Implementation of MIPS instructions with subleq
All files are licensed by GPLv3 or later.
Each registers is mapped to the memory.
| Address | Meaning |
|---|---|
| R0–R15 (e.g. 0x100–0x10f) | General registers |
| PC | |
| Lo, Hi (e.g. 0x120, 0x121) | for multiplication |
| Trap | interruption |
There are a few aliases.
| Address | Comment |
|---|---|
| Rd, Imm (0) | |
| Rs (1) | |
| Rt (2) | |
| Mem (3) | the location whither the indirect reference points |
For internal use. It also allows to modify, but they should be restored at the end of the subroutine.
| Address | Comment |
|---|---|
| Inc (4) | stores (-1) |
| Dec (5) | stores (+1) |
| Z (6) | stores 0 |
| T0–T6 (8–e) | temporary registers, stores 0 |
| Word (f) | stores word size (=32) |
Following jump addresses have special meanings.
| Address | Comment |
|---|---|
| End (-1) | implementation is end |
We'll use new instruction in addition to usual subleq.
The type of intsruction is denoted "![a-z]+".
The default when the instruction is ommitted is !subleq.
Name of subroutine that implements a MIPS instruction is "@[a-z]+".
Name of macro is "@@[a-z]+".
Arguments of a macro are "A[:alnum:]*".
Macro expansion is like "$(name Arg0,Arg1,Arg2)".
Format is as shown.
The scope of internal labels "L[:alnum:]*" is limited in a routine or a macro where the label lexically exists.
Comment is as same as that defined in C11.
@add Rd,Rs,Rt
Rs Z; // Z <- -Rs, it assumes Z = 0
Rt Z; // Z <- Z - Rt = -(Rs + Rt)
Rd; // clear Rd
Z Rd;
Z Z End;
becomes (and I assume @add is placed 0x1000)
1 6 3
2 6 6
0 0 9
6 0 c
6 6 (-1)
@mult Rs,Rt // incomplete
Z Rs Lns; // if Rs < 0 then Lns else Lps
Lps:Rs Z; Z T2; Z Z Lmultu; // T2 <- Rs = abs(Rs)
Lns:Rs T2; Dec T1; // T2 <- -Rs = abs(Rs), T1 <- -1
Lmultu:Lo; // it's ok because Rt and lo are not aliased.
$(@@multu Lo,T2,Rt,Linv); // lo <- abs(Rs) * (-Rt)
Linv:Z T1 Lend; // if Rs < 0 (i.e. T1 < 0) then Lend else next
Lo T1; T1 Z; Lo; Z lo Lend; // (in this case Rs >= 0 and T1 = 0), lo <- -lo
Lend:T1; T2; Z Z End;
@@multu Ad,Ax,Ay,Aend // internal subroutine macro: Ad <- Ax * (-Ay) + Ad; assumes Ax >= 0; modifies Ax, Ad
Lloop:Dec Ax Aend;
Ay Ad Lloop;
is equivalent to
@mult Rs,Rt // imcomplete sample: lo <- Rs * Rt
Z Rs Lns; // if Rs < 0 then Lns else Lps
Lps:Rs Z; Z T2; Z Z Lmultu; // T2 <- Rs = abs(Rs)
Lns:Rs T2; Dec T1; // T2 <- -Rs = abs(Rs), T1 <- -1
Lmultu:Lo; // it's ok because Rt and lo are not aliased.
// $(@@multu Lo,T2,Rt,Linv); // lo <- abs(Rs) * (-Rt)
Lmultuloop:Dec T2 Linv;
Rt Lo Lmultuloop;
Linv:Z T1 Lend; // if Rs < 0 (i.e. T1 < 0) then Lend else next
Lo T1; T1 Z; Lo; Z Lo Lend; // (in this case Rs >= 0 and T1 = 0), lo <- -lo
Lend:T1; T2; Z Z End;
and (and I assume @mult is placed 0x2000)
2000: 6 1 2006 // Z Rs Lns;
2003: 1 6 2006 // Lps:Rs Z;
2006: 6 10 2009 // Z T2;
2009: 6 6 2012// Z Z Lmultu
200c: 1 10 200f // Lns:Rs T2;
200f: 5 9 2012 // dec T1;
2012: 120 120 2015 // Lmultu:lo;
2015: 5 10 201b // Lmultuloop:dec T2 Linv;
2018: 3 120 2015 // Rt lo Lmultuloop;
201b: 6 9 202a // Linv:Z T1 Lend;
201e: 120 9 2021 // lo T1;
2021: 9 6 2024 // T1 Z;
2024: 120 120 2027 // lo;
2027: 6 120 202a // Z lo Lend;
202a: 9 9 202d // Lend:T1;
202d: 10 10 2030 // T2;
2030: 6 6 (-1) // Z Z End;