Browse Prior Art Database

Loop Instruction

IP.com Disclosure Number: IPCOM000076400D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Bergeman, R: AUTHOR [+3]

Abstract

The LOOP function is a multifield instruction modifier to control iterative sequencing through a short segment of code.

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Loop Instruction

The LOOP function is a multifield instruction modifier to control iterative sequencing through a short segment of code.

Essentially the LOOP incorporates both Branch on Condition and Branch on Count in the code sequence implicitly rather than explicitly. This implicit incorporation should produce substantial performance gains for iterative processes, in addition to the improved performance through forced instruction buffering and loop recognition in pipeline organizations.

The LOOP instruction fields specify loop length, instruction tag, branch condition, effective address, and index register.

The instruction tag indicates which instruction in the loop is to be followed in each iteration by an examination of the condition code. When the branch condition matches the condition code, a branch is taken to the location pointed to by the effective address specified in the LOOP instruction. (analogous to Branch on Condition).

The index register is automatically decremented at the conclusion of each iteration through the loop. If the decrementing results in zero contents, the loop is terminated and normal instruction sequencing proceeds.

The LOOP is interruptible only at the conclusion of each iteration and after index decrementing and testing. The Instruction Counter upon interrupt will be pointing to the LOOP instruction, so that upon resumption of the interrupted routine the LOOP is directly resumed.

In an architecture providing index and delta fields...