Adverbs - do they still exist? [duplicate]

Fast is an adjective, and an adverb as well. — ODO

adjective 1. Moving or capable of moving at high speed
"a fast and powerful car"

adverb 1. At high speed
"he was driving too fast"

Adverbs that don't use the normal -ly suffix are called flat adverbs. — Wikipedia

A flat adverb is an adverb that assumes the form of a related adjective, most often when words ending in -ly are used without the -ly. Though once quite common, flat adverbs have been largely phased out by their -ly counterparts. This shift owes to 18th-century grammarians who insisted that adverbs end in -ly. Nonetheless, flat adverbs are preferred in some idioms, as in "take it easy" and "sleep tight".

Mark Nichol of Daily Writing Tips lists some flat adverbs: bright, clean, close, deep, far, fast, flat, hard, kind, quick, right, sharp, slow, soon, and tough.