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unpacked: Use ResidualErrorOnRightShift in FPRoundBase

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Fixes a bug relating to exponents that are severely out of range.
This commit is contained in:
MerryMage 2018-07-23 17:41:13 +01:00
parent 805428e35e
commit f17cd6f2c5
2 changed files with 24 additions and 13 deletions
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25
src/common/fp/unpacked.cpp
View file

@ -6,6 +6,7 @@
#include "common/fp/fpsr.h" #include "common/fp/fpsr.h"
#include "common/fp/info.h" #include "common/fp/info.h"
#include "common/fp/mantissa_util.h"
#include "common/fp/process_exception.h" #include "common/fp/process_exception.h"
#include "common/fp/rounding_mode.h" #include "common/fp/rounding_mode.h"
#include "common/fp/unpacked.h" #include "common/fp/unpacked.h"
@ -55,11 +56,11 @@ template std::tuple<FPType, bool, FPUnpacked> FPUnpack<u32>(u32 op, FPCR fpcr, F
template std::tuple<FPType, bool, FPUnpacked> FPUnpack<u64>(u64 op, FPCR fpcr, FPSR& fpsr); template std::tuple<FPType, bool, FPUnpacked> FPUnpack<u64>(u64 op, FPCR fpcr, FPSR& fpsr);
template<size_t F> template<size_t F>
std::tuple<bool, int, u64, u64> Normalize(FPUnpacked op) { std::tuple<bool, int, u64, ResidualError> Normalize(FPUnpacked op, int extra_right_shift = 0) {
const int highest_set_bit = Common::HighestSetBit(op.mantissa); const int highest_set_bit = Common::HighestSetBit(op.mantissa);
const int shift_amount = highest_set_bit - static_cast<int>(F); const int shift_amount = highest_set_bit - static_cast<int>(F) + extra_right_shift;
const u64 mantissa = Safe::LogicalShiftRight(op.mantissa, shift_amount); const u64 mantissa = Safe::LogicalShiftRight(op.mantissa, shift_amount);
const u64 error = Safe::LogicalShiftRightDouble(op.mantissa, static_cast<u64>(0), shift_amount); const ResidualError error = ResidualErrorOnRightShift(op.mantissa, shift_amount);
const int exponent = op.exponent + highest_set_bit; const int exponent = op.exponent + highest_set_bit;
return std::make_tuple(op.sign, exponent, mantissa, error); return std::make_tuple(op.sign, exponent, mantissa, error);
} }
@ -83,28 +84,26 @@ FPT FPRoundBase(FPUnpacked op, FPCR fpcr, RoundingMode rounding, FPSR& fpsr) {
int biased_exp = std::max<int>(exponent - minimum_exp + 1, 0); int biased_exp = std::max<int>(exponent - minimum_exp + 1, 0);
if (biased_exp == 0) { if (biased_exp == 0) {
error = Safe::LogicalShiftRightDouble(mantissa, error, minimum_exp - exponent); std::tie(sign, exponent, mantissa, error) = Normalize<F>(op, minimum_exp - exponent);
mantissa = Safe::LogicalShiftRight(mantissa, minimum_exp - exponent);
} }
if (biased_exp == 0 && (error != 0 || fpcr.UFE())) { if (biased_exp == 0 && (error != ResidualError::Zero || fpcr.UFE())) {
FPProcessException(FPExc::Underflow, fpcr, fpsr); FPProcessException(FPExc::Underflow, fpcr, fpsr);
} }
bool round_up = false, overflow_to_inf = false; bool round_up = false, overflow_to_inf = false;
switch (rounding) { switch (rounding) {
case RoundingMode::ToNearest_TieEven: { case RoundingMode::ToNearest_TieEven: {
constexpr u64 half = static_cast<u64>(1) << (Common::BitSize<u64>() - 1); round_up = (error > ResidualError::Half) || (error == ResidualError::Half && Common::Bit<0>(mantissa));
round_up = (error > half) || (error == half && Common::Bit<0>(mantissa));
overflow_to_inf = true; overflow_to_inf = true;
break; break;
} }
case RoundingMode::TowardsPlusInfinity: case RoundingMode::TowardsPlusInfinity:
round_up = error != 0 && !sign; round_up = error != ResidualError::Zero && !sign;
overflow_to_inf = !sign; overflow_to_inf = !sign;
break; break;
case RoundingMode::TowardsMinusInfinity: case RoundingMode::TowardsMinusInfinity:
round_up = error != 0 && sign; round_up = error != ResidualError::Zero && sign;
overflow_to_inf = sign; overflow_to_inf = sign;
break; break;
default: default:
@ -128,7 +127,7 @@ FPT FPRoundBase(FPUnpacked op, FPCR fpcr, RoundingMode rounding, FPSR& fpsr) {
} }
} }
if (error != 0 && rounding == RoundingMode::ToOdd) { if (error != ResidualError::Zero && rounding == RoundingMode::ToOdd) {
mantissa = Common::ModifyBit<0>(mantissa, true); mantissa = Common::ModifyBit<0>(mantissa, true);
} }
@ -152,7 +151,7 @@ FPT FPRoundBase(FPUnpacked op, FPCR fpcr, RoundingMode rounding, FPSR& fpsr) {
result += biased_exp; result += biased_exp;
result <<= F; result <<= F;
result |= static_cast<FPT>(mantissa) & FPInfo<FPT>::mantissa_mask; result |= static_cast<FPT>(mantissa) & FPInfo<FPT>::mantissa_mask;
if (error != 0) { if (error != ResidualError::Zero) {
FPProcessException(FPExc::Inexact, fpcr, fpsr); FPProcessException(FPExc::Inexact, fpcr, fpsr);
} }
} }
@ -167,7 +166,7 @@ FPT FPRoundBase(FPUnpacked op, FPCR fpcr, RoundingMode rounding, FPSR& fpsr) {
result += biased_exp; result += biased_exp;
result <<= F; result <<= F;
result |= static_cast<FPT>(mantissa) & FPInfo<FPT>::mantissa_mask; result |= static_cast<FPT>(mantissa) & FPInfo<FPT>::mantissa_mask;
if (error != 0) { if (error != ResidualError::Zero) {
FPProcessException(FPExc::Inexact, fpcr, fpsr); FPProcessException(FPExc::Inexact, fpcr, fpsr);
} }
} }

12
tests/fp/unpacked_tests.cpp
View file

@ -75,3 +75,15 @@ TEST_CASE("FPUnpack<->FPRound Round-trip Tests", "[fp]") {
REQUIRE(input == output); REQUIRE(input == output);
} }
} }
TEST_CASE("FPRound (near zero, round to posinf)", "[fp]") {
const FPUnpacked input = {false, -353, 0x0a98d25ace5b2000};
FPSR fpsr;
FPCR fpcr;
fpcr.RMode(RoundingMode::TowardsPlusInfinity);
const u32 output = FPRound<u32>(input, fpcr, fpsr);
REQUIRE(output == 0x00000001);
}