From f595ec964daf7f99668039d7303ddedd09a75142 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Thu, 12 Jun 2008 10:47:56 +0200 Subject: common implementation of iterative div/mod We have a few instances of the open-coded iterative div/mod loop, used when we don't expcet the dividend to be much bigger than the divisor. Unfortunately modern gcc's have the tendency to strength "reduce" this into a full mod operation, which isn't necessarily any faster, and even if it were, doesn't exist if gcc implements it in libgcc. The workaround is to put a dummy asm statement in the loop to prevent gcc from performing the transformation. This patch creates a single implementation of this loop, and uses it to replace the open-coded versions I know about. Signed-off-by: Jeremy Fitzhardinge Cc: Andrew Morton Cc: john stultz Cc: Segher Boessenkool Cc: Christian Kujau Cc: Robert Hancock Signed-off-by: Ingo Molnar --- lib/div64.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) (limited to 'lib/div64.c') diff --git a/lib/div64.c b/lib/div64.c index bb5bd0c0f030..76c01542d3e1 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -98,3 +98,26 @@ EXPORT_SYMBOL(div64_u64); #endif #endif /* BITS_PER_LONG == 32 */ + +/* + * Iterative div/mod for use when dividend is not expected to be much + * bigger than divisor. + */ +u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) +{ + u32 ret = 0; + + while (dividend >= divisor) { + /* The following asm() prevents the compiler from + optimising this loop into a modulo operation. */ + asm("" : "+rm"(dividend)); + + dividend -= divisor; + ret++; + } + + *remainder = dividend; + + return ret; +} +EXPORT_SYMBOL(iter_div_u64_rem); -- cgit v1.2.2 From d5e181f78ac753893eb930868a52a4488cd3de0a Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Thu, 12 Jun 2008 10:47:58 +0200 Subject: add an inlined version of iter_div_u64_rem iter_div_u64_rem is used in the x86-64 vdso, which cannot call other kernel code. For this case, provide the always_inlined version, __iter_div_u64_rem. Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Ingo Molnar --- lib/div64.c | 15 +-------------- 1 file changed, 1 insertion(+), 14 deletions(-) (limited to 'lib/div64.c') diff --git a/lib/div64.c b/lib/div64.c index 76c01542d3e1..a111eb8de9cf 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -105,19 +105,6 @@ EXPORT_SYMBOL(div64_u64); */ u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) { - u32 ret = 0; - - while (dividend >= divisor) { - /* The following asm() prevents the compiler from - optimising this loop into a modulo operation. */ - asm("" : "+rm"(dividend)); - - dividend -= divisor; - ret++; - } - - *remainder = dividend; - - return ret; + return __iter_div_u64_rem(dividend, divisor, remainder); } EXPORT_SYMBOL(iter_div_u64_rem); -- cgit v1.2.2