From: Andrew Morton <akpm@linux-foundation.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "Jani Nikula" <jani.nikula@intel.com>,
"intel-gfx@lists.freedesktop.org"
<intel-gfx@lists.freedesktop.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"David Gow" <davidgow@google.com>,
"Christian König" <christian.koenig@amd.com>
Subject: Re: [PATCH 0/4] log2: make is_power_of_2() more generic
Date: Thu, 30 Mar 2023 15:18:46 -0700 [thread overview]
Message-ID: <20230330151846.fdbc8edbfbaa6eaddb056dc7@linux-foundation.org> (raw)
In-Reply-To: <549987e4967d45159573901d330c96a0@AcuMS.aculab.com>
On Thu, 30 Mar 2023 21:53:03 +0000 David Laight <David.Laight@ACULAB.COM> wrote:
> > But wouldn't all these issues be addressed by simply doing
> >
> > #define is_power_of_2(n) (n != 0 && ((n & (n - 1)) == 0))
> >
> > ?
> >
> > (With suitable tweaks to avoid evaluating `n' more than once)
>
> I think you need to use the 'horrid tricks' from min() to get
> a constant expression from constant inputs.
This
--- a/include/linux/log2.h~a
+++ a/include/linux/log2.h
@@ -41,11 +41,11 @@ int __ilog2_u64(u64 n)
* *not* considered a power of two.
* Return: true if @n is a power of 2, otherwise false.
*/
-static inline __attribute__((const))
-bool is_power_of_2(unsigned long n)
-{
- return (n != 0 && ((n & (n - 1)) == 0));
-}
+#define is_power_of_2(_n) \
+ ({ \
+ typeof(_n) n = (_n); \
+ n != 0 && ((n & (n - 1)) == 0); \
+ })
/**
* __roundup_pow_of_two() - round up to nearest power of two
_
worked for me in a simple test.
--- a/fs/open.c~b
+++ a/fs/open.c
@@ -1564,3 +1564,10 @@ int stream_open(struct inode *inode, str
}
EXPORT_SYMBOL(stream_open);
+
+#include <linux/log2.h>
+
+int foo(void)
+{
+ return is_power_of_2(43);
+}
_
foo:
# fs/open.c:1573: }
xorl %eax, %eax #
ret
Is there some more tricky situation where it breaks?
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "Jani Nikula" <jani.nikula@intel.com>,
"intel-gfx@lists.freedesktop.org"
<intel-gfx@lists.freedesktop.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"David Gow" <davidgow@google.com>,
"Christian König" <christian.koenig@amd.com>
Subject: Re: [Intel-gfx] [PATCH 0/4] log2: make is_power_of_2() more generic
Date: Thu, 30 Mar 2023 15:18:46 -0700 [thread overview]
Message-ID: <20230330151846.fdbc8edbfbaa6eaddb056dc7@linux-foundation.org> (raw)
In-Reply-To: <549987e4967d45159573901d330c96a0@AcuMS.aculab.com>
On Thu, 30 Mar 2023 21:53:03 +0000 David Laight <David.Laight@ACULAB.COM> wrote:
> > But wouldn't all these issues be addressed by simply doing
> >
> > #define is_power_of_2(n) (n != 0 && ((n & (n - 1)) == 0))
> >
> > ?
> >
> > (With suitable tweaks to avoid evaluating `n' more than once)
>
> I think you need to use the 'horrid tricks' from min() to get
> a constant expression from constant inputs.
This
--- a/include/linux/log2.h~a
+++ a/include/linux/log2.h
@@ -41,11 +41,11 @@ int __ilog2_u64(u64 n)
* *not* considered a power of two.
* Return: true if @n is a power of 2, otherwise false.
*/
-static inline __attribute__((const))
-bool is_power_of_2(unsigned long n)
-{
- return (n != 0 && ((n & (n - 1)) == 0));
-}
+#define is_power_of_2(_n) \
+ ({ \
+ typeof(_n) n = (_n); \
+ n != 0 && ((n & (n - 1)) == 0); \
+ })
/**
* __roundup_pow_of_two() - round up to nearest power of two
_
worked for me in a simple test.
--- a/fs/open.c~b
+++ a/fs/open.c
@@ -1564,3 +1564,10 @@ int stream_open(struct inode *inode, str
}
EXPORT_SYMBOL(stream_open);
+
+#include <linux/log2.h>
+
+int foo(void)
+{
+ return is_power_of_2(43);
+}
_
foo:
# fs/open.c:1573: }
xorl %eax, %eax #
ret
Is there some more tricky situation where it breaks?
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "Jani Nikula" <jani.nikula@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"intel-gfx@lists.freedesktop.org"
<intel-gfx@lists.freedesktop.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"Christian König" <christian.koenig@amd.com>,
"David Gow" <davidgow@google.com>
Subject: Re: [PATCH 0/4] log2: make is_power_of_2() more generic
Date: Thu, 30 Mar 2023 15:18:46 -0700 [thread overview]
Message-ID: <20230330151846.fdbc8edbfbaa6eaddb056dc7@linux-foundation.org> (raw)
In-Reply-To: <549987e4967d45159573901d330c96a0@AcuMS.aculab.com>
On Thu, 30 Mar 2023 21:53:03 +0000 David Laight <David.Laight@ACULAB.COM> wrote:
> > But wouldn't all these issues be addressed by simply doing
> >
> > #define is_power_of_2(n) (n != 0 && ((n & (n - 1)) == 0))
> >
> > ?
> >
> > (With suitable tweaks to avoid evaluating `n' more than once)
>
> I think you need to use the 'horrid tricks' from min() to get
> a constant expression from constant inputs.
This
--- a/include/linux/log2.h~a
+++ a/include/linux/log2.h
@@ -41,11 +41,11 @@ int __ilog2_u64(u64 n)
* *not* considered a power of two.
* Return: true if @n is a power of 2, otherwise false.
*/
-static inline __attribute__((const))
-bool is_power_of_2(unsigned long n)
-{
- return (n != 0 && ((n & (n - 1)) == 0));
-}
+#define is_power_of_2(_n) \
+ ({ \
+ typeof(_n) n = (_n); \
+ n != 0 && ((n & (n - 1)) == 0); \
+ })
/**
* __roundup_pow_of_two() - round up to nearest power of two
_
worked for me in a simple test.
--- a/fs/open.c~b
+++ a/fs/open.c
@@ -1564,3 +1564,10 @@ int stream_open(struct inode *inode, str
}
EXPORT_SYMBOL(stream_open);
+
+#include <linux/log2.h>
+
+int foo(void)
+{
+ return is_power_of_2(43);
+}
_
foo:
# fs/open.c:1573: }
xorl %eax, %eax #
ret
Is there some more tricky situation where it breaks?
next prev parent reply other threads:[~2023-03-30 22:18 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-30 10:42 [PATCH 0/4] log2: make is_power_of_2() more generic Jani Nikula
2023-03-30 10:42 ` [Intel-gfx] " Jani Nikula
2023-03-30 10:42 ` Jani Nikula
2023-03-30 10:42 ` [PATCH 1/4] log2: add helper __IS_POWER_OF_2() Jani Nikula
2023-03-30 10:42 ` [Intel-gfx] " Jani Nikula
2023-03-30 10:42 ` Jani Nikula
2023-03-30 10:42 ` [PATCH 2/4] log2: have is_power_of_2() support bigger types than unsigned long Jani Nikula
2023-03-30 10:42 ` [Intel-gfx] " Jani Nikula
2023-03-30 10:42 ` Jani Nikula
2023-03-30 10:42 ` [PATCH 3/4] log2: allow use of is_power_of_2() in constant expressions Jani Nikula
2023-03-30 10:42 ` [Intel-gfx] " Jani Nikula
2023-03-30 10:42 ` Jani Nikula
2023-03-30 10:42 ` [PATCH 4/4] drm/i915/reg: use is_power_of_2() from log2.h Jani Nikula
2023-03-30 10:42 ` [Intel-gfx] " Jani Nikula
2023-03-30 10:42 ` Jani Nikula
2023-03-30 10:59 ` [PATCH 0/4] log2: make is_power_of_2() more generic Christian König
2023-03-30 10:59 ` [Intel-gfx] " Christian König
2023-03-30 10:59 ` Christian König
2023-03-30 11:10 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for " Patchwork
2023-03-30 11:10 ` [Intel-gfx] ✗ Fi.CI.SPARSE: " Patchwork
2023-03-30 11:23 ` [Intel-gfx] ✓ Fi.CI.BAT: success " Patchwork
2023-03-30 19:50 ` [PATCH 0/4] " Andrew Morton
2023-03-30 19:50 ` [Intel-gfx] " Andrew Morton
2023-03-30 19:50 ` Andrew Morton
2023-03-30 21:53 ` David Laight
2023-03-30 21:53 ` [Intel-gfx] " David Laight
2023-03-30 21:53 ` David Laight
2023-03-30 22:18 ` Andrew Morton [this message]
2023-03-30 22:18 ` Andrew Morton
2023-03-30 22:18 ` [Intel-gfx] " Andrew Morton
2023-03-31 7:33 ` David Laight
2023-03-31 7:33 ` [Intel-gfx] " David Laight
2023-03-31 7:33 ` David Laight
2023-03-31 8:31 ` Jani Nikula
2023-03-31 8:31 ` [Intel-gfx] " Jani Nikula
2023-03-31 8:31 ` Jani Nikula
2023-04-05 15:27 ` Steven Price
2023-04-05 15:27 ` [Intel-gfx] " Steven Price
2023-04-05 15:27 ` Steven Price
2024-04-12 10:01 ` Jani Nikula
2023-03-31 5:58 ` [Intel-gfx] ✓ Fi.CI.IGT: success for " Patchwork
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