From: Andy Moreton <andrewjmoreton@gmail.com>
To: emacs-devel@gnu.org
Subject: Re: Merging bignum to master
Date: Tue, 14 Aug 2018 01:21:51 +0100 [thread overview]
Message-ID: <86r2j13ihs.fsf@gmail.com> (raw)
In-Reply-To: 87a7prk0h6.fsf@tromey.com
On Sun 12 Aug 2018, Tom Tromey wrote:
>>>>>> "Basil" == Basil L Contovounesios <contovob@tcd.ie> writes:
>
> Basil> It'd be nice if expt could be updated to handle bignums:
>
> What do you think of this?
>
> Tom
>
> diff --git a/src/floatfns.c b/src/floatfns.c
> index bbf7df4db3..c55418a35c 100644
> --- a/src/floatfns.c
> +++ b/src/floatfns.c
> @@ -206,25 +206,28 @@ DEFUN ("expt", Fexpt, Sexpt, 2, 2, 0,
> {
> CHECK_FIXNUM_OR_FLOAT (arg1);
> CHECK_FIXNUM_OR_FLOAT (arg2);
> - if (FIXNUMP (arg1) /* common lisp spec */
> + if (INTEGERP (arg1) /* common lisp spec */
> && FIXNUMP (arg2) /* don't promote, if both are ints, and */
> && XFIXNUM (arg2) >= 0) /* we are sure the result is not fractional */
> { /* this can be improved by pre-calculating */
> - EMACS_INT y; /* some binary powers of x then accumulating */
> - EMACS_UINT acc, x; /* Unsigned so that overflow is well defined. */
You have dropped some of the commentary that explains how it is trying
to give similar behaviour to Common Lisp. See the description at:
<http://www.lispworks.com/documentation/lw50/CLHS/Body/f_exp_e.htm>
> Lisp_Object val;
> + mpz_t x, *xp, r;
>
> - x = XFIXNUM (arg1);
> - y = XFIXNUM (arg2);
> - acc = (y & 1 ? x : 1);
> -
> - while ((y >>= 1) != 0)
> + if (BIGNUMP (arg1))
> + xp = &XBIGNUM (arg1)->value;
> + else
> {
> - x *= x;
> - if (y & 1)
> - acc *= x;
> + mpz_init_set_si (x, XFIXNUM (arg1));
This doesn't work for systems where sizeof (EMACS_INT) > sizeof (long).
> + xp = &x;
> }
> - XSETINT (val, acc);
> +
> + mpz_init (r);
> + mpz_pow_ui (r, *xp, XFIXNUM (arg2));
Likewise.
> +
> + val = make_number (r);
> + mpz_clear (r);
> + if (xp == &x)
> + mpz_clear (x);
> return val;
> }
> return make_float (pow (XFLOATINT (arg1), XFLOATINT (arg2)));
> diff --git a/test/src/floatfns-tests.el b/test/src/floatfns-tests.el
> index 7714c05d60..4fab032ecb 100644
> --- a/test/src/floatfns-tests.el
> +++ b/test/src/floatfns-tests.el
> @@ -46,4 +46,8 @@
> (should (= (+ (logb most-positive-fixnum) 1)
> (logb (+ most-positive-fixnum 1)))))
>
> +(ert-deftest bignum-expt ()
> + (should (= (expt 10 100)
> + (apply #'* (make-list 100 10)))))
> +
> (provide 'floatfns-tests)
next prev parent reply other threads:[~2018-08-14 0:21 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-11 19:47 Merging bignum to master Tom Tromey
2018-08-11 21:28 ` Basil L. Contovounesios
2018-08-12 16:34 ` Tom Tromey
2018-08-13 12:21 ` Basil L. Contovounesios
2018-08-14 0:21 ` Andy Moreton [this message]
2018-08-15 23:41 ` Andy Moreton
2018-08-16 15:38 ` Basil L. Contovounesios
2018-08-19 8:26 ` Paul Eggert
2018-08-17 14:58 ` Eli Zaretskii
2018-08-12 6:29 ` Ulrich Mueller
2018-08-12 8:09 ` Paul Eggert
2018-08-12 17:21 ` Ulrich Mueller
2018-08-12 18:20 ` Eli Zaretskii
2018-08-12 19:30 ` Ulrich Mueller
2018-08-13 0:15 ` Paul Eggert
2018-08-12 18:05 ` Eli Zaretskii
2018-08-12 23:53 ` Paul Eggert
2018-08-13 0:20 ` Tom Tromey
2018-08-13 7:51 ` Andreas Schwab
2018-08-13 8:06 ` Ulrich Mueller
2018-08-13 9:14 ` Paul Eggert
2018-08-14 23:09 ` Paul Eggert
2018-08-16 2:46 ` Richard Stallman
2018-08-13 23:31 ` Richard Stallman
2018-08-14 1:41 ` Paul Eggert
2018-08-16 2:41 ` Richard Stallman
2018-08-16 19:31 ` Paul Eggert
2018-08-16 22:02 ` Stefan Monnier
2018-08-12 7:37 ` John Wiegley
2018-08-12 18:21 ` Eli Zaretskii
2018-08-12 11:48 ` Pip Cet
2018-08-12 16:02 ` Tom Tromey
2018-08-13 22:58 ` Paul Eggert
2018-08-14 1:12 ` Noam Postavsky
2018-08-14 13:04 ` Pip Cet
2018-08-14 18:01 ` Paul Eggert
2018-08-15 15:20 ` Pip Cet
2018-08-15 16:17 ` Paul Eggert
2018-08-15 23:57 ` Andy Moreton
2018-08-16 22:00 ` Stefan Monnier
2018-08-20 16:28 ` Some vars now limited to fixnum size. (Was: Merging bignum to master) Karl Fogel
2018-08-20 16:54 ` Paul Eggert
2018-08-20 17:27 ` Eli Zaretskii
2018-08-20 17:27 ` Paul Eggert
2018-08-20 18:00 ` Eli Zaretskii
2018-08-20 19:55 ` Pip Cet
2018-08-20 23:15 ` Paul Eggert
2018-08-21 15:01 ` Some vars now limited to fixnum size Tom Tromey
2018-08-21 16:36 ` Andy Moreton
2018-08-21 18:46 ` Paul Eggert
2018-08-22 15:39 ` Tom Tromey
2018-08-21 3:38 ` Some vars now limited to fixnum size. (Was: Merging bignum to master) Richard Stallman
2018-08-21 4:09 ` Paul Eggert
2018-08-22 4:03 ` Richard Stallman
2018-08-22 4:53 ` Paul Eggert
2018-08-20 17:25 ` Eli Zaretskii
2018-08-14 0:51 ` Merging bignum to master Andy Moreton
2018-08-15 15:46 ` Andy Moreton
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