42 lines
1.2 KiB
Racket
42 lines
1.2 KiB
Racket
#lang racket
|
|
(require racket/unsafe/ops
|
|
(for-syntax racket/fixnum racket/vector))
|
|
(provide fxpopcount)
|
|
;; Count set bits for 30 bit number in 5 steps.
|
|
;; for 62 bit number in 6.
|
|
|
|
(define-for-syntax lut
|
|
#(#x2AAAAAAA
|
|
#x0CCCCCCC
|
|
#x30F0F0F0
|
|
#x3F00FF00
|
|
#x3FFF0000))
|
|
|
|
(define-for-syntax lut62
|
|
#(#x2AAAAAAAAAAAAAAA
|
|
#x0CCCCCCCCCCCCCCC
|
|
#x30F0F0F0F0F0F0F0
|
|
#x3F00FF00FF00FF00
|
|
#x3FFF0000FFFF0000
|
|
#x3FFFFFFF00000000))
|
|
|
|
(define-syntax (mk-fxpopcount stx)
|
|
(syntax-case stx ()
|
|
[(_ name)
|
|
;; Choose at compile time what word length is
|
|
(let* ([lut (if (fixnum? (expt 2 61)) lut62 lut)]
|
|
[flut (vector-map bitwise-not lut)])
|
|
;; Unroll the addition loop
|
|
#`(define (name n)
|
|
(unless (fixnum? n) (raise-argument-error 'name "fixnum?" 0 n))
|
|
(let* #,(for/list ([m (in-vector lut)]
|
|
[f (in-vector flut)]
|
|
[b (in-naturals)])
|
|
#`[n (unsafe-fx+ (unsafe-fxrshift (unsafe-fxand n #,m)
|
|
#,(fxlshift 1 b))
|
|
(unsafe-fxand n #,f))])
|
|
n)))]))
|
|
|
|
(mk-fxpopcount fxpopcount)
|
|
|