Divide and C

[Stephen Clamage]

karln!karln at uunet.uu.net (Karl Nicholas) writes:

>    I get a number. I need to use this number to index into a
>    2 dimensional array.

>    EX: int array[10][10];
>        val = 24;
>        ++array[val/10][val%10];

>    This is the only way I know how to do this.
>    My problem with it is that is requires TWO divides.

Some compilers are smart enough to recognize a pattern like
	array[val/10][val%10]
and do a single division, using the resulting quotient and remainder.
Some are smart enough to recognize this pattern across statement
boundaries, e.g.,
	i = a/b; j = a%b;

If your compiler is not this smart and you know that the time spent in
the extra division is making your program unacceptably slow, you can
try the Standard C library function div(), which takes a numerator
and denominator and returns a structure containing the quotient and
remainder.  Use of this function might turn out to be slower than
the extra divide.
-- 

Steve Clamage, TauMetric Corp, steve at taumet.com