Explain how the FFREE instruction works

Question

http://en.wikipedia.org/wiki/X86_instruction_listings

how does the ffree instruction excatly works ? FFREE Free register when i have in FPU STack:

  st2 5 , st1 2, st0 7

then after these instruction(ffree) i have..

   st 1 5, st0 2

is that right?

Answer 1

No, it clears the register without modifying the stack pointer. Whatever register you gave as an argument will be set as empty, but the others will be unchanged.

http://www.website.masmforum.com/tutorials/fptute/fpuchap3.htm#ffree