MIPS alu question

[Deeko]

Ok, apparently, for the SLT MIPS instruction, the output is basically based on the adder result from the most signifigant bit.

This doesn't make sense to me. Seems it will only tell you if a is not positive and b is(since its two's compliment). Am I missing something?

http://www.cs.drexel.edu/~anatole/teach...05_cs281/assignments/Figure_B.5.12.jpg