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Hopefully fix decimal mode handling. Hopefully.

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This commit is contained in:
Radosław Kujawa 2017-02-12 22:56:07 +01:00
parent ce5330dfac
commit 23105b4861
1 changed files with 47 additions and 12 deletions
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59
src/emulation.c
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@ -9,8 +9,8 @@ static void emul_smb(rk65c02emu_t *, void *, instruction_t *, uint8_t);
static void emul_bbr(rk65c02emu_t *, void *, instruction_t *, uint8_t);
static void emul_bbs(rk65c02emu_t *, void *, instruction_t *, uint8_t);
/* Convert 8-bit binary value into binary coded decimal. */
static inline uint8_t to_bcd(uint8_t val)
/* Convert 8-bit BCD to binary value. */
static inline uint8_t from_bcd(uint8_t val)
{
uint8_t rv;
@ -20,6 +20,24 @@ static inline uint8_t to_bcd(uint8_t val)
return rv;
}
/* Convert 8-bit binary to BCD value. */
static inline uint8_t to_bcd(uint8_t val)
{
uint16_t shift, digit;
uint8_t bcd;
shift = 0;
bcd = 0;
while (val > 0) {
digit = val % 10;
bcd += (digit << shift);
shift += 4;
val /= 10;
}
return bcd;
}
/*
* Implementation of emulation of instructions follows below.
*/
@ -33,7 +51,7 @@ emul_adc(rk65c02emu_t *e, void *id, instruction_t *i)
arg = instruction_data_read_1(e, (instrdef_t *) id, i);
if (e->regs.P & P_DECIMAL)
res = to_bcd(e->regs.A) + to_bcd(arg);
res = from_bcd(e->regs.A) + from_bcd(arg);
else
res = e->regs.A + arg;
@ -45,21 +63,25 @@ emul_adc(rk65c02emu_t *e, void *id, instruction_t *i)
else
e->regs.P &= ~P_SIGN_OVERFLOW;
if (e->regs.P & P_DECIMAL)
if (e->regs.P & P_DECIMAL) {
/* if the result does not fit into two BCD digits then set carry */
if (res > 99)
e->regs.P |= P_CARRY;
else
e->regs.P &= ~P_CARRY;
else
} else {
/* if the result does not fit into 8 bits then set carry */
if (res > 0xFF)
e->regs.P |= P_CARRY;
else
e->regs.P &= ~P_CARRY;
}
/* squash the result into accumulator's 8 bits, lol */
e->regs.A = (uint8_t) res;
if (e->regs.P & P_DECIMAL)
e->regs.A = to_bcd(res);
else
e->regs.A = (uint8_t) res;
instruction_status_adjust_zero(e, e->regs.A);
instruction_status_adjust_negative(e, e->regs.A);
@ -820,7 +842,10 @@ emul_sbc(rk65c02emu_t *e, void *id, instruction_t *i)
uint16_t res; /* meh */
arg = instruction_data_read_1(e, (instrdef_t *) id, i);
res = e->regs.A - arg;
if (e->regs.P & P_DECIMAL)
res = from_bcd(e->regs.A) - from_bcd(arg);
else
res = e->regs.A - arg;
/* if the carry flag is NOT set then "borrow" */
if (!(e->regs.P & P_CARRY))
@ -831,14 +856,24 @@ emul_sbc(rk65c02emu_t *e, void *id, instruction_t *i)
else
e->regs.P &= ~P_SIGN_OVERFLOW;
/* if the result does not fit into 8 bits then clear carry */
if (res & 0x8000)
e->regs.P &= ~P_CARRY;
if (e->regs.P & P_DECIMAL)
if ((res > 99) || (res < 0))
e->regs.P |= P_CARRY;
else
e->regs.P &= ~P_CARRY;
else
e->regs.P |= P_CARRY;
/* if the result does not fit into 8 bits then clear carry */
if (res & 0x8000)
e->regs.P &= ~P_CARRY;
else
e->regs.P |= P_CARRY;
/* squash the result into accumulator's 8 bits, lol */
e->regs.A = (uint8_t) res;
if (e->regs.P & P_DECIMAL)
e->regs.A = to_bcd(res);
else
e->regs.A = (uint8_t) res;
instruction_status_adjust_zero(e, e->regs.A);
instruction_status_adjust_negative(e, e->regs.A);