* bug#24630: guile-2.0.12: Comparison is always true warning - may cause problems.
@ 2016-10-06 20:49 Jens Bauer
2017-03-01 9:18 ` Andy Wingo
0 siblings, 1 reply; 3+ messages in thread
From: Jens Bauer @ 2016-10-06 20:49 UTC (permalink / raw)
To: 24630
I get the following warnings, when building on Mac OS X.
(It should show up for all platforms, though):
In file included from /Users/jens/open-source/Source/guile-2.0.12/libguile/numbers.c:9731:
/Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c: In function 'scm_to_int8':
/Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
/Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
In file included from /Users/jens/open-source/Source/guile-2.0.12/libguile/numbers.c:9747:
/Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c: In function 'scm_to_int16':
/Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
/Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
Notice that it's only from line 94, which reads...
if (n >= TYPE_MIN && n <= TYPE_MAX)
... looking at the top of the file, it says: "It is only for signed types", so I look in ...
numbers.c:9731
numbers.c:9747
... which is int8 and int16 (signed integers); this should be as intended.
The variable 'n' is declared as scm_t_signed_bits, which is a scm_t_intptr, which is an intptr_t, which is just a 'long'.
So my guess is that the problem must be with TYPE_MIN and TYPE_MAX.
In numbers.c, line 9742, they're defined as follows:
#define TYPE scm_t_int16
#define TYPE_MIN SCM_T_INT16_MIN
#define TYPE_MAX SCM_T_INT16_MAX
... looks good to me, but where's the definition of SCM_T_INT16_MIN and SCM_T_INT16_MAX ?
-It seems to be in __scm.h:
#define SCM_I_UTYPE_MAX(type) ((type)-1)
#define SCM_I_TYPE_MAX(type,umax) ((type)((umax)/2))
#define SCM_I_TYPE_MIN(type,umax) (-((type)((umax)/2))-1)
#define SCM_T_UINT8_MAX SCM_I_UTYPE_MAX(scm_t_uint8)
#define SCM_T_INT8_MIN SCM_I_TYPE_MIN(scm_t_int8,SCM_T_UINT8_MAX)
#define SCM_T_INT8_MAX SCM_I_TYPE_MAX(scm_t_int8,SCM_T_UINT8_MAX)
#define SCM_T_UINT16_MAX SCM_I_UTYPE_MAX(scm_t_uint16)
#define SCM_T_INT16_MIN SCM_I_TYPE_MIN(scm_t_int16,SCM_T_UINT16_MAX)
#define SCM_T_INT16_MAX SCM_I_TYPE_MAX(scm_t_int16,SCM_T_UINT16_MAX)
Now, this is where things get interesting. The macros are cool, but I think the use seems to be incorrect.
Let's try an example (SCM_T_INT16_MIN):
SCM_T_INT16_MIN = SCM_I_TYPE_MIN(scm_t_int16,SCM_T_UINT16_MAX)
Expands to ...
SCM_T_INT16_MIN = (-((scm_t_int16)((-1)/2))-1)
... which can be cleaned up ...
SCM_T_INT16_MIN = (-(((-1)/2))-1)
A signed integer of value -1 divided by 2, is the same as bitshifting to the right by using ASR; the result will be -1.
SCM_T_INT16_MIN = (-(((-1)))-1)
SCM_T_INT16_MIN = (-((-1))-1)
SCM_T_INT16_MIN = (-(-1)-1)
SCM_T_INT16_MIN = (+1-1)
SCM_T_INT16_MIN = (0)
... Ehm ... Did I do something wrong ?
I expected the value -32768, but got 0.
Wouldn't it be correct to typecast as scm_t_uint16 instead of scm_t_int16 (and thus scm_t_uint8 instead of scm_t_int8) ?
Love
Jens
^ permalink raw reply [flat|nested] 3+ messages in thread
* bug#24630: guile-2.0.12: Comparison is always true warning - may cause problems.
2016-10-06 20:49 bug#24630: guile-2.0.12: Comparison is always true warning - may cause problems Jens Bauer
@ 2017-03-01 9:18 ` Andy Wingo
2017-03-01 11:34 ` Jens Bauer
0 siblings, 1 reply; 3+ messages in thread
From: Andy Wingo @ 2017-03-01 9:18 UTC (permalink / raw)
To: Jens Bauer; +Cc: 24630-done
Hi,
On Thu 06 Oct 2016 22:49, Jens Bauer <jens-guile-bug@plustv.dk> writes:
> I get the following warnings, when building on Mac OS X.
> (It should show up for all platforms, though):
>
> In file included from /Users/jens/open-source/Source/guile-2.0.12/libguile/numbers.c:9731:
> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c: In function 'scm_to_int8':
> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
These are not really bugs. I mean, we shouldn't produce warnings, but
GCC doesn't warn on these, so clearly there is a heuristic which clang
has set differently; but the actual code is fine.
In your investigations below there are some errors. I include a couple
of inline comments for your enjoyment.
> In file included from /Users/jens/open-source/Source/guile-2.0.12/libguile/numbers.c:9747:
> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c: In function 'scm_to_int16':
> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94: warning: comparison is always true due to limited range of data type
>
> Notice that it's only from line 94, which reads...
> if (n >= TYPE_MIN && n <= TYPE_MAX)
>
> ... looking at the top of the file, it says: "It is only for signed types", so I look in ...
>
> numbers.c:9731
> numbers.c:9747
> ... which is int8 and int16 (signed integers); this should be as intended.
>
> The variable 'n' is declared as scm_t_signed_bits, which is a scm_t_intptr, which is an intptr_t, which is just a 'long'.
>
> So my guess is that the problem must be with TYPE_MIN and TYPE_MAX.
>
> In numbers.c, line 9742, they're defined as follows:
> #define TYPE scm_t_int16
> #define TYPE_MIN SCM_T_INT16_MIN
> #define TYPE_MAX SCM_T_INT16_MAX
>
> ... looks good to me, but where's the definition of SCM_T_INT16_MIN and SCM_T_INT16_MAX ?
> -It seems to be in __scm.h:
>
> #define SCM_I_UTYPE_MAX(type) ((type)-1)
> #define SCM_I_TYPE_MAX(type,umax) ((type)((umax)/2))
> #define SCM_I_TYPE_MIN(type,umax) (-((type)((umax)/2))-1)
>
> #define SCM_T_UINT8_MAX SCM_I_UTYPE_MAX(scm_t_uint8)
> #define SCM_T_INT8_MIN SCM_I_TYPE_MIN(scm_t_int8,SCM_T_UINT8_MAX)
> #define SCM_T_INT8_MAX SCM_I_TYPE_MAX(scm_t_int8,SCM_T_UINT8_MAX)
>
> #define SCM_T_UINT16_MAX SCM_I_UTYPE_MAX(scm_t_uint16)
> #define SCM_T_INT16_MIN SCM_I_TYPE_MIN(scm_t_int16,SCM_T_UINT16_MAX)
> #define SCM_T_INT16_MAX SCM_I_TYPE_MAX(scm_t_int16,SCM_T_UINT16_MAX)
>
> Now, this is where things get interesting. The macros are cool, but I think the use seems to be incorrect.
>
> Let's try an example (SCM_T_INT16_MIN):
> SCM_T_INT16_MIN = SCM_I_TYPE_MIN(scm_t_int16,SCM_T_UINT16_MAX)
> Expands to ...
> SCM_T_INT16_MIN = (-((scm_t_int16)((-1)/2))-1)
SCM_T_UINT16_MAX expands to ((scm_t_uint16)-1) which expands to the
uint16_t value 0xffff. (These intermediate expansions have type in
addition to value.) SCM_T_INT16_MIN is -(0xffff/2)-1, which is
(int16_t)-0x8000.
> ... which can be cleaned up ...
>
> SCM_T_INT16_MIN = (-(((-1)/2))-1)
>
> A signed integer of value -1 divided by 2, is the same as bitshifting to the right by using ASR; the result will be -1.
>
> SCM_T_INT16_MIN = (-(((-1)))-1)
> SCM_T_INT16_MIN = (-((-1))-1)
> SCM_T_INT16_MIN = (-(-1)-1)
> SCM_T_INT16_MIN = (+1-1)
> SCM_T_INT16_MIN = (0)
>
> ... Ehm ... Did I do something wrong ?
> I expected the value -32768, but got 0.
>
> Wouldn't it be correct to typecast as scm_t_uint16 instead of scm_t_int16 (and thus scm_t_uint8 instead of scm_t_int8) ?
>
Happy hacking,
Andy
^ permalink raw reply [flat|nested] 3+ messages in thread
* bug#24630: guile-2.0.12: Comparison is always true warning - may cause problems.
2017-03-01 9:18 ` Andy Wingo
@ 2017-03-01 11:34 ` Jens Bauer
0 siblings, 0 replies; 3+ messages in thread
From: Jens Bauer @ 2017-03-01 11:34 UTC (permalink / raw)
To: Andy Wingo; +Cc: 24630-done, Jens Bauer
Hi Andy.
Thanks for looking into this.
Your reply is correct and I can see that I made an error when manually reducing the expression.
FIY: The warning shows up in GCC-4.2.1, not clang (I cannot run clang on any of my Macs, they're PowerPC based).
-So the warning does show up when buiding using GCC-4.2.1.
Love
Jens
On Wed, 01 Mar 2017 10:18:28 +0100, Andy Wingo wrote:
> Hi,
>
> On Thu 06 Oct 2016 22:49, Jens Bauer <jens-guile-bug@plustv.dk> writes:
>
>> I get the following warnings, when building on Mac OS X.
>> (It should show up for all platforms, though):
>>
>> In file included from
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/numbers.c:9731:
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:
>> In function 'scm_to_int8':
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94:
>> warning: comparison is always true due to limited range of data type
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94:
>> warning: comparison is always true due to limited range of data type
>
> These are not really bugs. I mean, we shouldn't produce warnings, but
> GCC doesn't warn on these, so clearly there is a heuristic which clang
> has set differently; but the actual code is fine.
>
> In your investigations below there are some errors. I include a couple
> of inline comments for your enjoyment.
>
>> In file included from
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/numbers.c:9747:
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:
>> In function 'scm_to_int16':
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94:
>> warning: comparison is always true due to limited range of data type
>> /Users/jens/open-source/Source/guile-2.0.12/libguile/conv-integer.i.c:94:
>> warning: comparison is always true due to limited range of data type
>>
>> Notice that it's only from line 94, which reads...
>> if (n >= TYPE_MIN && n <= TYPE_MAX)
>>
>> ... looking at the top of the file, it says: "It is only for signed
>> types", so I look in ...
>>
>> numbers.c:9731
>> numbers.c:9747
>> ... which is int8 and int16 (signed integers); this should be as intended.
>>
>> The variable 'n' is declared as scm_t_signed_bits, which is a
>> scm_t_intptr, which is an intptr_t, which is just a 'long'.
>>
>> So my guess is that the problem must be with TYPE_MIN and TYPE_MAX.
>>
>> In numbers.c, line 9742, they're defined as follows:
>> #define TYPE scm_t_int16
>> #define TYPE_MIN SCM_T_INT16_MIN
>> #define TYPE_MAX SCM_T_INT16_MAX
>>
>> ... looks good to me, but where's the definition of SCM_T_INT16_MIN
>> and SCM_T_INT16_MAX ?
>> -It seems to be in __scm.h:
>>
>> #define SCM_I_UTYPE_MAX(type) ((type)-1)
>> #define SCM_I_TYPE_MAX(type,umax) ((type)((umax)/2))
>> #define SCM_I_TYPE_MIN(type,umax) (-((type)((umax)/2))-1)
>>
>> #define SCM_T_UINT8_MAX SCM_I_UTYPE_MAX(scm_t_uint8)
>> #define SCM_T_INT8_MIN SCM_I_TYPE_MIN(scm_t_int8,SCM_T_UINT8_MAX)
>> #define SCM_T_INT8_MAX SCM_I_TYPE_MAX(scm_t_int8,SCM_T_UINT8_MAX)
>>
>> #define SCM_T_UINT16_MAX SCM_I_UTYPE_MAX(scm_t_uint16)
>> #define SCM_T_INT16_MIN SCM_I_TYPE_MIN(scm_t_int16,SCM_T_UINT16_MAX)
>> #define SCM_T_INT16_MAX SCM_I_TYPE_MAX(scm_t_int16,SCM_T_UINT16_MAX)
>>
>> Now, this is where things get interesting. The macros are cool, but
>> I think the use seems to be incorrect.
>>
>> Let's try an example (SCM_T_INT16_MIN):
>> SCM_T_INT16_MIN = SCM_I_TYPE_MIN(scm_t_int16,SCM_T_UINT16_MAX)
>> Expands to ...
>> SCM_T_INT16_MIN = (-((scm_t_int16)((-1)/2))-1)
>
> SCM_T_UINT16_MAX expands to ((scm_t_uint16)-1) which expands to the
> uint16_t value 0xffff. (These intermediate expansions have type in
> addition to value.) SCM_T_INT16_MIN is -(0xffff/2)-1, which is
> (int16_t)-0x8000.
>
>> ... which can be cleaned up ...
>>
>> SCM_T_INT16_MIN = (-(((-1)/2))-1)
>>
>> A signed integer of value -1 divided by 2, is the same as
>> bitshifting to the right by using ASR; the result will be -1.
>>
>> SCM_T_INT16_MIN = (-(((-1)))-1)
>> SCM_T_INT16_MIN = (-((-1))-1)
>> SCM_T_INT16_MIN = (-(-1)-1)
>> SCM_T_INT16_MIN = (+1-1)
>> SCM_T_INT16_MIN = (0)
>>
>> ... Ehm ... Did I do something wrong ?
>> I expected the value -32768, but got 0.
>>
>> Wouldn't it be correct to typecast as scm_t_uint16 instead of
>> scm_t_int16 (and thus scm_t_uint8 instead of scm_t_int8) ?
>>
>
> Happy hacking,
>
> Andy
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-03-01 11:34 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-10-06 20:49 bug#24630: guile-2.0.12: Comparison is always true warning - may cause problems Jens Bauer
2017-03-01 9:18 ` Andy Wingo
2017-03-01 11:34 ` Jens Bauer
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).