <DATA1'$^XFF@8+- 89>

You must use /LIST/SHOW=EXPANSION to show the continuation line.

VAX MACRO considers unary operators part of a term and thus, performs the action indicated by a unary operator before it performs the action indicated by any binary operator.

Expressions fall into three categories: relocatable, absolute, and external (global), as follows:

• An expression is relocatable if its value is fixed relative to the start of the program section in which it appears. The current location counter is relocatable in a relocatable program section.
• An expression is absolute if its value is an assembly-time constant. An expression whose terms are all numbers is absolute. An expression that consists of a relocatable term minus another relocatable term from the same program section is absolute, since such an expression reduces to an assembly-time constant.
• An expression is external if it contains one or more symbols that are not defined in the current module.

Any type of expression can be used in most MACRO statements, but restrictions are placed on expressions used in the following:

• .ALIGN alignment directives
• .BLKx storage allocation directives
• .IF and .IIF conditional assembly block directives
• .REPEAT repeat block directives
• .OPDEF opcode definition directives
• .ENTRY entry point directives
• .BYTE, .LONG, .WORD, .SIGNED_BYTE, and .SIGNED_WORD directive repetition factors
• Direct assignment statements (see Section 3.8)

See Chapter 6 for descriptions of the directives listed in the preceding list.

Expressions used in these directives and in direct assignment statements can contain only symbols that have been previously defined in the current module. They cannot contain either external symbols or symbols defined later in the current module. In addition, the expressions in these directives must be absolute. Expressions in direct assignment statements can be relocatable.

An example showing the use of expressions follows.

A = 2*100 ; 2*100 is an absolute expression .BLKB A+50 ; A+50 is an absolute expression and ; contains no undefined symbols LAB: .BLKW A ; LAB is relocatable HALF = LAB+<A/2> ; LAB+<A/2> is a relocatable ; expression and contains no ; undefined symbols LAB2: .BLKB LAB2-LAB ; LAB2-LAB is an absolute expression ; and contains no undefined symbols ; but contains the symbol LAB3 ; that is defined later in this module LAB3: .WORD TST+LAB+2 ; TST+LAB+2 is an external expression ; because TST is an external symbol

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