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Fix intset-subtract to reliably produce empty-intset

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* module/language/cps/intset.scm (intset-subtract): Reliably produce
  empty-intset if the result is empty.
This commit is contained in:
Andy Wingo 2015-07-13 11:03:00 +02:00
parent 47a4727b78
commit dc27708f0b
1 changed files with 5 additions and 3 deletions
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8
module/language/cps/intset.scm
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@ -646,10 +646,10 @@
(else (make-intset/prune a-min a-shift root)))))))))
(define (intset-subtract a b)
(define tmp (new-leaf))
;; Intersect leaves.
(define (subtract-leaves a b)
(logand a (lognot b)))
(let ((out (logand a (lognot b))))
(if (zero? out) #f out)))
;; Subtract B from A starting at index I; the result will be fresh.
(define (subtract-branches/fresh shift a b i fresh)
(let lp ((i 0))
@ -721,7 +721,9 @@
(new (lp a-min a-shift old)))
(if (eq? old new)
a-root
(clone-branch-and-set a-root a-idx new)))))))))))
(let ((root (clone-branch-and-set a-root a-idx new)))
(and (or new (not (branch-empty? root)))
root))))))))))))
(define (bitvector->intset bv)
(define (finish-tail out min tail)