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Diffstat (limited to 'arch/x86/include/asm/bitops.h')
-rw-r--r--arch/x86/include/asm/bitops.h76
1 files changed, 63 insertions, 13 deletions
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 1775d6e5920e..b97596e2b68c 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -380,6 +380,8 @@ static inline unsigned long __fls(unsigned long word)
return word;
}
+#undef ADDR
+
#ifdef __KERNEL__
/**
* ffs - find first set bit in word
@@ -395,10 +397,25 @@ static inline unsigned long __fls(unsigned long word)
static inline int ffs(int x)
{
int r;
-#ifdef CONFIG_X86_CMOV
+
+#ifdef CONFIG_X86_64
+ /*
+ * AMD64 says BSFL won't clobber the dest reg if x==0; Intel64 says the
+ * dest reg is undefined if x==0, but their CPU architect says its
+ * value is written to set it to the same as before, except that the
+ * top 32 bits will be cleared.
+ *
+ * We cannot do this on 32 bits because at the very least some
+ * 486 CPUs did not behave this way.
+ */
+ long tmp = -1;
+ asm("bsfl %1,%0"
+ : "=r" (r)
+ : "rm" (x), "0" (tmp));
+#elif defined(CONFIG_X86_CMOV)
asm("bsfl %1,%0\n\t"
"cmovzl %2,%0"
- : "=r" (r) : "rm" (x), "r" (-1));
+ : "=&r" (r) : "rm" (x), "r" (-1));
#else
asm("bsfl %1,%0\n\t"
"jnz 1f\n\t"
@@ -422,7 +439,22 @@ static inline int ffs(int x)
static inline int fls(int x)
{
int r;
-#ifdef CONFIG_X86_CMOV
+
+#ifdef CONFIG_X86_64
+ /*
+ * AMD64 says BSRL won't clobber the dest reg if x==0; Intel64 says the
+ * dest reg is undefined if x==0, but their CPU architect says its
+ * value is written to set it to the same as before, except that the
+ * top 32 bits will be cleared.
+ *
+ * We cannot do this on 32 bits because at the very least some
+ * 486 CPUs did not behave this way.
+ */
+ long tmp = -1;
+ asm("bsrl %1,%0"
+ : "=r" (r)
+ : "rm" (x), "0" (tmp));
+#elif defined(CONFIG_X86_CMOV)
asm("bsrl %1,%0\n\t"
"cmovzl %2,%0"
: "=&r" (r) : "rm" (x), "rm" (-1));
@@ -434,11 +466,35 @@ static inline int fls(int x)
#endif
return r + 1;
}
-#endif /* __KERNEL__ */
-
-#undef ADDR
-#ifdef __KERNEL__
+/**
+ * fls64 - find last set bit in a 64-bit word
+ * @x: the word to search
+ *
+ * This is defined in a similar way as the libc and compiler builtin
+ * ffsll, but returns the position of the most significant set bit.
+ *
+ * fls64(value) returns 0 if value is 0 or the position of the last
+ * set bit if value is nonzero. The last (most significant) bit is
+ * at position 64.
+ */
+#ifdef CONFIG_X86_64
+static __always_inline int fls64(__u64 x)
+{
+ long bitpos = -1;
+ /*
+ * AMD64 says BSRQ won't clobber the dest reg if x==0; Intel64 says the
+ * dest reg is undefined if x==0, but their CPU architect says its
+ * value is written to set it to the same as before.
+ */
+ asm("bsrq %1,%0"
+ : "+r" (bitpos)
+ : "rm" (x));
+ return bitpos + 1;
+}
+#else
+#include <asm-generic/bitops/fls64.h>
+#endif
#include <asm-generic/bitops/find.h>
@@ -450,12 +506,6 @@ static inline int fls(int x)
#include <asm-generic/bitops/const_hweight.h>
-#endif /* __KERNEL__ */
-
-#include <asm-generic/bitops/fls64.h>
-
-#ifdef __KERNEL__
-
#include <asm-generic/bitops/le.h>
#include <asm-generic/bitops/ext2-atomic-setbit.h>
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