From: Tim Deegan <tim@xen.org>
To: xen-devel@lists.xen.org
Subject: [PATCH v2 4/4] bitmaps/bitops: Clarify tests for small constant size.
Date: Thu, 27 Feb 2014 14:27:13 +0000 [thread overview]
Message-ID: <1393511233-28942-5-git-send-email-tim@xen.org> (raw)
In-Reply-To: <1393511233-28942-1-git-send-email-tim@xen.org>
No semantic changes, just makes the control flow a bit clearer.
I was looking at this bcause the (-!__builtin_constant_p(x) | x__)
formula is too clever for Coverity, but in fact it always takes me a
minute or two to understand it too. :)
Signed-off-by: Tim Deegan <tim@xen.org>
---
v2: fix find_next_bit macros to evaluate 'addr' exactly once.
---
xen/include/asm-x86/bitops.h | 62 ++++++++++++++++++++------------------------
xen/include/xen/bitmap.h | 30 ++++++++++++---------
2 files changed, 46 insertions(+), 46 deletions(-)
diff --git a/xen/include/asm-x86/bitops.h b/xen/include/asm-x86/bitops.h
index ab21d92..05ed2d7 100644
--- a/xen/include/asm-x86/bitops.h
+++ b/xen/include/asm-x86/bitops.h
@@ -335,23 +335,20 @@ static inline unsigned int __scanbit(unsigned long val, unsigned long max)
* @offset: The bitnumber to start searching at
* @size: The maximum size to search
*/
-#define find_next_bit(addr, size, off) ({ \
- unsigned int r__ = (size); \
- unsigned int o__ = (off); \
- switch ( -!__builtin_constant_p(size) | r__ ) \
- { \
- case 0: (void)(addr); break; \
- case 1 ... BITS_PER_LONG: \
- r__ = o__ + __scanbit(*(const unsigned long *)(addr) >> o__, r__); \
- break; \
- default: \
- if ( __builtin_constant_p(off) && !o__ ) \
- r__ = __find_first_bit(addr, r__); \
- else \
- r__ = __find_next_bit(addr, r__, o__); \
- break; \
- } \
- r__; \
+#define find_next_bit(addr, size, off) ({ \
+ unsigned int r__; \
+ const unsigned long *a__ = (addr); \
+ unsigned int s__ = (size); \
+ unsigned int o__ = (off); \
+ if ( __builtin_constant_p(size) && s__ == 0 ) \
+ r__ = s__; \
+ else if ( __builtin_constant_p(size) && s__ <= BITS_PER_LONG ) \
+ r__ = o__ + __scanbit(*(const unsigned long *)(a__) >> o__, s__); \
+ else if ( __builtin_constant_p(off) && !o__ ) \
+ r__ = __find_first_bit(a__, s__); \
+ else \
+ r__ = __find_next_bit(a__, s__, o__); \
+ r__; \
})
/**
@@ -370,23 +367,20 @@ static inline unsigned int __scanbit(unsigned long val, unsigned long max)
* @offset: The bitnumber to start searching at
* @size: The maximum size to search
*/
-#define find_next_zero_bit(addr, size, off) ({ \
- unsigned int r__ = (size); \
- unsigned int o__ = (off); \
- switch ( -!__builtin_constant_p(size) | r__ ) \
- { \
- case 0: (void)(addr); break; \
- case 1 ... BITS_PER_LONG: \
- r__ = o__ + __scanbit(~*(const unsigned long *)(addr) >> o__, r__); \
- break; \
- default: \
- if ( __builtin_constant_p(off) && !o__ ) \
- r__ = __find_first_zero_bit(addr, r__); \
- else \
- r__ = __find_next_zero_bit(addr, r__, o__); \
- break; \
- } \
- r__; \
+#define find_next_zero_bit(addr, size, off) ({ \
+ unsigned int r__; \
+ const unsigned long *a__ = (addr); \
+ unsigned int s__ = (size); \
+ unsigned int o__ = (off); \
+ if ( __builtin_constant_p(size) && s__ == 0 ) \
+ r__ = s__; \
+ else if ( __builtin_constant_p(size) && s__ <= BITS_PER_LONG ) \
+ r__ = o__ + __scanbit(~*(const unsigned long *)(a__) >> o__, s__); \
+ else if ( __builtin_constant_p(off) && !o__ ) \
+ r__ = __find_first_zero_bit(a__, s__); \
+ else \
+ r__ = __find_next_zero_bit(a__, s__, o__); \
+ r__; \
})
/**
diff --git a/xen/include/xen/bitmap.h b/xen/include/xen/bitmap.h
index b5ec455..166e1a0 100644
--- a/xen/include/xen/bitmap.h
+++ b/xen/include/xen/bitmap.h
@@ -110,13 +110,14 @@ extern int bitmap_allocate_region(unsigned long *bitmap, int pos, int order);
#define bitmap_bytes(nbits) (BITS_TO_LONGS(nbits) * sizeof(unsigned long))
-#define bitmap_switch(nbits, zero_ret, small, large) \
- switch (-!__builtin_constant_p(nbits) | (nbits)) { \
- case 0: return zero_ret; \
- case 1 ... BITS_PER_LONG: \
- small; break; \
- default: \
- large; break; \
+#define bitmap_switch(nbits, zero, small, large) \
+ unsigned int n__ = (nbits); \
+ if (__builtin_constant_p(nbits) && n__ == 0) { \
+ zero; \
+ } else if (__builtin_constant_p(nbits) && n__ <= BITS_PER_LONG) { \
+ small; \
+ } else { \
+ large; \
}
static inline void bitmap_zero(unsigned long *dst, int nbits)
@@ -191,7 +192,8 @@ static inline void bitmap_complement(unsigned long *dst, const unsigned long *sr
static inline int bitmap_equal(const unsigned long *src1,
const unsigned long *src2, int nbits)
{
- bitmap_switch(nbits, -1,
+ bitmap_switch(nbits,
+ return -1,
return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)),
return __bitmap_equal(src1, src2, nbits));
}
@@ -199,7 +201,8 @@ static inline int bitmap_equal(const unsigned long *src1,
static inline int bitmap_intersects(const unsigned long *src1,
const unsigned long *src2, int nbits)
{
- bitmap_switch(nbits, -1,
+ bitmap_switch(nbits,
+ return -1,
return ((*src1 & *src2) & BITMAP_LAST_WORD_MASK(nbits)) != 0,
return __bitmap_intersects(src1, src2, nbits));
}
@@ -207,21 +210,24 @@ static inline int bitmap_intersects(const unsigned long *src1,
static inline int bitmap_subset(const unsigned long *src1,
const unsigned long *src2, int nbits)
{
- bitmap_switch(nbits, -1,
+ bitmap_switch(nbits,
+ return -1,
return !((*src1 & ~*src2) & BITMAP_LAST_WORD_MASK(nbits)),
return __bitmap_subset(src1, src2, nbits));
}
static inline int bitmap_empty(const unsigned long *src, int nbits)
{
- bitmap_switch(nbits, -1,
+ bitmap_switch(nbits,
+ return -1,
return !(*src & BITMAP_LAST_WORD_MASK(nbits)),
return __bitmap_empty(src, nbits));
}
static inline int bitmap_full(const unsigned long *src, int nbits)
{
- bitmap_switch(nbits, -1,
+ bitmap_switch(nbits,
+ return -1,
return !(~*src & BITMAP_LAST_WORD_MASK(nbits)),
return __bitmap_full(src, nbits));
}
--
1.8.5.2
next prev parent reply other threads:[~2014-02-27 14:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-27 14:27 [PATCH v2 0/4] more Coverity-inspired tidying Tim Deegan
2014-02-27 14:27 ` [PATCH v2 1/4] common/vsprintf: Explicitly treat negative lengths as 'unlimited' Tim Deegan
2014-02-28 15:07 ` Keir Fraser
2014-02-27 14:27 ` [PATCH v2 2/4] x86/shadow: Drop shadow_mode_trap_reads() Tim Deegan
2014-02-27 14:27 ` [PATCH v2 3/4] x86/mem_sharing: drop unused variable Tim Deegan
2014-02-27 14:27 ` Tim Deegan [this message]
2014-02-27 16:30 ` [PATCH v2 4/4] bitmaps/bitops: Clarify tests for small constant size Jan Beulich
2014-02-27 16:38 ` Tim Deegan
2014-02-28 14:40 ` Jan Beulich
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