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-rw-r--r--dbinterp.scm42
1 files changed, 30 insertions, 12 deletions
diff --git a/dbinterp.scm b/dbinterp.scm
index 8ccb1df..2bd4e20 100644
--- a/dbinterp.scm
+++ b/dbinterp.scm
@@ -17,18 +17,36 @@
;promotional, or sales literature without prior written consent in
;each case.
+(require 'rev4-optional-procedures) ; list-tail
+
+;;; The procedures returned by MEMOIZE are not reentrant!
+(define (dbinterp:memoize proc k)
+ (define recent (vector->list (make-vector k '(#f))))
+ (let ((tailr (list-tail recent (+ -1 k))))
+ (lambda args
+ (define asp (assoc args recent))
+ (if asp
+ (cdr asp)
+ (let ((val (apply proc args)))
+ (set-cdr! tailr (list (cons args val)))
+ (set! tailr (cdr tailr))
+ (set! recent (cdr recent))
+ val)))))
+
;;@ This procedure works only for tables with a single primary key.
(define (interpolate-from-table table column)
- (define get (table 'get column))
- (define prev (table 'isam-prev))
+ (define get (dbinterp:memoize (table 'get column) 3))
+ (define prev (dbinterp:memoize (table 'isam-prev) 3))
(define next (table 'isam-next))
- (lambda (x)
- (let ((nxt (next x)))
- (if nxt (set! nxt (car nxt)))
- (let ((prv (prev (or nxt x))))
- (if prv (set! prv (car prv)))
- (cond ((not nxt) (get prv))
- ((not prv) (get nxt))
- (else (/ (+ (* (- x prv) (get nxt))
- (* (- nxt x) (get prv)))
- (- nxt prv))))))))
+ (dbinterp:memoize
+ (lambda (x)
+ (let ((nxt (next x)))
+ (if nxt (set! nxt (car nxt)))
+ (let ((prv (prev (or nxt x))))
+ (if prv (set! prv (car prv)))
+ (cond ((not nxt) (get prv))
+ ((not prv) (get nxt))
+ (else (/ (+ (* (- x prv) (get nxt))
+ (* (- nxt x) (get prv)))
+ (- nxt prv)))))))
+ 3))