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div64.h: optimize do_div() for power-of-two constant divisors

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Let's perform the obvious mask and shift operation in this case.

On 32-bit targets, gcc is able to do the same thing with a constant
divisor that happens to be a power of two i.e. it turns the division
into an inline shift, but it doesn't hurt to be explicit.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
This commit is contained in:
Nicolas Pitre 2015-11-02 14:55:05 -05:00
parent 1c07db4651
commit 911918aa7e
1 changed files with 7 additions and 1 deletions
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8
include/asm-generic/div64.h
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@ -32,6 +32,8 @@
#elif BITS_PER_LONG == 32
#include <linux/log2.h>
extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
/* The unnecessary pointer compare is there
@ -41,7 +43,11 @@ extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
uint32_t __base = (base); \
uint32_t __rem; \
(void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
if (likely(((n) >> 32) == 0)) { \
if (__builtin_constant_p(__base) && \
is_power_of_2(__base)) { \
__rem = (n) & (__base - 1); \
(n) >>= ilog2(__base); \
} else if (likely(((n) >> 32) == 0)) { \
__rem = (uint32_t)(n) % __base; \
(n) = (uint32_t)(n) / __base; \
} else \