You can use all preprocessor features, such as comments and macros, in the assembler. In multi-line macros, you must end each assembly statement with a semicolon ( ; ) because the ( \ ) operator removes newlines. For example:
#define remainder(x,y,z) \ divw z,x,y; \ mullw z,z,y; \ subf z,z,x
asm void newPointlessMath(void)
{
remainder(r3,r4,r5)
blr
}