aboutsummaryrefslogtreecommitdiff
path: root/include/asm-arm/div64.h
AgeCommit message (Collapse)Author
2007-04-25[NET]: div64_64 consolidate (rev3)Stephen Hemminger
Here is the current version of the 64 bit divide common code. Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2006-12-07[ARM] 3611/4: optimize do_div() when divisor is constantNicolas Pitre
On ARM all divisions have to be performed "manually". For 64-bit divisions that may take more than a hundred cycles in many cases. With 32-bit divisions gcc already use the recyprocal of constant divisors to perform a multiplication, but not with 64-bit divisions. Since the kernel is increasingly relying upon 64-bit divisions it is worth optimizing at least those cases where the divisor is a constant. This is what this patch does using plain C code that gets optimized away at compile time. For example, despite the amount of added C code, do_div(x, 10000) now produces the following assembly code (where x is assigned to r0-r1): adr r4, .L0 ldmia r4, {r4-r5} umull r2, r3, r4, r0 mov r2, #0 umlal r3, r2, r5, r0 umlal r3, r2, r4, r1 mov r3, #0 umlal r2, r3, r5, r1 mov r0, r2, lsr #11 orr r0, r0, r3, lsl #21 mov r1, r3, lsr #11 ... .L0: .word 948328779 .word 879609302 which is the fastest that can be done for any value of x in that case, many times faster than the __do_div64 code (except for the small x value space for which the result ends up being zero or a single bit). The fact that this code is generated inline produces a tiny increase in .text size, but not significant compared to the needed code around each __do_div64 call site this code is replacing. The algorithm used has been validated on a 16-bit scale for all possible values, and then recodified for 64-bit values. Furthermore I've been running it with the final BUG_ON() uncommented for over two months now with no problem. Note that this new code is compiled with gcc versions 4.0 or later. Earlier gcc versions proved themselves too problematic and only the original code is used with them. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2005-04-16Linux-2.6.12-rc2Linus Torvalds
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!