<i>Most</i> languages do (though implementation bugs are common—plenty of languages where 64-bit precision is required actually end up being implemented in such a way that 80-bit precision is used on x86).<p>That said, a lot of low-level languages don&#x27;t: C doesn&#x27;t guarantee this, for example. C doesn&#x27;t even mandate IEEE 754, and it merely requires that &quot;float&quot; is a subset of the values of &quot;double&quot; which is itself a subset of the values of &quot;long double&quot;.