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The condition/expression is evaluated, and if the condition/expression is true, [1] the code within all of their following in the block is executed. This repeats until the condition/expression becomes false. Because the while loop checks the condition/expression before the block is executed, the control structure is often also known as a pre ...
A conditional loop has the potential to become an infinite loop when nothing in the loop's body can affect the outcome of the loop's conditional statement. However, infinite loops can sometimes be used purposely, often with an exit from the loop built into the loop implementation for every computer language , but many share the same basic ...
If xxx1 is omitted, we get a loop with the test at the top (a traditional while loop). If xxx2 is omitted, we get a loop with the test at the bottom, equivalent to a do while loop in many languages. If while is omitted, we get an infinite loop. The construction here can be thought of as a do loop with the while check in the middle. Hence this ...
Do while loops check the condition after the block of code is executed. This control structure can be known as a post-test loop. This means the do-while loop is an exit-condition loop. However a while loop will test the condition before the code within the block is executed.
/* precondition: x 2 = 0 */ LOOP x 1 DO x 0 := 0; LOOP x 2 DO x 0 := x 0 + 1 END; x 2 := x 2 + 1 END. This program can be used as a subroutine in other LOOP programs. The LOOP syntax can be extended with the following statement, equivalent to calling the above as a subroutine: x 0 := x 1 ∸ 1 Remark: Again one has to mind the side effects.
ALGOL 68 has what was considered the universal loop, the full syntax is: FOR i FROM 1 BY 2 TO 3 WHILE i≠4 DO ~ OD Further, the single iteration range could be replaced by a list of such ranges. There are several unusual aspects of the construct only the do ~ od portion was compulsory, in which case the loop will iterate indefinitely.
The loop is: reinforcing if, after going around the loop, one ends up with the same result as the initial assumption. balancing if the result contradicts the initial assumption. Or to put it in other words: reinforcing loops have an even number of negative links (zero also is even, see example below) balancing loops have an odd number of ...
Chapter 7, pages 8 to 10, of Michael Abrash's Graphics Programming Black Book is about loop unrolling, with an example in x86 assembly. Generalized Loop Unrolling, gives a concise introduction. Optimizing subroutines in assembly language Agner Fog's optimizations handbook with the loop unrolling technique (2012).