Repeat instruction
In computer instruction set architectures, a repeat instruction is a machine language instruction which repeatedly executes another instruction a fixed number of times, or until some condition is met.
Since it is an instruction that operates on other instructions like the execute instruction, it has been classified as a meta-instruction.
Computer models
The Univac 1103 includes a repeat instruction which executes the following instruction a fixed number of times, possibly incrementing one or both of the address fields of that instruction. This compensates for the architecture's lack of index registers.The GE-600/Honeywell 6000 series supports a single-instruction repeat, a double-instruction repeat, and a linked-list repeat.
The x86 ISA, starting with the 8086, includes a series of special-purpose repeat instructions which are called "repeat string opcode prefixes" and may only be applied to a small number of string instructions. These instructions repeat an operation and decrement a counter until it is zero, or may also stop when a certain condition is met.
The Texas Instruments TMS320 digital signal processor includes an instruction for repeating a single-cycle instruction or two single-cycle instruction in parallel and an instruction for repeating a block of instructions. These use special block-repeat counter registers.
The Motorola 68010 has a single instruction repeat called "loop mode." It accelerates loops consisting of one of 33 loopable instructions and a DBcc. Two instruction opcodes are prefetched and held internally while subsequent memory read/write cycles are only generated for the data operands.