- (if (= y 1)
- ;; SHIFT-RIGHT-UNALIGNED won't do the right thing
- ;; with a shift count of 0, so special case this.
- ;; We could probably get away with (VALUES X 0)
- ;; here, but it's not clear that some of the
- ;; normalization logic further down would avoid
- ;; mutilating X. Just go ahead and cons, consing's
- ;; cheap.
- (values (copy-bignum x len-x) 0)
- (let ((n-bits (1- (integer-length y))))
- (values
- (shift-right-unaligned x 0 n-bits len-x
- ((= j res-len-1)
- (setf (%bignum-ref res j)
- (%ashr (%bignum-ref x i) n-bits))
- res)
- res)
- (logand (%bignum-ref x 0) (1- y)))))
+ ;; SHIFT-RIGHT-UNALIGNED won't do the right thing
+ ;; with a shift count of 0 or -1, so special case this.
+ (cond ((= y 0)
+ (error 'division-by-zero))
+ ((= y 1)
+ ;; We could probably get away with (VALUES X 0)
+ ;; here, but it's not clear that some of the
+ ;; normalization logic further down would avoid
+ ;; mutilating X. Just go ahead and cons, consing's
+ ;; cheap.
+ (values (copy-bignum x len-x) 0))
+ (t
+ (let ((n-bits (1- (integer-length y))))
+ (values
+ (shift-right-unaligned x 0 n-bits len-x
+ ((= j res-len-1)
+ (setf (%bignum-ref res j)
+ (%ashr (%bignum-ref x i) n-bits))
+ res)
+ res)
+ (logand (%bignum-ref x 0) (1- y))))))