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* Optimized the zero case in $flonum->exact.

This commit is contained in:
Abdulaziz Ghuloum 2007-11-17 09:12:49 -05:00
parent 87d1cd5ad1
commit eef196c09d
2 changed files with 17 additions and 25 deletions
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scheme/ikarus.numerics.ss
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@ -150,7 +150,14 @@
#f)))]
[(= be 0) (if (= m 0) 0 #f)]
[else #f]))]))))
(define-syntax ctexpt
(lambda (x)
(import (ikarus))
(syntax-case x ()
[(_ n m)
(expt (syntax->datum #'n) (syntax->datum #'m))])))
(define ($flonum->exact x)
(import (ikarus))
(let ([sbe ($flonum-sbe x)])
(let ([be ($fxlogand sbe #x7FF)])
(cond
@ -163,31 +170,16 @@
;;; this really needs to get optimized.
(let-values ([(pos? be m) (flonum-parts x)])
(cond
[(<= 1 be 2046) ; normalized flonum
(* (if pos? 1 -1)
(* (+ m (expt 2 52)) (expt 2 (- be 1075))))]
[(= be 0)
(* (if pos? 1 -1)
(* m (expt 2 -1074)))]
[else #f]))])))))
;;; INCORRECT (define ($flonum->exact x)
;;; INCORRECT (let* ([x0 ($fl* x 5e-324)]
;;; INCORRECT [x1 ($fl/ x0 5e-324)])
;;; INCORRECT (cond
;;; INCORRECT [($fl= x x1) ;;; x == round(x)
;;; INCORRECT ($flonum-signed-mantissa x0)]
;;; INCORRECT [($fx= be 0) ;;; denormal
;;; INCORRECT (/ ($flonum-signed-mantissa x)
;;; INCORRECT (bitwise-arithmetic-shift-left 1 1074))]
;;; INCORRECT [else ;;; x has a fraction
;;; INCORRECT (let ([v ($flonum-signed-mantissa x)])
;;; INCORRECT (let ([bits (- 1075 be)])
;;; INCORRECT (let ([int (bitwise-arithmetic-shift-right v bits)]
;;; INCORRECT [frac
;;; INCORRECT (let ([e (bitwise-arithmetic-shift-left 1 bits)])
;;; INCORRECT (/ (bitwise-and v (- e 1)) e))])
;;; INCORRECT (+ int frac))))])))
[(= be 0) ;;; denormalized
(if (= m 0)
0
(* (if pos? 1 -1)
(/ m (ctexpt 2 1074))))]
[else ; normalized flonum
(/ (+ m (ctexpt 2 52))
(bitwise-arithmetic-shift-left
(if pos? 1 -1)
(- 1075 be)))]))])))))
(define (flnumerator x)
(unless (flonum? x)