[PATCH] printf: use %ll instead of %j

[PATCH] printf: use %ll instead of %j

[Roy]

MSYS libc does not support %j[dXx] format, only %ll[dXx] is supported.

diff --git a/src/bltin/printf.c b/src/bltin/printf.c
index 893295c..12ce660 100644
--- a/src/bltin/printf.c
+++ b/src/bltin/printf.c
@@ -319,11 +319,12 @@ mklong(const char *str, const char *ch)
         char *copy;
         size_t len;

-       len = ch - str + 3;
+       len = ch - str + 4;
         STARTSTACKSTR(copy);
         copy = makestrspace(len, copy);
-       memcpy(copy, str, len - 3);
-       copy[len - 3] = 'j';
+       memcpy(copy, str, len - 4);
+       copy[len - 4] = 'l';
+       copy[len - 3] = 'l';
         copy[len - 2] = *ch;
         copy[len - 1] = '\0';
         return (copy);

Re: [PATCH] printf: use %ll instead of %j

[Jonathan Nieder]

Hi Roy,

Roy wrote:

> MSYS libc does not support %j[dXx] format, only %ll[dXx] is supported.

Are you sure that using the 'll' modifier here is more portable
than 'j'?

FWIW there was a patch posted to use PRIdMAX before, which would be a
more conservative thing to do and I think should work well.

  http://thread.gmane.org/gmane.comp.shells.dash/564/focus=605

Hope that helps,
Jonathan

Re: [PATCH] printf: use %ll instead of %j

[Harald van Dijk]

[-- Attachment #1: Type: text/plain, Size: 1773 bytes --]

On 12/03/2012 05:59 PM, Harald van Dijk wrote:
> On 12/03/2012 08:42 AM, Roy wrote:
>> MSYS libc does not support %j[dXx] format, only %ll[dXx] is supported.
>>
>> diff --git a/src/bltin/printf.c b/src/bltin/printf.c
>> index 893295c..12ce660 100644
>> --- a/src/bltin/printf.c
>> +++ b/src/bltin/printf.c
>> @@ -319,11 +319,12 @@ mklong(const char *str, const char *ch)
>>         char *copy;
>>         size_t len;
>>
>> -       len = ch - str + 3;
>> +       len = ch - str + 4;
>>         STARTSTACKSTR(copy);
>>         copy = makestrspace(len, copy);
>> -       memcpy(copy, str, len - 3);
>> -       copy[len - 3] = 'j';
>> +       memcpy(copy, str, len - 4);
>> +       copy[len - 4] = 'l';
>> +       copy[len - 3] = 'l';
>>         copy[len - 2] = *ch;
>>         copy[len - 1] = '\0';
>>         return (copy);
> 
> The calling code uses the result to print intmax_t and uintmax_t values.
> Printing intmax_t values with %lld is wrong, this will only work if
> intmax_t is really a typedef for long long (which may be true on your
> system, but is not required by the standard).
> 
> The other patch that Jonathan linked to should work just fine.

Here's a slightly tweaked version of that patch. Regardless of whether
PRIdMAX is defined as "jd" or as "lld", the use of memcpy here, first
copying "jd"/"lld" and the null byte, and only changing the 'd' after
that, surprisingly results in slightly shorter object code than the
original byte-by-byte approach, even though memcpy is fully inlined.
Perhaps that could be a reason for applying this, even if the original
reason for it, making the code work on not-quite-conforming systems,
isn't good enough to get it in dash.

Tested with normal glibc, and with glibc hacked to not provide PRIdMAX.

Cheers,
Harald

[-- Attachment #2: printf-PRIdMAX.patch --]
[-- Type: text/x-patch, Size: 875 bytes --]

diff --git a/src/bltin/printf.c b/src/bltin/printf.c
index 893295c..5f9e81c 100644
--- a/src/bltin/printf.c
+++ b/src/bltin/printf.c
@@ -316,16 +316,24 @@ out:
 static char *
 mklong(const char *str, const char *ch)
 {
+	/*
+	 * Replace a string like "%92.3u" with "%92.3"PRIuMAX.
+	 *
+	 * Although C99 does not guarantee it, we assume PRIiMAX,
+	 * PRIoMAX, PRIuMAX, PRIxMAX, and PRIXMAX are all the same
+	 * as PRIdMAX with the final 'd' replaced by the corresponding
+	 * character.
+	 */
+
 	char *copy;
 	size_t len;	
 
-	len = ch - str + 3;
+	len = ch - str + sizeof(PRIdMAX);
 	STARTSTACKSTR(copy);
 	copy = makestrspace(len, copy);
-	memcpy(copy, str, len - 3);
-	copy[len - 3] = 'j';
+	memcpy(copy, str, len - sizeof(PRIdMAX));
+	memcpy(copy + len - sizeof(PRIdMAX), PRIdMAX, sizeof(PRIdMAX));
 	copy[len - 2] = *ch;
-	copy[len - 1] = '\0';
 	return (copy);	
 }
 

Re: [PATCH] printf: use %ll instead of %j

[Jonathan Nieder]

Harald van Dijk wrote:

> Here's a slightly tweaked version of that patch.

This is easier on the eyes than the version I sent, anyway. :)

For what it's worth,
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>

Re: [PATCH] printf: use %ll instead of %j

[Herbert Xu]

On Tue, Dec 04, 2012 at 06:38:24AM +0000, Jonathan Nieder wrote:
> Harald van Dijk wrote:
> 
> > Here's a slightly tweaked version of that patch.
> 
> This is easier on the eyes than the version I sent, anyway. :)
> 
> For what it's worth,
> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>

Patch applied.  Thanks!
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt