What is a "tight loop"?

Solution 1:

From Wiktionary:

1. (computing) In assembly languages, a loop which contains few instructions and iterates many times.
2. (computing) Such a loop which heavily uses I/O or processing resources, failing to adequately share them with other programs running in the operating system.

For case 1 it is probably like

for (unsigned int i = 0; i < 0xffffffff; ++ i) {}

Solution 2:

I think the phrase is generally used to designate a loop which iterates many times, and which can have a serious effect on the program's performance - that is, it can use a lot of CPU cycles. Usually you would hear this phrase in a discussion of optimization.

For examples, I think of gaming, where a loop might need to process every pixel on the screen, or scientific app, where a loop is processing entries in giant arrays of data points.

Solution 3:

A tight loop is one which is CPU cache-friendly. It is a loop which fits in the instruction cache, which does no branching, and which effectively hides memory fetch latency for data being processed.