1993-03-31 13:22:17 +00:00
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.In
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1991-09-27 16:19:24 +00:00
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.SH
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B. IMPLEMENTATION
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.SH
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B.1. Excerpts from the non-optimized EM_table
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.PP
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Even though the non-optimized version of the EM_table is relatively
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straight-forward, examples have never hurt anybody.
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One of the simplest instructions is the \*(Siloc\*(So, which appears in
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our EM_table as follows:
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.DS
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\f6
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.TA 8 16 24 32 40 48 56 64
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C_loc ==> "set $1, T1";
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"dec 4, SP";
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"st T1, [SP]".
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\f1
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.DE
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Just as \*(SiSP\*(So is an alias for \*(Si%l0\*(So, \*(SiT1\*(So is
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an alias for \*(Si%g1\*(So.
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A little more complex is the \*(Siadi\*(So which performs integer
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addition.
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.DS
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\f6
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C_adi ==> "ld [SP], T1";
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"ld [SP+4], T2";
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"add T1, T2, T3";
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"st T3, [SP+4];
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"inc 4, SP".
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\f1
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.DE
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We could go on with even more complex instructions, but since that would
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not contribute to anything the reader is referred to the implementation
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for more details.
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.SH
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B.2. Excerpts from the optimized EM_table
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.PP
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The optimized EM_table uses the cache primitives mentioned in chapter 4.
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This means that the \*(Siloc\*(So this time appears as
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.DS
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\f6
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C_loc ==> push_const($1).
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\f1
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.DE
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The \*(Silol\*(So can now be written as
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.DS
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\f6
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C_lol ==> push_reg(LB);
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inc_tos($1);
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push_const(4);
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C_los(4).
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\f1
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.DE
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Due to the law of conservation of misery somebody has to do the dirty work.
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In this case, it is the \*(Silos\*(So. To show just a small part of
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the implementation of the \*(Silos\*(So:
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.DS
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\f6
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C_los $1 == 4 ==>
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if (type_of_tos() == T_cst) {
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arith size;
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const_str_t n;
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size= pop_const();
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if (size <= 4) {
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reg_t a;
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reg_t a;
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char *LD;
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switch (size) {
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case 1: LD = "ldub"; break;
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case 2: LD = "lduh"; break;
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case 4: LD = "ld"; break;
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default: arg_error("C_los", size);
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}
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a = pop_reg_c13(n);
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b = alloc_reg();
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"$LD [$a+$n], $b";
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push_reg(b);
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free_reg(a);
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} else ...
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\f1
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.DE
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For the full implementation, the reader is again referred to the actual
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implementation. Just to show how other instructions are affected
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by the optimization we will show that implementation of the \*(Sitge\*(So
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instruction:
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.DS
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\f6
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C_tge ==> {
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reg_t a;
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reg_t b;
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a = pop_reg();
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b = alloc_reg();
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" tst $a";
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" bge,a 1f";
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" mov 1, $b"; /* delay slot */
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" set 0, $b";
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"1:";
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free_reg(a);
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push_reg(b);
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}.
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\f1
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.DE
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.SH
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.bp
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CREDITS
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.PP
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In order of appearance:
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.TS
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center;
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r c l.
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Original idea - Dick Grune
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Design & implementation - Philip Homburg
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- Raymond Michiels
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Tutor - Dick Grune
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Assistant Tutor - Ceriel Jacobs
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Proofreading - Dick Grune
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- Hans van Eck
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.TE
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.SH
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REFERENCES
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.PP
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.[
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$LIST$
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.]
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