On 3/31/20 3:50 PM, Paolo Montrasi wrote:
I am asking here for an advice in improving runtime speed crunching bitwise operations on u64 integers since I have no experience using scheme and Gambit.
Looking at the documentation I see that fixnum is providing some help but I apparently u64 integers are not "compatible" with fixnum operations
> (fixnum? 18446744073709551615)
#f
Can you share suggestions for my next exercise
That may be possible using some of Gambit's low-level, internal, unsafe, very-bad-indeed routines for manipulating bignum "adigits" (for "addition digits", although they're the size used for many other things), which are 64 bits, unsigned, on 64-bit machines. (They're only 14 bits wide in the universal backend, though.)
You'll find these routines in _num.scm:
;;; Sets x[i] to x[i] & y[j] (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-and! x i y j))
;;; Sets x[i] to ~x[i] & y[j] (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-andc1! x i y j))
;;; Sets x[i] to x[i] & ~y[j] (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-andc2! x i y j))
;;; Sets x[i] to ~(x[i] ^ y[j]) (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-eqv! x i y j))
;;; Sets x[i] to x[i] | y[j] (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-ior! x i y j))
;;; Sets x[i] to ~(x[i] & y[j]) (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-nand! x i y j))
;;; Sets x[i] to ~(x[i] | y[j]) (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-nor! x i y j))
;;; Sets x[i] to !x[i] (accessing x as adigits)
(define-prim (##bignum.adigit-bitwise-not! x i))
;;; Sets x[i] to ~x[i] | y[j] (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-orc1! x i y j))
;;; Sets x[i] to x[i] | ~y[j] (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-orc2! x i y j))
;;; Sets x[i] to x[i] ^ y[j] (accessing x and y as adigits)
(define-prim (##bignum.adigit-bitwise-xor! x i y j))
There's also
(define-prim (##bignum.make k x complement?)
which makes a new bignum with k adigits, copying x if it's given, and complementing things if the last argument is #t. It may be easier to just call
(define-prim (##bignum.copy x)
(##bignum.make (##bignum.adigit-length x) x #f))
Using one of
(define ##bignum.adigit-ones (##fixnum->bignum -1)) ;; the 0th adigit is all ones
(define ##bignum.adigit-zeros (##fixnum->bignum 0)) ;; the 0th adigit is all zeros
as a starter.
Now, ##bignum.adigit-ones and ##bignum.adigit-zeros are unnormalized bignums, as could be many other results one can get by using these routines that manipulate adigits, so I wouldn't try to print them using the usual library routines, but this could get you started.
Brad