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Fixes #40 - Missing Decimal support for ADC/SBC

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This commit is contained in:
Stefan Arentz 2016-11-22 15:53:38 -05:00
parent eb9c0751a2
commit 2094597e34
1 changed files with 66 additions and 7 deletions
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73
ins.c
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@ -35,12 +35,38 @@ static void update_zn(struct cpu_t *cpu, uint8_t v) {
/* ADC */
static void adc(struct cpu_t *cpu, uint8_t m) {
uint16_t t = (uint16_t)cpu->state.a + (uint16_t)m + (uint16_t)(cpu->state.c ? 1 : 0);
uint8_t r = (uint8_t) (t & 0xff);
cpu->state.c = (t & 0x0100) != 0;
cpu->state.v = (cpu->state.a^r) & (m^r) & 0x80;
cpu->state.a = r;
update_zn(cpu, cpu->state.a);
uint8_t c = cpu->state.c ? 1 : 0;
if (cpu->state.d) {
uint8_t cb = 0;
uint8_t low = (cpu->state.a & 0x0f) + (m & 0x0f) + c;
if ((low & 0xff) > 9) {
low += 6;
}
if (low > 15) {
cb = 1;
}
uint8_t high = (cpu->state.a >> 4) + (m >> 4) + cb;
if ((high & 0xff) > 9) {
high += 6;
}
uint8_t r = (low & 0x0F) | ((high<<4)&0xF0);
cpu->state.c = (high > 15);
cpu->state.z = (r == 0);
cpu->state.n = 0;
cpu->state.v = 0;
cpu->state.a = r;
} else {
uint16_t t = (uint16_t)cpu->state.a + (uint16_t)m + (uint16_t)c;
uint8_t r = (int8_t)t;
cpu->state.c = (t & 0x0100) != 0;
cpu->state.v = (cpu->state.a^r) & (m^r) & 0x80;
cpu->state.a = r;
update_zn(cpu, cpu->state.a);
}
}
static void adc_imm(struct cpu_t *cpu, uint8_t oper) {
@ -705,7 +731,40 @@ static void rts(struct cpu_t *cpu) {
/* SBC */
static void sbc(struct cpu_t *cpu, uint8_t m) {
adc(cpu, m ^ 0xff);
uint8_t c = cpu->state.c ? 1 : 0;
if (cpu->state.d) {
uint8_t cb = 0;
if (c == 0) {
c = 1;
} else {
c = 0;
}
uint8_t low = (cpu->state.a & 0x0F) - (m & 0x0F) - c;
if ((low & 0x10) != 0) {
low -= 6;
}
if ((low & 0x10) != 0) {
cb = 1;
}
uint8_t high = (cpu->state.a >> 4) - (m >> 4) - cb;
if ((high & 0x10) != 0) {
high -= 6;
}
int8_t result = (low & 0x0F) | (high << 4);
cpu->state.c = (high & 0xff) < 15;
cpu->state.z = (result == 0);
cpu->state.n = 0;
cpu->state.v = 0;
cpu->state.a = result;
} else {
adc(cpu, m ^ 0xff);
}
}
static void sbc_imm(struct cpu_t *cpu, uint8_t oper) {