.so init
.SH
B. IMPLEMENTATION
.SH
B.1. Excerpts from the non-optimized EM_table
.PP
Even though the non-optimized version of the EM_table is relatively
straight-forward, examples have never hurt anybody.
One of the simplest instructions is the \*(Siloc\*(So, which appears in
our EM_table as follows:
.DS
\f6
.TA 8 16 24 32 40 48 56 64
C_loc	==>	"set	$1, T1";
		"dec	4, SP";
		"st	T1, [SP]".
\f1
.DE
Just as \*(SiSP\*(So is an alias for \*(Si%l0\*(So, \*(SiT1\*(So is
an alias for \*(Si%g1\*(So.
A little more complex is the \*(Siadi\*(So which performs integer
addition.
.DS
\f6
C_adi	==>	"ld	[SP], T1";
		"ld	[SP+4], T2";
		"add	T1, T2, T3";
		"st	T3, [SP+4];
		"inc	4, SP".
\f1
.DE
We could go on with even more complex instructions, but since that would
not contribute to anything the reader is referred to the implementation
for more details.
.SH
B.2. Excerpts from the optimized EM_table
.PP
The optimized EM_table uses the cache primitives mentioned in chapter 4.
This means that the \*(Siloc\*(So this time appears as
.DS
\f6
C_loc	==>	push_const($1).
\f1
.DE
The \*(Silol\*(So can now be written as
.DS
\f6
C_lol	==>	push_reg(LB);
		inc_tos($1);
		push_const(4);
		C_los(4).
\f1
.DE
Due to the law of conservation of misery somebody has to do the dirty work.
In this case, it is the \*(Silos\*(So. To show just a small part of
the implementation of the \*(Silos\*(So:
.DS
\f6
C_los	$1 == 4	==>
		if (type_of_tos() == T_cst) {
			arith size;
			const_str_t n;

			size= pop_const();
			if (size <= 4) {
				reg_t a;
				reg_t a;
				char *LD;

				switch (size) {
				case 1:	LD = "ldub"; break;
				case 2:	LD = "lduh"; break;
				case 4:	LD = "ld"; break;
				default:	arg_error("C_los", size);
				}
				a = pop_reg_c13(n);
				b = alloc_reg();
				"$LD	[$a+$n], $b";
				push_reg(b);
				free_reg(a);
			} else ...
\f1
.DE
For the full implementation, the reader is again referred to the actual
implementation. Just to show how other instructions are affected
by the optimization we will show that implementation of the \*(Sitge\*(So
instruction:
.DS
\f6
C_tge	==>	{
			reg_t a;
			reg_t b;

			a = pop_reg();
			b = alloc_reg();
			"	tst	$a";
			"	bge,a	1f";
			"	mov	1, $b";		/* delay slot */
			"	set	0, $b";
			"1:";
			free_reg(a);
			push_reg(b);
		}.

\f1
.DE
.SH
.bp
CREDITS
.PP
In order of appearance:
.TS
center;
r c l.
Original idea	-	Dick Grune
Design & implementation	-	Philip Homburg
	-	Raymond Michiels
Tutor	-	Dick Grune
Assistant Tutor	-	Ceriel Jacobs
Proofreading	-	Dick Grune
	-	Hans van Eck
.TE
.SH
REFERENCES
.PP
.[
$LIST$
.]
