On Thu, Nov 06, 2014 at 04:23:18PM +0000, Mans Rullgard wrote: > This is an adaptation of the optimised do_div() for ARM by > Nicolas Pitre implementing division by a constant using a > multiplication by the inverse. Ideally, the compiler would > do this internally as it does for 32-bit operands, but it > doesn't. > > This version of the code requires an assembler with support > for the DSP ASE syntax since accessing the hi/lo registers > sanely from inline asm is impossible without this. Building > for a CPU without this extension still works, however. > > It also does not protect against the WAR hazards for the > hi/lo registers present on CPUs prior to MIPS IV. > > I have only tested it as far as booting and light use with > the BUG_ON enabled wihtout encountering any issues. > > The inverse computation code is a straight copy from ARM, > so this should probably be moved to a shared location. Can you explain why you need __div64_fls()? There's __fls() which on MIPS is carefully written to make use of the CLZ rsp. DCLZ instructions where available; the fallback implementation is looking fairly similar to your code. MADD is named MAD on some older CPUs; yet other CPUs don't have it at all. I take it you tried to make GCC emit the instruction but it doesn't? Ralf
