From: Helmut Eller <eller.helmut@gmail.com>
To: Stefan Monnier <monnier@IRO.UMontreal.CA>
Cc: 5114@emacsbugs.donarmstrong.com
Subject: bug#5114: 23.1.50; (string-to-number (number-to-string most-positive-fixnum))
Date: Sat, 05 Dec 2009 13:36:41 +0100 [thread overview]
Message-ID: <m2zl5x4mxy.fsf@gmail.com> (raw)
In-Reply-To: <jwvskbr6asf.fsf-monnier+emacsbugreports@gnu.org> (Stefan Monnier's message of "Thu, 03 Dec 2009 15:52:16 -0500")
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* Stefan Monnier [2009-12-03 21:52+0100] writes:
>> (setq x (string-to-number (number-to-string most-positive-fixnum)))
>> (= most-positive-fixnum x) => nil
>
>> x is 2305843009213693440 but it should be most-positive-fixnum
>> which is 2305843009213693951.
>
>> The test
>> (= most-positive-fixnum
>> (string-to-number (number-to-string most-positive-fixnum)))
>> seems to work as expected on 32-bit machines but not so on 64 bit.
>
> Indeed, it passes through a floating point conversion, so there's only
> abour 52 bit of precesion.
Here is a patch for string-to-number to use the full fixnum range:
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[-- Attachment #2: string-to-number.patch --]
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--- data.c.~1.308.~ 2009-12-05 08:07:48.000000000 +0100
+++ data.c 2009-12-05 13:27:33.000000000 +0100
@@ -2393,23 +2393,26 @@
p++;
if (isfloat_string (p, 1) && b == 10)
- val = make_float (sign * atof (p));
- else
- {
- double v = 0;
-
- while (1)
- {
- int digit = digit_to_number (*p++, b);
- if (digit < 0)
- break;
- v = v * b + digit;
- }
-
- val = make_fixnum_or_float (sign * v);
- }
-
- return val;
+ return make_float (sign * atof (p));
+ else {
+ unsigned long u = 0;
+ while (1)
+ {
+ int digit = digit_to_number (*p++, b);
+ if (digit < 0)
+ return make_number (sign * u);
+ else if (u <= (MOST_POSITIVE_FIXNUM - digit) / b)
+ u = u * b + digit;
+ else
+ {
+ /* overflow to flonums */
+ double f = ((double)u) * b + digit;
+ while (digit = digit_to_number (*p++, b), digit >= 0)
+ f = f * b + digit;
+ return make_float (sign * f);
+ }
+ }
+ }
}
\f
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Helmut
next prev parent reply other threads:[~2009-12-05 12:36 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-03 14:36 bug#5114: 23.1.50; (string-to-number (number-to-string most-positive-fixnum)) Helmut Eller
2009-12-03 20:52 ` Stefan Monnier
2009-12-05 12:36 ` Helmut Eller [this message]
2009-12-05 14:25 ` Eli Zaretskii
2009-12-05 15:18 ` Helmut Eller
2009-12-05 16:44 ` Eli Zaretskii
2011-09-18 9:47 ` Lars Magne Ingebrigtsen
2011-09-18 10:57 ` Leo
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