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#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <arpa/inet.h>
#define MEM_SIZE 36
#define RA 31
#define V0 2
#define V1 3
#define A0 4
#define A1 5
#define A2 6
#define A3 7
#define WORD_SIZE 4
typedef struct {
unsigned int op: 6;
unsigned int rs: 5;
unsigned int rt: 5;
unsigned int rd: 5;
unsigned int shamt: 5;
unsigned int func: 6;
} rtype_t;
typedef struct {
unsigned int op: 6;
unsigned int rs: 5;
unsigned int rt: 5;
unsigned int imm: 16;
} itype_t;
typedef struct {
unsigned int op: 6;
unsigned int addr: 26;
} jtype_t;
typedef enum { NOP, RTYPE, ITYPE, JTYPE } type_t;
typedef struct {
type_t type;
union {
uint32_t value;
rtype_t r;
jtype_t j;
itype_t i;
};
} inst_t;
uint8_t memory[MEM_SIZE] = {0};
uint32_t pc = 0, hi = 0, lo = 0;
uint32_t regFile[32] = {0};
/* InstFetch: Fetch the next instruction from memory into the given
* instruction */
void InstFetch(inst_t *inst) {
uint32_t value = 0;
memcpy(&value, memory + pc, WORD_SIZE);
switch ((value & 0xFC000000) >> 24) {
case 0:
inst->type = RTYPE;
inst->r.op = (value & 0xFC000000) >> 26;
inst->r.rs = (value & 0x03E00000) >> 21;
inst->r.rt = (value & 0x001F0000) >> 16;
inst->r.rd = (value & 0x0000F800) >> 11;
inst->r.shamt = (value & 0x000007C0) >> 6;
inst->r.func = value & 0x0000002F;
break;
case 2:
case 3:
inst->type = JTYPE;
inst->j.op = (value & 0xFC000000) >> 26;
inst->j.addr = value & 0X03FFFFFF;
break;
default:
inst->type = ITYPE;
inst->i.op = (value & 0xFC000000) >> 26;
inst->i.rs = (value & 0x03E00000) >> 21;
inst->i.rt = (value & 0x001F0000) >> 16;
inst->i.imm = value & 0x0000FFFF;
break;
}
if (inst->value == 0) {
inst->type = NOP;
}
pc += WORD_SIZE;
}
void Syscall(void) {
char c, *s;
switch (regFile[V0]) {
case 1: // print integer
printf("%d", regFile[A0]);
break;
case 2: // print float
break;
case 3: // print double
break;
case 4: // print string
printf("%s", memory + regFile[A0]);
break;
case 5: // read integer
scanf("%d", (int *)regFile + V0);
break;
case 6: // read float
break;
case 7: // read double
break;
case 8: // read string
s = (char *)calloc(regFile[A0], sizeof(char));
fgets(s, regFile[A0], stdin);
memcpy(memory + regFile[A1], s, regFile[A0]);
free(s);
break;
case 9: // sbrk
break;
case 10: //exit
exit(0);
case 11: // print char
printf("%c", regFile[A0]);
break;
case 12: // read char
c = 0;
scanf("%c", &c);
regFile[V0] = c;
break;
case 13: // open file
break;
case 14: // read from file
break;
case 15: // write to file
break;
case 16: // close file
break;
case 17: // exit2
exit(regFile[A0]);
}
}
/* ExecRtype: Execute a given R-Type instruction */
void ExecRtype(const inst_t inst) {
rtype_t r = inst.r;
uint32_t a = regFile[r.rs], b = regFile[r.rt];
uint64_t mult = 0;
switch (r.func) {
case 32: // add
regFile[r.rd] = (signed)a + (signed)b;
break;
case 33: // addu
regFile[r.rd] = a + b;
break;
case 36: // and
regFile[r.rd] = a & b;
break;
case 37: // or
regFile[r.rd] = a | b;
break;
case 42: // slt
regFile[r.rd] = (signed)a < (signed)b;
break;
case 43: // sltu
regFile[r.rd] = a < b;
break;
case 34: // sub
regFile[r.rd] = (signed)a - (signed)b;
break;
case 35: // subu
regFile[r.rd] = a - b;
break;
case 38: // xor
regFile[r.rd] = a ^ b;
break;
case 0: // sll
regFile[r.rd] = b << r.shamt;
break;
case 3: // sra
regFile[r.rd] = (signed)b >> r.shamt;
break;
case 2: // srl
regFile[r.rd] = b >> r.shamt;
break;
case 26: // div
hi = (signed)a % (signed)b;
lo = (signed)a / (signed)b;
break;
case 27: // divu
hi = a % b;
lo = a / b;
break;
case 24: // mult
mult = (signed)a * (signed)b;
hi = (0xFFFFFFFF00000000 & mult) >> 32;
lo = 0x00000000FFFFFFFF & mult;
break;
case 25: // multu
mult = a * b;
hi = (0xFFFFFFFF00000000 & mult) >> 32;
lo = 0x00000000FFFFFFFF & mult;
break;
case 16: // MFHI
regFile[r.rd] = hi;
break;
case 18: // MFLO
regFile[r.rd] = lo;
break;
case 17: // MTHI
hi = regFile[r.rs];
break;
case 19: // MTLO
lo = regFile[r.rs];
break;
case 8: // jr
pc = a;
break;
case 9: // jalr
regFile[r.rd] = pc + 4;
pc = a;
break;
case 12: // syscall
Syscall();
break;
}
}
/* InstExec: Execute a given instruction */
void InstExec(const inst_t inst) {
if (inst.type == NOP) {
return;
}
switch (inst.j.op) {
case 0: // R-type instruction
ExecRtype(inst);
break;
case 3: // jal
regFile[RA] = pc + 4;
/* intentional fall through */
case 2: // j
pc = (0xF0000000 & pc ) | inst.j.addr;
break;
case 4: // beq
pc = (regFile[inst.i.rs] == regFile[inst.i.rt]) ? pc + 4 +
inst.i.imm : pc;
break;
case 5: // bne
pc = (regFile[inst.i.rs] != regFile[inst.i.rt]) ? pc + 4 +
inst.i.imm : pc;
break;
case 8: // addi
regFile[inst.i.rt] = (signed)inst.i.rs + (signed)inst.i.imm;
break;
case 9: // addiu
regFile[inst.i.rt] = inst.i.rs + inst.i.imm;
break;
case 12: // andi
regFile[inst.i.rt] = inst.i.rs & inst.i.imm;
break;
case 13: // ori
regFile[inst.i.rt] = inst.i.rs | inst.i.imm;
break;
case 14: // xori
regFile[inst.i.rt] = inst.i.rs ^ inst.i.imm;
break;
case 10: // slti
regFile[inst.i.rt] = (signed)inst.i.rs < (signed)inst.i.imm;
break;
case 11: // sltiu
regFile[inst.i.rt] = inst.i.rs < inst.i.imm;
break;
case 15: // lui
regFile[inst.i.rt] = inst.i.imm << 16;
break;
case 35: // lw
memcpy(regFile + inst.i.rs, memory + inst.i.rt + inst.i.imm,
WORD_SIZE);
break;
case 43: // sw
memcpy(memory + inst.i.rt + inst.i.imm, regFile + inst.i.rs,
WORD_SIZE);
break;
}
}
void CycleCpu(void) {
inst_t instFetch, instExec;
memset(&instFetch, 0, sizeof(inst_t));
memset(&instExec, 0, sizeof(inst_t));
while (pc < MEM_SIZE) {
InstFetch(&instFetch);
InstExec(instExec);
instExec = instFetch;
}
}
int LoadBinary(const char * const path) {
FILE *fp = fopen(path, "r");
if (fp == NULL) {
perror("LoadBinary");
return -1;
}
int8_t byte = 0;
size_t i = 0;
while ((byte = fgetc(fp)) != EOF && i < MEM_SIZE) {
memory[i++] = byte;
}
fclose(fp);
return 0;
}
int main(int argc, char *argv[]) {
if (LoadBinary(*++argv) == -1) {
return -1;
}
CycleCpu();
}
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