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/*
 * disasm.c -- disassembler
 */
 
 
#include "common.h"
#include "stdarg.h"
#include "romlib.h"
#include "instr.h"
#include "disasm.h"
 
 
static char instrBuffer[100];
 
 
static void disasmN(char *opName, Word immed) {
  if (immed == 0) {
    sprintf(instrBuffer, "%-7s", opName);
  } else {
    sprintf(instrBuffer, "%-7s %08X", opName, immed);
  }
}
 
 
static void disasmRH(char *opName, int r1, Half immed) {
  sprintf(instrBuffer, "%-7s $%d,%04X", opName, r1, immed);
}
 
 
static void disasmRHH(char *opName, int r1, Half immed) {
  sprintf(instrBuffer, "%-7s $%d,%08X", opName, r1, (Word) immed << 16);
}
 
 
static void disasmRRH(char *opName, int r1, int r2, Half immed) {
  sprintf(instrBuffer, "%-7s $%d,$%d,%04X", opName, r1, r2, immed);
}
 
 
static void disasmRRS(char *opName, int r1, int r2, Half immed) {
  sprintf(instrBuffer, "%-7s $%d,$%d,%s%04X", opName, r1, r2,
          SIGN(16) & immed ? "-" : "+",
          SIGN(16) & immed ? -(signed)SEXT16(immed) : SEXT16(immed));
}
 
 
static void disasmRRR(char *opName, int r1, int r2, int r3) {
  sprintf(instrBuffer, "%-7s $%d,$%d,$%d", opName, r1, r2, r3);
}
 
 
static void disasmRRB(char *opName, int r1, int r2, Half offset, Word locus) {
  sprintf(instrBuffer, "%-7s $%d,$%d,%08X", opName,
          r1, r2, (locus + 4) + (SEXT16(offset) << 2));
}
 
 
static void disasmJ(char *opName, Word offset, Word locus) {
  sprintf(instrBuffer, "%-7s %08X", opName,
          (locus + 4) + (SEXT26(offset) << 2));
}
 
 
static void disasmJR(char *opName, int r1) {
  sprintf(instrBuffer, "%-7s $%d", opName, r1);
}
 
 
char *disasm(Word instr, Word locus) {
  Byte opcode;
  Instr *ip;
 
  opcode = (instr >> 26) & 0x3F;
  ip = instrCodeTbl[opcode];
  if (ip == NULL) {
    disasmN("???", 0);
  } else {
    switch (ip->format) {
      case FORMAT_N:
        disasmN(ip->name, instr & 0x03FFFFFF);
        break;
      case FORMAT_RH:
        disasmRH(ip->name, (instr >> 16) & 0x1F, instr & 0x0000FFFF);
        break;
      case FORMAT_RHH:
        disasmRHH(ip->name, (instr >> 16) & 0x1F, instr & 0x0000FFFF);
        break;
      case FORMAT_RRH:
        disasmRRH(ip->name, (instr >> 16) & 0x1F,
                  (instr >> 21) & 0x1F, instr & 0x0000FFFF);
        break;
      case FORMAT_RRS:
        disasmRRS(ip->name, (instr >> 16) & 0x1F,
                  (instr >> 21) & 0x1F, instr & 0x0000FFFF);
        break;
      case FORMAT_RRR:
        disasmRRR(ip->name, (instr >> 11) & 0x1F,
                  (instr >> 21) & 0x1F, (instr >> 16) & 0x1F);
        break;
      case FORMAT_RRX:
        if ((opcode & 1) == 0) {
          /* the FORMAT_RRR variant */
          disasmRRR(ip->name, (instr >> 11) & 0x1F,
                    (instr >> 21) & 0x1F, (instr >> 16) & 0x1F);
        } else {
          /* the FORMAT_RRH variant */
          disasmRRH(ip->name, (instr >> 16) & 0x1F,
                    (instr >> 21) & 0x1F, instr & 0x0000FFFF);
        }
        break;
      case FORMAT_RRY:
        if ((opcode & 1) == 0) {
          /* the FORMAT_RRR variant */
          disasmRRR(ip->name, (instr >> 11) & 0x1F,
                    (instr >> 21) & 0x1F, (instr >> 16) & 0x1F);
        } else {
          /* the FORMAT_RRS variant */
          disasmRRS(ip->name, (instr >> 16) & 0x1F,
                    (instr >> 21) & 0x1F, instr & 0x0000FFFF);
        }
        break;
      case FORMAT_RRB:
        disasmRRB(ip->name, (instr >> 21) & 0x1F,
                  (instr >> 16) & 0x1F, instr & 0x0000FFFF, locus);
        break;
      case FORMAT_J:
        disasmJ(ip->name, instr & 0x03FFFFFF, locus);
        break;
      case FORMAT_JR:
        disasmJR(ip->name, (instr >> 21) & 0x1F);
        break;
      default:
        printf("illegal entry in instruction table\n");
        break;
    }
  }
  return instrBuffer;
}