(inst sll bytes (- n-widetag-bits 2) header)
(inst lda header (+ (ash -2 n-widetag-bits) type) header)
(inst srl bytes n-lowtag-bits bytes)
(inst sll bytes (- n-widetag-bits 2) header)
(inst lda header (+ (ash -2 n-widetag-bits) type) header)
(inst srl bytes n-lowtag-bits bytes)