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change real->decimal-string (PR 9285)

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svn: r9210
This commit is contained in:
Matthew Flatt 2008-04-08 21:56:29 +00:00
parent 021d4d7527
commit cb3fdd8fc5
2 changed files with 26 additions and 22 deletions
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27
collects/scheme/private/string.ss
View File

@ -15,18 +15,21 @@
(define (real->decimal-string n [digits 2])
(unless (exact-nonnegative-integer? digits)
(raise-type-error 'real->decimal-string "exact-nonnegative-integer" n))
(if (zero? digits)
(number->string (inexact->exact (round n)))
(let* ([e (expt 10 digits)]
[num (round (abs (* e (inexact->exact n))))])
(format "~a~a.~a"
(if (negative? n) "-" "")
(quotient num e)
(let ([s (number->string (remainder num e))])
(if (= (string-length s) digits)
s
(string-append (make-string (- digits (string-length s)) #\0)
s)))))))
(let* ([e (expt 10 digits)]
[num (round (abs (* e (inexact->exact n))))])
(format "~a~a.~a"
(if (or (negative? n)
(equal? n -0.0))
"-"
"")
(quotient num e)
(if (zero? digits)
""
(let ([s (number->string (remainder num e))])
(if (= (string-length s) digits)
s
(string-append (make-string (- digits (string-length s)) #\0)
s)))))))
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Regexp helpers

21
collects/tests/mzscheme/string.ss
View File

@ -5,20 +5,21 @@
;; to add when this library is there: (require scheme/string)
(test "0" real->decimal-string 0 0)
(test "0" real->decimal-string 0.0 0)
(test "1" real->decimal-string 0.6 0)
(test "1" real->decimal-string 3/4 0)
(test "1" real->decimal-string 1.2 0)
(test "0" real->decimal-string -0.0 0) ; note this!
(test "0.00" real->decimal-string -0.0) ; same here...
(test "-1" real->decimal-string -0.6 0)
(test "-1" real->decimal-string -3/4 0)
(test "-1" real->decimal-string -1.2 0)
(test "0." real->decimal-string 0 0)
(test "0." real->decimal-string 0.0 0)
(test "1." real->decimal-string 0.6 0)
(test "1." real->decimal-string 3/4 0)
(test "1." real->decimal-string 1.2 0)
(test "-0." real->decimal-string -0.0 0) ; note this!
(test "-0.00" real->decimal-string -0.0) ; same here...
(test "-1." real->decimal-string -0.6 0)
(test "-1." real->decimal-string -3/4 0)
(test "-1." real->decimal-string -1.2 0)
(test "1.20" real->decimal-string 1.2)
(test "-1.20" real->decimal-string -1.2)
(test "1.00" real->decimal-string 0.99999999999)
(test "-1.00" real->decimal-string -0.99999999999)
(test "1999999999999999859514578049071102439861518336.00" real->decimal-string 2e45)
(let ([s (list->string
(let loop ([i 0])