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Eliminate SBCD macro.

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This commit is contained in:
Thomas Harte 2022-10-17 15:12:38 -04:00
parent aff1caed15
commit ee3a3df0b5
1 changed files with 28 additions and 33 deletions
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61
InstructionSets/M68k/Implementation/PerformImplementation.hpp
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@ -71,6 +71,28 @@ static void add_sub(IntT source, IntT &destination, Status &status) {
destination = result;
}
inline void sbcd(uint8_t rhs, uint8_t lhs, uint8_t &destination, Status &status) {
const int extend = (status.extend_flag ? 1 : 0);
const int unadjusted_result = lhs - rhs - extend;
const int top = (lhs & 0xf0) - (rhs & 0xf0) - (0x60 & (unadjusted_result >> 4));
int result = (lhs & 0xf) - (rhs & 0xf) - extend;
const int low_adjustment = 0x06 & (result >> 4);
status.extend_flag = status.carry_flag = Status::FlagT(
(unadjusted_result - low_adjustment) & 0x300
);
result = result + top - low_adjustment;
/* Store the result. */
destination = uint8_t(result);
/* Set all remaining flags essentially as if this were normal subtraction. */
status.zero_result |= destination;
status.negative_flag = result & 0x80;
status.overflow_flag = unadjusted_result & ~result & 0x80;
}
/// Performs a compare of @c source to @c destination, setting zero, carry, negative and overflow flags.
template <typename IntT>
static void compare(IntT source, IntT destination, Status &status) {
@ -765,48 +787,21 @@ template <
status.overflow_flag = status.carry_flag = 0;
break;
#define sbcd(d) \
const int extend = (status.extend_flag ? 1 : 0); \
const int unadjusted_result = destination - source - extend; \
\
const int top = (destination & 0xf0) - (source & 0xf0) - (0x60 & (unadjusted_result >> 4)); \
\
int result = (destination & 0xf) - (source & 0xf) - extend; \
const int low_adjustment = 0x06 & (result >> 4); \
status.extend_flag = status.carry_flag = Status::FlagT( \
(unadjusted_result - low_adjustment) & 0x300 \
); \
result = result + top - low_adjustment; \
\
/* Store the result. */ \
d = uint8_t(result); \
\
/* Set all remaining flags essentially as if this were normal subtraction. */ \
status.zero_result |= d; \
status.negative_flag = result & 0x80; \
status.overflow_flag = unadjusted_result & ~result & 0x80; \
/*
SBCD subtracts the lowest byte of the source from that of the destination using
BCD arithmetic, obeying the extend flag.
*/
case Operation::SBCD: {
const uint8_t source = src.b;
const uint8_t destination = dest.b;
sbcd(dest.b);
} break;
case Operation::SBCD:
Primitive::sbcd(src.b, dest.b, dest.b, status);
break;
/*
NBCD is like SBCD except that the result is 0 - source rather than
destination - source.
*/
case Operation::NBCD: {
const uint8_t source = src.b;
const uint8_t destination = 0;
sbcd(src.b);
} break;
#undef sbcd
case Operation::NBCD:
Primitive::sbcd(src.b, 0, src.b, status);
break;
// EXG and SWAP exchange/swap words or long words.