From: Nicolas Pitre Date: Mon, 2 Nov 2015 19:55:05 +0000 (-0500) Subject: div64.h: optimize do_div() for power-of-two constant divisors X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=911918aa7ef6f868c135505b0015e42072c54682;p=deliverable%2Flinux.git 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 --- 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 + 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 \