Program Logic Manual - All about the IBM 1130 Computing System

A DO Table entry is made for each DO statementwhen it is detected. As the statements followingthe DO statement are scanned, the statement numbersare compared with the contents of word 5, therange limit, of the DO Table entries. When therange limit is found the DO test coding is insertedinto the statement string.The DO Table is built from low-to-high-addressedstorage. It is scanned, however, from high-to-lowaddressedstorage. In this manner, nested DO loopsthat violate range limits are detected.Errors DetectedThe following errors are detected in phase 14: 51,52, 53, 54, 55, 56, 57, 58, 59, 60, 61, and 62.PHASE :L5• Scans READ, WRTEE, IF, CALL, and arithmeticstatements for subscript expressions.• Optimizes subscript calculation by means of theSubscript Expression Table.• Generates SGTs (Subscript-generated temporarystorage locations) as necessary.Each unique subscript expression is placed into atable called the Subscript Expression Table. Eachentry in this table appears as follows:Word Contents1 D 42 I, first dimension subscript index3 D 14 J, second dimension subscript index5 D 26 K, third dimension subscript index7 D 38 /8010, if entry is not used/0010, if entry is used on this statement/0000, if entry was used on a previousstatementAlso, each unique variable of a subscript expressionis placed into a table called the Bound VariableTable.As each subscript expression is entered into theSubscript Expression Table, it is removed from thestring. The subscripted variable is then tagged withSGT indicator bits pointing to the Subscript ExpressionTable entry.An SGT (Subscript-generated temporary storagelocation) is generated for each entry made to the SubscriptExpression Table. The SGT is placed into anSGT Table. The SGT is also placed into the SymbolTable and the address of the Symbol Table entry isinserted into the statement in the string.For each subscript expression encountered, ascan is made of the Bound Variable Table. If one ormore of the variables in the subscript expression arenot located in the Bound Variable Table, the subscriptmust be recalculated. Thus, a unique entry is madeto the Subscript Expression Table for the expressionand an associated SGT is generated.If, however, all the variables of the subscriptexpression are located in the Bound Variable Table,the Subscript Expression Table is then scanned todetermine if a duplicate subscript expression is alreadylocated in the table. If no equivalent is found,the subscript expression is added to the table as aunique entry and an associated SGT is generated.If a duplicate expression is found in the SubscriptExpression Table, the subscript expression is removedfrom the string and is replaced by a pointerto its duplicate in the Subscript Expression Table.Thus, identical subscript expressions share the sameindices of a common entry in the Subscript ExpressionTable and the same SGT.Whenever a variable is assigned a new value (i. e. ,appears to the left of the equal sign in an arithmeticexpression, in the argument list of a subprogram,etc.), that variable, if found in the Bound VariableTable, is removed from the table. This removalfrom the Bound Variable Table causes all entries inthe Subscript Expression Table containing that variableto be removed. The associated SGTs are alsoremoved from the SGT Table but remain in the SymbolTable. The addresses in the string of the SGTsin the Symbol Table also remain.If a statement is encountered containing a subscriptexpression and having a statement number that isreferenced by some other statement, the entire SubscriptExpression Table is cleared and all subscripts,90