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| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2015-11-02 14:55:05 -0500 |
|---|---|---|
| committer | Nicolas Pitre <nicolas.pitre@linaro.org> | 2015-11-16 14:14:03 -0500 |
| commit | 911918aa7ef6f868c135505b0015e42072c54682 (patch) | |
| tree | b12a768b34d0461978276533b73436c4494fe71f | |
| parent | 1c07db46511f0d2335d3b32008f644164071d13e (diff) | |
| download | linux-911918aa7ef6f868c135505b0015e42072c54682.tar.gz linux-911918aa7ef6f868c135505b0015e42072c54682.tar.bz2 linux-911918aa7ef6f868c135505b0015e42072c54682.zip | |
div64.h: optimize do_div() for power-of-two constant divisors
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>
| -rw-r--r-- | include/asm-generic/div64.h | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h index 8f4e3193342e..5d974683193a 100644 --- a/include/asm-generic/div64.h +++ b/include/asm-generic/div64.h @@ -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 \ |