Section 3 with Remik (rz33@cornell.edu) 
Meeting #8 Notes
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Administrivia:	Assignment #3 is out
Review:		Frame Base Registers by Example (Bali->SAM)



Bali program:
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main()
  int x, y;
  x := 3;
  y := 4;
  return euclideanDistanceSquared(x, y);

euclideanDistanceSquared(x, y)
  x := sqr(x);
  y := sqr(y);

  return (x + y);

sqr(x)
  return (x * x);

SAM equivalent:
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virtual_machine:
// reserve return variable
PUSHIMM 0
// save where main entry was
PUSHFBR
// load the new offset for the next frame
PUSHIMM 1
POPFBR
// load the program
JSR main
POPFBR
STOP
===========================================================
main:
// we have 2 local variables, the return will use the frame
ADDSP 2
PUSHIMM 3
STOREOFF 1
PUSHIMM 4
STOREOFF 2
// prepare for function call
// first allocate the return variable placeholder
PUSHIMM 0
// remember the state for 'main'
PUSHFBR
// set up the parameters to be passed
PUSHOFF 1
PUSHOFF 2
PUSHSP
// # of arguments plus 1
PUSHIMM 3
SUB
POPFBR
// now call function to get Euclidean Distance Squared
JSR euclideanDistanceSquared
// clean up by removing passed arguments
ADDSP -2
POPFBR
// now return
// first copy the value returned from function call to virtual_machine frame
STOREOFF -1
// remove local variables - x & y
ADDSP -2
// go to caller - virtual_machine
JUMPIND
===========================================================
euclideanDistanceSquared:
// no local variables, just function calls
// prepare for function call on variable x
PUSHIMM 0
PUSHFBR
// supply x as function argument
PUSHOFF 1
PUSHSP
PUSHIMM 2
SUB
POPFBR
JSR sqr
ADDSP -1
POPFBR
// assign result to x, which is only a temporary cell
STOREOFF 1

// prepare to call function with y
PUSHIMM
PUSHFBR
// supply y as argument
PUSHOFF 1
PUSHSP
PUSHIMM 2
SUB
POPFBR
JSR sqr
ADDSP -1
POPFBR
// assign result to y
STOREOFF

// add x & y and return
PUSHOFF 1
PUSHOFF 2
ADD
// make the result the return variable
STOREOFF -1
JUMPIND
===========================================================
sqr:
// no local variables, just 1 expression to be returned
// x * x
PUSHOFF 1
PUSHOFF 1
TIMES
// return (x*x)
STOREOFF -1
JUMPIND