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Repattern DIVS after DIVU.

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This commit is contained in:
Thomas Harte 2022-05-15 16:54:58 -04:00
parent 20a191f144
commit 341bf2e480
1 changed files with 16 additions and 28 deletions
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44
InstructionSets/M68k/Implementation/PerformImplementation.hpp
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@ -532,22 +532,22 @@ template <
return; return;
} }
uint32_t dividend = dest.l; const auto dividend = uint32_t(dest.l);
uint32_t divisor = src.w; const auto divisor = uint32_t(uint16_t(src.w));
const auto quotient = dividend / divisor; const auto quotient = dividend / divisor;
// If overflow would occur, appropriate flags are set and the result is not written back. // If overflow would occur, appropriate flags are set and the result is not written back.
if(quotient > 65535) { if(quotient != uint16_t(quotient)) {
status.overflow_flag = status.zero_result = status.negative_flag = 1; status.overflow_flag = 1;
flow_controller.template did_divu<true>(dividend, divisor); flow_controller.template did_divu<true>(dividend, divisor);
return; return;
} }
const uint16_t remainder = uint16_t(dividend % divisor); const auto remainder = uint16_t(dividend % divisor);
dest.l = uint32_t((remainder << 16) | uint16_t(quotient)); dest.l = uint32_t((remainder << 16) | uint16_t(quotient));
status.overflow_flag = 0; status.overflow_flag = 0;
status.zero_result = quotient; status.zero_result = Status::FlagT(quotient);
status.negative_flag = status.zero_result & 0x8000; status.negative_flag = status.zero_result & 0x8000;
flow_controller.template did_divu<false>(dividend, divisor); flow_controller.template did_divu<false>(dividend, divisor);
} break; } break;
@ -562,36 +562,24 @@ template <
break; break;
} }
const int32_t signed_dividend = int32_t(dest.l); const auto dividend = int32_t(dest.l);
const int32_t signed_divisor = s_extend16(src.w); const auto divisor = int32_t(int16_t(src.w));
const auto result_sign = const auto quotient = dividend / divisor;
( (0 <= signed_dividend) - (signed_dividend < 0) ) *
( (0 <= signed_divisor) - (signed_divisor < 0) );
const uint32_t dividend = uint32_t(std::abs(signed_dividend));
const uint32_t divisor = uint32_t(std::abs(signed_divisor));
int cycles_expended = 12; // Covers the nn nnn n to get beyond the sign test.
if(signed_dividend < 0) {
cycles_expended += 2; // An additional microycle applies if the dividend is negative.
}
// Check for overflow. If it exists, work here is already done. // Check for overflow. If it exists, work here is already done.
const auto quotient = dividend / divisor; if(quotient != int16_t(quotient)) {
if(quotient > 32767) {
status.overflow_flag = 1; status.overflow_flag = 1;
flow_controller.template did_divs<true>(signed_dividend, signed_divisor); flow_controller.template did_divs<true>(dividend, divisor);
break; break;
} }
const uint16_t remainder = uint16_t(signed_dividend % signed_divisor); const auto remainder = uint16_t(dividend % divisor);
const int signed_quotient = result_sign*int(quotient); dest.l = uint32_t((remainder << 16) | uint16_t(quotient));
dest.l = uint32_t((remainder << 16) | uint16_t(signed_quotient));
status.zero_result = Status::FlagT(signed_quotient);
status.negative_flag = status.zero_result & 0x8000;
status.overflow_flag = 0; status.overflow_flag = 0;
flow_controller.template did_divs<false>(signed_dividend, signed_divisor); status.zero_result = Status::FlagT(quotient);
status.negative_flag = status.zero_result & 0x8000;
flow_controller.template did_divs<false>(dividend, divisor);
} break; } break;
#undef announce_divide_by_zero #undef announce_divide_by_zero