How to divide two 64-bit numbers in Linux Kernel?

Question

Some code that rounds up the division to demonstrate (C-syntax):

#define SINT64 long long int
#define SINT32 long int

SINT64 divRound(SINT64 dividend, SINT6         


        

Answer 1

Here's my really naive solution. Your mileage may vary.

Keep a sign bit, which is sign(dividend) ^ sign(divisor). (Or *, or /, if you're storing your sign as 1 and -1, as opposed to false and true. Basically, negative if either one is negative, positive if none or both are negative.)

Then, call the unsigned division function on the absolute values of both. Then tack the sign back onto the result.

P.S. That is actually how __divdi3 is implemented in libgcc2.c (from GCC 4.2.3, the version that's installed on my Ubuntu system). I just checked. :-)