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Remove modify_status() function

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Also rewrite tests to use macros
This commit is contained in:
Peter Evans 2018-02-28 21:40:52 -06:00
parent 8d0cf264d7
commit f8bda4ebd3
3 changed files with 6 additions and 64 deletions
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1
include/mos6502.h
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@ -172,7 +172,6 @@ extern vm_8bit mos6502_pop_stack(mos6502 *);
extern void mos6502_execute(mos6502 *);
extern void mos6502_free(mos6502 *);
extern void mos6502_last_executed(mos6502 *, vm_8bit *, vm_8bit *, vm_16bit *);
extern void mos6502_modify_status(mos6502 *, vm_8bit, int, int);
extern void mos6502_push_stack(mos6502 *, vm_8bit);
extern void mos6502_set(mos6502 *, size_t, vm_8bit);
extern void mos6502_set16(mos6502 *, size_t, vm_16bit);

52
src/mos6502.c
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@ -237,58 +237,6 @@ mos6502_set_status(mos6502 *cpu, vm_8bit status)
cpu->P = status;
}
/*
* In contrast, the modify_status function will conditionally set the
* contents of certain bits, based upon the value of the operand. Those
* bits are the negative, overflow, carry, and zero flags.
*/
void
mos6502_modify_status(mos6502 *cpu, vm_8bit status, int orig, int result)
{
int bit7o, bit7r;
if (status & MOS_NEGATIVE) {
cpu->P &= ~MOS_NEGATIVE;
if (result & 0x80) {
cpu->P |= MOS_NEGATIVE;
}
}
if (status & MOS_OVERFLOW) {
cpu->P &= ~MOS_OVERFLOW;
bit7o = orig & 0x80;
bit7r = result & 0x80;
// If the result of the operation is such that the sign bit,
// that is to say bit 7, changes, then we have overflowed. E.g.:
// 90 + 40 = 130, but that's actually -124 in two's complement.
// So if you are paying attention to the sign, you have
// overflowed from a positive into a negative result.
if (bit7o ^ bit7r) {
cpu->P |= MOS_OVERFLOW;
}
}
if (status & MOS_CARRY) {
cpu->P &= ~MOS_CARRY;
// The result of the operation requires 9 bits to hold, but we
// can only hold 8 bits; rather than lose that bit's value, it
// is held in the carry bit of the P register.
if (result > 0xFF) {
cpu->P |= MOS_CARRY;
}
}
if (status & MOS_ZERO) {
cpu->P &= ~MOS_ZERO;
if ((result & 0xff) == 0) {
cpu->P |= MOS_ZERO;
}
}
}
/*
* Return the instruction that is mapped to a given opcode.
*/

17
tests/mos6502.c
View File

@ -37,24 +37,19 @@ Test(mos6502, pop_stack)
Test(mos6502, modify_status)
{
mos6502_modify_status(cpu, MOS_NEGATIVE, 130, 130);
MOS_CHECK_N(130);
cr_assert_eq(cpu->P & MOS_NEGATIVE, MOS_NEGATIVE);
mos6502_modify_status(cpu, MOS_NEGATIVE, 123, 123);
MOS_CHECK_N(123);
cr_assert_neq(cpu->P & MOS_NEGATIVE, MOS_NEGATIVE);
mos6502_modify_status(cpu, MOS_OVERFLOW, 123, 133);
MOS_CHECK_V(123, 133);
cr_assert_eq(cpu->P & MOS_OVERFLOW, MOS_OVERFLOW);
mos6502_modify_status(cpu, MOS_OVERFLOW, 44, 44);
MOS_CHECK_V(44, 44);
cr_assert_neq(cpu->P & MOS_OVERFLOW, MOS_OVERFLOW);
mos6502_modify_status(cpu, MOS_CARRY, 230, 260);
cr_assert_eq(cpu->P & MOS_CARRY, MOS_CARRY);
mos6502_modify_status(cpu, MOS_CARRY, 30, 190);
cr_assert_neq(cpu->P & MOS_CARRY, MOS_CARRY);
mos6502_modify_status(cpu, MOS_ZERO, 0, 0);
MOS_CHECK_Z(0);
cr_assert_eq(cpu->P & MOS_ZERO, MOS_ZERO);
mos6502_modify_status(cpu, MOS_ZERO, 1, 1);
MOS_CHECK_Z(1);
cr_assert_neq(cpu->P & MOS_ZERO, MOS_ZERO);
}