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authorNicolas Pitre <nicolas.pitre@linaro.org>2018-07-25 06:38:54 +0300
committerRussell King <rmk+kernel@armlinux.org.uk>2018-07-30 13:45:53 +0300
commit001a30c4d0e871b21d296e1bcafc6756a1b10607 (patch)
tree513df3ef85de8da961ce9416a8714cbce91c30ce /arch/arm/include/asm/bitops.h
parentcbfc5619e0cc8dcdf3020e27426eec362307cc14 (diff)
downloadlinux-001a30c4d0e871b21d296e1bcafc6756a1b10607.tar.xz
ARM: 8785/1: use compiler built-ins for ffs and fls
On ARMv5 and above, it is beneficial to use compiler built-ins such as __builtin_ffs() and __builtin_ctzl() to implement ffs(), __ffs(), fls() and __fls(). The compiler does inline the clz instruction and even the rbit instruction when available, or provide a constant value when possible. On ARMv4 the compiler calls out to helper functions for those built-ins so it is best to keep the open coded versions in that case. Signed-off-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Diffstat (limited to 'arch/arm/include/asm/bitops.h')
-rw-r--r--arch/arm/include/asm/bitops.h92
1 files changed, 9 insertions, 83 deletions
diff --git a/arch/arm/include/asm/bitops.h b/arch/arm/include/asm/bitops.h
index 4cab9bb823fb..c92e42a5c8f7 100644
--- a/arch/arm/include/asm/bitops.h
+++ b/arch/arm/include/asm/bitops.h
@@ -215,7 +215,6 @@ extern int _find_next_bit_be(const unsigned long *p, int size, int offset);
#if __LINUX_ARM_ARCH__ < 5
-#include <asm-generic/bitops/ffz.h>
#include <asm-generic/bitops/__fls.h>
#include <asm-generic/bitops/__ffs.h>
#include <asm-generic/bitops/fls.h>
@@ -223,93 +222,20 @@ extern int _find_next_bit_be(const unsigned long *p, int size, int offset);
#else
-static inline int constant_fls(int x)
-{
- int r = 32;
-
- if (!x)
- return 0;
- if (!(x & 0xffff0000u)) {
- x <<= 16;
- r -= 16;
- }
- if (!(x & 0xff000000u)) {
- x <<= 8;
- r -= 8;
- }
- if (!(x & 0xf0000000u)) {
- x <<= 4;
- r -= 4;
- }
- if (!(x & 0xc0000000u)) {
- x <<= 2;
- r -= 2;
- }
- if (!(x & 0x80000000u)) {
- x <<= 1;
- r -= 1;
- }
- return r;
-}
-
-/*
- * On ARMv5 and above those functions can be implemented around the
- * clz instruction for much better code efficiency. __clz returns
- * the number of leading zeros, zero input will return 32, and
- * 0x80000000 will return 0.
- */
-static inline unsigned int __clz(unsigned int x)
-{
- unsigned int ret;
-
- asm("clz\t%0, %1" : "=r" (ret) : "r" (x));
-
- return ret;
-}
-
-/*
- * fls() returns zero if the input is zero, otherwise returns the bit
- * position of the last set bit, where the LSB is 1 and MSB is 32.
- */
-static inline int fls(int x)
-{
- if (__builtin_constant_p(x))
- return constant_fls(x);
-
- return 32 - __clz(x);
-}
-
-/*
- * __fls() returns the bit position of the last bit set, where the
- * LSB is 0 and MSB is 31. Zero input is undefined.
- */
-static inline unsigned long __fls(unsigned long x)
-{
- return fls(x) - 1;
-}
-
-/*
- * ffs() returns zero if the input was zero, otherwise returns the bit
- * position of the first set bit, where the LSB is 1 and MSB is 32.
- */
-static inline int ffs(int x)
-{
- return fls(x & -x);
-}
-
/*
- * __ffs() returns the bit position of the first bit set, where the
- * LSB is 0 and MSB is 31. Zero input is undefined.
+ * On ARMv5 and above, the gcc built-ins may rely on the clz instruction
+ * and produce optimal inlined code in all cases. On ARMv7 it is even
+ * better by also using the rbit instruction.
*/
-static inline unsigned long __ffs(unsigned long x)
-{
- return ffs(x) - 1;
-}
-
-#define ffz(x) __ffs( ~(x) )
+#include <asm-generic/bitops/builtin-__fls.h>
+#include <asm-generic/bitops/builtin-__ffs.h>
+#include <asm-generic/bitops/builtin-fls.h>
+#include <asm-generic/bitops/builtin-ffs.h>
#endif
+#include <asm-generic/bitops/ffz.h>
+
#include <asm-generic/bitops/fls64.h>
#include <asm-generic/bitops/sched.h>