> On Dec 31, 2016, at 12:05 PM, Robby Findler <ro...@eecs.northwestern.edu>
> wrote:
>
> But this introduces an additional cost that's a little bit more
> troublesome to measure. Specifically, each namespace that instantiates
> `racket/base` will now take a tiny bit more space and take a tiny bit
> longer to initialize.
> As one data point, here's a histogram of the 20k or so calls to
> number->string that happen during the start up of DrRacket (first
> entry in each list is the argument passed to number->string and the
> second is the number of times that call happened)
Hmm, well if the distribution of inputs is that imbalanced, perhaps this is the
better cheat:
; 100,000 conversions of 100 random integers < 123
cpu time: 779 real time: 791 gc time: 16 ; number->string
cpu time: 769 real time: 771 gc time: 13 ; number->string**
; 100,000 conversions of 100 random integers < 123456
cpu time: 1365 real time: 1384 gc time: 22 ; number->string
cpu time: 941 real time: 955 gc time: 13 ; number->string**
; 100,000 conversions of 100 random integers < 123456789
cpu time: 1891 real time: 1904 gc time: 26 ; number->string
cpu time: 963 real time: 979 gc time: 17 ; number->string**
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
#lang racket
(define number->string**
(let ([digits (list->vector (string->list "0123456789"))]
[cache (make-hasheqv)])
(λ (N)
(hash-ref! cache N
(λ ()
(list->string
(let loop ([N N][acc empty])
(define q (quotient N 10))
(define next-acc (cons (vector-ref digits (remainder N
10)) acc))
(if (zero? q)
next-acc
(loop q next-acc)))))))))
(define-syntax-rule (test-it id ...)
(begin
(module+ test
(require rackunit)
(check-equal? (id 1234567890987654321)
(number->string 1234567890987654321))
(for ([x (in-range 10000)])
(check-equal? (id x )
(number->string x)))) ...))
(test-it number->string**)
(define iterations 100000)
(define-syntax-rule (time-it number-to-convert id ...)
(begin
(define numbers (for/list ([i (in-range 100)])
(random number-to-convert)))
(begin
(collect-garbage)
(time
(for* ([x (in-range iterations)]
[n (in-list numbers)])
(id n)))) ...))
(time-it 123 number->string number->string**)
(time-it 123456 number->string number->string**)
(time-it 123456789 number->string number->string**)
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