jb302@28: /* mem.c
jb302@28:  * functions for accessing emulator memory */
jb302@28: #include "mem.h"
jb302@28: 
jb302@28: /* get flag value
jb302@28:  * if invalid flag is requested value is 0 */
jb302@28: BYTE
jb302@28: get_flag(BYTE flag) {
jb302@28:     if (flag > 7) {
jb302@28:         return 0;
jb302@28:     }
jb302@28:     else {
jb302@28:         return GBIT(flags, flag);
jb302@28:     }
jb302@28: }
jb302@28: 
jb302@28: /*  set flag to 0 if on == 0
jb302@28:  *  otherwise set flag to 1 */
jb302@28: void
jb302@28: set_flag(BYTE flag, BYTE on) {
jb302@28:     if (flag <= 7) {
jb302@29:         if (on == 0x00) {
jb302@29:             flags = CBIT(flags, flag);
jb302@29:         }
jb302@29:         else {
jb302@29:             flags = SBIT(flags, flag);
jb302@28:         }
jb302@28:     }
jb302@28: }
jb302@28: 
jb302@30: /* sets zero and parity flags based on content of byte */
jb302@30: void
jb302@30: set_zp(BYTE val){
jb302@30:     if (val == 0) {
jb302@30:         set_flag(Z, 1);
jb302@30:         set_flag(P, 0);
jb302@30:     }
jb302@30:     else {
jb302@34:         /* check parity
jb302@34:          * think of this as folding */
jb302@30:         val ^= val >> 4;
jb302@30:         val ^= val >> 2;
jb302@30:         val ^= val >> 1;
jb302@30:         val &= 1;
jb302@30:         if (val == 0) {
jb302@30:             set_flag(P, 1);
jb302@30:         }
jb302@30:         else {
jb302@30:             set_flag(P, 0);
jb302@30:         }
jb302@30:     }
jb302@30: }
jb302@30: 
jb302@28: WIDE
jb302@28: get_wide(BYTE reg) {
jb302@29:     /* high, low */
jb302@29:     return MWIDE(regs[reg + 4], regs[reg + 12]);
jb302@28: }
jb302@28: 
jb302@28: void
jb302@28: set_wide(BYTE reg, WIDE val) {
jb302@29:     regs[reg + 4] = GHIGH(val); /* high */
jb302@29:     regs[reg + 12] = GLOW(val); /* low */
jb302@28: }
jb302@28: 
jb302@28: void 
jb302@28: inc_pc(BYTE n) {
jb302@28:     if ((regs[PCL] + n) > 0xFF) {
jb302@28:         regs[PCH]++;
jb302@28:     }
jb302@28:     regs[PCL] += n;
jb302@28: }
jb302@28: 
jb302@28: BYTE 
jb302@28: fetch(void) {
jb302@28:     BYTE val = mem[get_wide(PC)];
jb302@28:     inc_pc(1);
jb302@28:     return val;
jb302@28: }
jb302@28: 
jb302@28: WIDE
jb302@28: fetch_wide(void) {
jb302@30:     WIDE val = MWIDE(mem[get_wide(PC)], mem[get_wide(PC) + 1]);
jb302@28:     inc_pc(2);
jb302@28:     return val;
jb302@28: }
jb302@28: 
jb302@29: /* 0b000 = R0
jb302@29:  * 0b001 = R1
jb302@29:  * 0b010 = R2
jb302@29:  * 0b011 = R3
jb302@29:  * 0b100 = DPH
jb302@29:  * 0b101 = DPL
jb302@29:  * 0b110 = SPH
jb302@29:  * 0b111 = SPL */
jb302@29: BYTE 
jb302@29: get_reg(BYTE reg) {
jb302@29:     if (reg < 4) {
jb302@29:         return regs[reg | (get_flag(BS) << 3)];
jb302@29:     }
jb302@29:     else {
jb302@29:         switch (reg) {
jb302@29:             
jb302@29:             case 4:
jb302@29:                 return regs[DPH];
jb302@29:             case 5:
jb302@29:                 return regs[DPL];
jb302@29:             case 6:
jb302@29:                 return regs[SPH];
jb302@29:             case 7:
jb302@29:                 return regs[SPL];
jb302@29:             default:
jb302@29:                 return 0;
jb302@29:         }
jb302@29:     }
jb302@29: }
jb302@28: 
jb302@29: void
jb302@29: set_reg(BYTE reg, BYTE val) {
jb302@29:     if (reg < 4) {
jb302@29:         regs[reg | (get_flag(BS) << 3)] = val;
jb302@29:     }
jb302@29:     else {
jb302@29:         switch (reg) {
jb302@29:             
jb302@29:             case 4:
jb302@29:                 regs[DPH] = val;
jb302@29:                 break;
jb302@29:             case 5:
jb302@29:                 regs[DPL] = val;
jb302@29:                 break;
jb302@29:             case 6:
jb302@29:                 regs[SPH] = val;
jb302@29:                 break;
jb302@29:             case 7:
jb302@29:                 regs[SPL] = val;
jb302@29:                 break;
jb302@29:             default:
jb302@29:                 break;
jb302@29:         }
jb302@29:     }
jb302@29: }