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CONDITION CODE Facility

IP.com Disclosure Number: IPCOM000062660D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Brady, JT: AUTHOR

Abstract

The result of logical computations are often expressed in terms of a condition code. It is sometimes necessary to write programs that remember the state of a condition code by altering the flow of a program. This is done because there is no easy way to combine various condition codes from numerous computations and do one branch when the logical expression has been completely computed. Additionally, this program flow alteration precludes the computation of subsequent steps in the logical expression unless the processor has the capability to make tentative calculations which may be discarded if not needed. The CONDITION CODE is set by operators which have a MOD field that is not of the form X000 (NEVER - see below). The code is set to zero at the beginning of a logical iteration of a BEGIN/END pair.

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CONDITION CODE Facility

The result of logical computations are often expressed in terms of a condition code. It is sometimes necessary to write programs that remember the state of a condition code by altering the flow of a program. This is done because there is no easy way to combine various condition codes from numerous computations and do one branch when the logical expression has been completely computed.

Additionally, this program flow alteration precludes the computation of subsequent steps in the logical expression unless the processor has the capability to make tentative calculations which may be discarded if not needed. The CONDITION CODE is set by operators which have a MOD field that is not of the form X000 (NEVER - see below).

The code is set to zero at the beginning of a logical iteration of a BEGIN/END pair. The CONDITION CODE is maintained in a condition register. All instructions that can produce a result that is testable by a conditional branch are extended to contain two new fields, MOD and CC, as shown below.

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MOD specifies which condition satisfies a logical computation and how to generate the condition code. If an operator is not involved in the logical expression a MOD of ALWAYS should be used. If MOD is not 111 or 000, the condition code generated is 010 if the result of the operations corresponds to the MOD field; otherwise, a 101 is generated for the condition code. If MOD is 000, a condition code of 000 is generated. If MOD is 111, a condition code corresponding to the...