(a) A person convicted pursuant to section 2251 of this chapter of having, possessing, bearing, transporting, carrying or having under his proximate control a deadly or dangerous weapon as therein described during the commission or attempted commission of a crime of violence shall be incarcerated for a term of imprisonment of not less than one-half of the maximum sentence specified in that section.
(b) Notwithstanding any other provision of law, with respect to a person convicted pursuant to section 2251 of this chapter of having, possessing, bearing, transporting, carrying or having under his proximate control a deadly or dangerous weapon as therein described, during the commission or attempted commission of a crime of violence, and with respect to a person convicted pursuant to subsection (a) or (b) of section 2253 of this chapter, of having, possessing, bearing, transporting, carrying, or having under his proximate control, a firearm, machine gun or sawed-off shot gun as therein referred to, during the commission or attempted commission of a crime of violence, adjudication of guilt or imposition of sentence shall not be suspended, deferred, or withheld, nor shall such person be eligible for probation, parole, or any other form of release prior to serving the mandatory minimum term of imprisonment prescribed by subsection (a) of this section or subsection (a) or (b) of section 2253, as the case may be.