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-rw-r--r--arch/x86/include/asm/div64.h22
1 files changed, 14 insertions, 8 deletions
diff --git a/arch/x86/include/asm/div64.h b/arch/x86/include/asm/div64.h
index 9a2d644c08ef..ced283ac79df 100644
--- a/arch/x86/include/asm/div64.h
+++ b/arch/x86/include/asm/div64.h
@@ -4,6 +4,7 @@
#ifdef CONFIG_X86_32
#include <linux/types.h>
+#include <linux/log2.h>
/*
* do_div() is NOT a C function. It wants to return
@@ -21,15 +22,20 @@
({ \
unsigned long __upper, __low, __high, __mod, __base; \
__base = (base); \
- asm("":"=a" (__low), "=d" (__high) : "A" (n)); \
- __upper = __high; \
- if (__high) { \
- __upper = __high % (__base); \
- __high = __high / (__base); \
+ if (__builtin_constant_p(__base) && is_power_of_2(__base)) { \
+ __mod = n & (__base - 1); \
+ n >>= ilog2(__base); \
+ } else { \
+ asm("" : "=a" (__low), "=d" (__high) : "A" (n));\
+ __upper = __high; \
+ if (__high) { \
+ __upper = __high % (__base); \
+ __high = __high / (__base); \
+ } \
+ asm("divl %2" : "=a" (__low), "=d" (__mod) \
+ : "rm" (__base), "0" (__low), "1" (__upper)); \
+ asm("" : "=A" (n) : "a" (__low), "d" (__high)); \
} \
- asm("divl %2":"=a" (__low), "=d" (__mod) \
- : "rm" (__base), "0" (__low), "1" (__upper)); \
- asm("":"=A" (n) : "a" (__low), "d" (__high)); \
__mod; \
})