div64.h: optimize do_div() for power-of-two constant divisors (911918aa) · Commits · 戴 / test

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>

include/asm-generic/div64.h

+7 −1

Original line number	Diff line number	Diff line
		@@ -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 \

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