LOCATION COUNTER DEFINITION

A procedure may be made to generate code under one or more location counters by defining the location counter in the label field of a line item within the procedure sample. When the procedure is completed, the location counter active at the time that the procedure was called is reactivated.

Example:

000001 ^{/ .}

000002 ^A· PROC

00U003 SLJI ^{S (1)}

00000'1 ^{S(l) +A (} 1 ,11

0000 aS END

000U06

00U007

.

000008

000C.l09 00 oOoouo 30 0000 A SUBI

+ 6.12 Cd U 01 0 0 0000 000000

+ Ie 00 SUal

000010 00 000001 30 000 1 SUBZ

+ 6. 12 a ^I

U 01 000001 000000

+ 18 00 SUe2

000011 END

••• ^SUMMARY •••

PROGRAM 5IZE: 00 00002 01 00002

EXTERNAL OR UNDEfINED REFERENCES: suez SUSI

Explanation:

• Lines 2 and 5 define the proced ure A.

• Line 3 generates an S LJ I instruction to the next word under location counter 1.

• Line 4 defines the subroutine entry address under location counter 1.

• Lines 9 and 10 generate two calls on subroutines SUBI and SUB2 respectively.

The SLJI instructions are generated under location counter 0; the entry point addresses, SUB1 and SUB2, are generated under location counter 1.

NO T E: Unless a map is s ubm itted to force location counters 0 and 1 to be in the same bay, the foregoing example is not executable.

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3.11.1. Writing Labels

A label may be affixed to the line of reference to a procedure. Under normal conditions, this label is defined as equal to the value of the current location counter at the time of the procedure call. It is possible to associate this label with a line within the procedure. This is done by coding an asterisk (*) alone in the label field of that particular line in the procedure. The label of the calling line is processed exactly as though it has appeared in place of the asterisk except that it is defined at the level of the reference line on which it appeared.

Example:

000001 ^{/ .}

000002 A- PROC I. Z

OOOOOl ^TZ ACId'

00000'+

-

OOOOO~ END

0011006

00uQ07

. _---

000008

00v009 00 000000 51 000 3 JP A ONE,TWQ

00 OOOOul 3'1 000'+

OO[JU10 00 000002 ^S!) 0001 JI JP

00G011 00 OOOOu3 000001 ONE + I

000012 00 OUooo,+ 000002 TIIO +2

001.1013 END

Expla nation:

• Lines 2 and 5 define the proced ure A, which generates the instructions TZ and J.

• Line 4 generates the instruction J and has a single asterisk in the label field.

• Line 9 calls on procedure A. The label JP is defined as equal to the location counter value of the J instruction instead of the usual TZ instruction which is the first line generated.

3.12. Complex Procedures

The following paragraphs of this section contain a discussion of those assembler features which enable the construction and use of complex procedures. When the DO, NAME, and GO directives are used in conjunction with procedures, a powerful tool exis ts for the ge nera tion of code wh ich is cond itioned by the supplied parameters.

Procedures may be used to conditionally generate code. The PROC structure enables coding of generation alogrithms in the procedure sample, such that the code generated applies the alogrithms a nd rna y gene rate entire ly d ifferen t tables or instructions, depending on the supplied parameters.

3.12.1. NAME Directive

The NAME directive has three functions:

• It provides a local reference point within a given procedure sample.

• It provides alternate entry points to the procedure.

• It may supply a value to the procedure which is unique for the associated entry point.

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3.12.1.1. Local Reference Point

The NAME directive provides a local reference point within the procedure sample

3.12.1.2. Alternate Entry Point

The NAME directive may be used as an alternate entry point to the procedure.

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Example 1:

E.XTERNAL OR UNOEflNlO REfERENCES: MOVSU6

••••

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Expla nation:

• Lines 2 and 13 define the procedure X.

• Line 3 provides the entry point MOVE.

• Lines 4 and 5 generate LV and LL if the first two parameters are preceded by an asteris k.

• The GO directive on line 6 w ill be performed if the third parameter is preceded by an asterisk. If so, lines 7 and 8 are ignored and the procedure subassembly resumes at line 9.

• If no asterisk appears in the third parameter, line 7 generates a BT instruction.

• Line 8 terminates the subassembly of the procedure. Note that the DO statement is used to avoid the termination of the procedure sample which would result if just an END statement were coded.

II Lines 10 and 11 generate either LBK or LB, depending on the number of words to be transferred.

• Line 12 generates an SLJI call on the subroutine MOVSUB.

• Line 17 calls on the procedure X through the MOVE entry. Since no asterisk precedes the third parameter, a BT 12 instruction is generated in addition to

the LV and LL instructions.

• Line 18 calls on the sam e proced ure but because the third parameter is preceded by an asteris k, the code generated is:

LU (FROM) LL (TO) LBK 120 SLJI (MOVSVB)

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DO Xll,3)<01l0UO, loBI< Xll,3)

000018

tXT~~NAI. OR UNliEfIN£O REFERENCES:

Explanation: caused by using the GO directive inappropriately.

3.12.3. DO Directive

The DO directive, as previously explained, is used to conditionally generate one or more words of data. The DO directive in the assembler is a powerful tool which, when used within procedures, provides great flexibility and power. When combined with the GO directive, the DO directive can be used to generate series of instructions iterative ly as we 11 as c ond itionally. The follow ing paragraphs detail the rules which apply when these two directives are used together.

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• Line 4 cOHlbines a DO and GO directive. Since the paraform X may have a value between 0 and infinity (actually the maximum number of fields allowed is 1768), it may be either a conditional or generative DO. Assuming X>l, the DO is of the generative type. As a result the GO Xl is performed X times.

Each time, transfer is made to line 6, and the procedures LA and SA are performed. After the DO count is exhausted, line 5, which terminates the subassembly, is performed. If X=l, transfer to line 6 is made, and subassembly is terminated upon encountering the END directive in line 9.

• Line 7 calls the procedure LA, which generates the instructions LU and LL.

• Line 8 calls the procedure SA, which generates an SU and SL.

• Line 13 calls on the procedure X and generates the instructions:

LU

A

LL A+l SU

B

SL B+l LU C LL C+l SU D

and so on through F.

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ccc~=_~rc .-L.. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ... _ _ _ _ _ ... _ _ _ _ _ _ --'-_ _ _ _ m ___ c_

• Line 15 calls on the procedure through entry point CALLIO to generate the ins tructions:

SLJI (OPEN) LLK 1 SLJI (GET) LLK 3 SLJI (GET) LLK 5 SLJI (GET) SLJI (CLOSE)

• Line 16 calls on the procedure through entry point CALLIO to generate the instructions:

SLJI (OPEN) LLK 2 SLJI (GET) SLJI (CLOSE)

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