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Fix right shifting of negative values in cpp_int.

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To give the same values as 2's complement representations,
though not the same bit-pattern.
Updated tests.
Fixed assignment from float to not rely on shifting negative values.
This commit is contained in:
jzmaddock
2015-05-30 11:39:39 +01:00
parent 3b41c0af07
commit f89bac311b
3 changed files with 49 additions and 2 deletions
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7
include/boost/multiprecision/cpp_int.hpp
View File

@@ -1224,6 +1224,13 @@ private:
using std::ldexp;
using std::floor;
if(a < 0)
{
do_assign_arithmetic(-a, mpl::false_());
this->sign(true);
return;
}
if (a == 0) {
*this = static_cast<limb_type>(0u);
}

36
include/boost/multiprecision/cpp_int/bitwise.hpp
View File

@@ -24,6 +24,22 @@ void is_valid_bitwise_op(
cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>&,
const cpp_int_backend<MinBits2, MaxBits2, SignType2, Checked2, Allocator2>& , const mpl::int_<unchecked>&){}
template <unsigned MinBits1, unsigned MaxBits1, cpp_int_check_type Checked1, class Allocator1>
void is_valid_bitwise_op(
const cpp_int_backend<MinBits1, MaxBits1, signed_magnitude, Checked1, Allocator1>& result, const mpl::int_<checked>&)
{
if(result.sign())
BOOST_THROW_EXCEPTION(std::range_error("Bitwise operations on negative values results in undefined behavior."));
}
template <unsigned MinBits1, unsigned MaxBits1, cpp_int_check_type Checked1, class Allocator1>
void is_valid_bitwise_op(
const cpp_int_backend<MinBits1, MaxBits1, unsigned_magnitude, Checked1, Allocator1>&, const mpl::int_<checked>&){}
template <unsigned MinBits1, unsigned MaxBits1, cpp_integer_type SignType1, cpp_int_check_type Checked1, class Allocator1>
void is_valid_bitwise_op(
cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>&, const mpl::int_<unchecked>&){}
template <class CppInt1, class CppInt2, class Op>
void bitwise_op(
CppInt1& result,
@@ -285,6 +301,7 @@ inline typename enable_if_c<!is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBit
cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>& result,
double_limb_type s) BOOST_NOEXCEPT_IF((is_non_throwing_cpp_int<cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1> >::value))
{
is_valid_bitwise_op(result, typename cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::checked_type());
if(!s)
return;
@@ -361,16 +378,24 @@ inline typename enable_if_c<!is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBit
cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>& result,
double_limb_type s) BOOST_NOEXCEPT_IF((is_non_throwing_cpp_int<cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1> >::value))
{
is_valid_bitwise_op(result, typename cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::checked_type());
if(!s)
return;
bool is_neg = result.sign();
if(is_neg)
eval_increment(result);
limb_type offset = static_cast<limb_type>(s / cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::limb_bits);
limb_type shift = static_cast<limb_type>(s % cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::limb_bits);
unsigned ors = result.size();
unsigned rs = ors;
if(offset >= rs)
{
result = limb_type(0);
if(is_neg)
result = signed_limb_type(-1);
else
result = limb_type(0);
return;
}
rs -= offset;
@@ -379,7 +404,10 @@ inline typename enable_if_c<!is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBit
--rs;
if(rs == 0)
{
result = limb_type(0);
if(is_neg)
result = signed_limb_type(-1);
else
result = limb_type(0);
return;
}
unsigned i = 0;
@@ -399,6 +427,8 @@ inline typename enable_if_c<!is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBit
pr[i] = pr[i + offset];
}
result.resize(rs, rs);
if(is_neg)
eval_decrement(result);
}
//
@@ -408,6 +438,7 @@ template <unsigned MinBits1, unsigned MaxBits1, cpp_integer_type SignType1, cpp_
BOOST_MP_FORCEINLINE typename enable_if<is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1> > >::type
eval_left_shift(cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>& result, T s) BOOST_NOEXCEPT_IF((is_non_throwing_cpp_int<cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1> >::value))
{
is_valid_bitwise_op(result, typename cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::checked_type());
*result.limbs() = detail::checked_left_shift(*result.limbs(), s, typename cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::checked_type());
result.normalize();
}
@@ -417,6 +448,7 @@ BOOST_MP_FORCEINLINE typename enable_if<is_trivial_cpp_int<cpp_int_backend<MinBi
eval_right_shift(cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>& result, T s) BOOST_NOEXCEPT_IF((is_non_throwing_cpp_int<cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1> >::value))
{
// Nothing to check here... just make sure we don't invoke undefined behavior:
is_valid_bitwise_op(result, typename cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::checked_type());
*result.limbs() = (static_cast<unsigned>(s) >= sizeof(*result.limbs()) * CHAR_BIT) ? 0 : *result.limbs() >> s;
}

8
test/test_cpp_int.cpp
View File

@@ -172,14 +172,22 @@ struct tester
if(!std::numeric_limits<test_type>::is_bounded)
{
BOOST_CHECK_EQUAL(mpz_int(a << i).str(), test_type(a1 << i).str());
BOOST_CHECK_EQUAL(mpz_int(-a << i).str(), test_type(-a1 << i).str());
}
else if(!is_checked_cpp_int<test_type>::value)
{
test_type t1(mpz_int(a << i).str());
test_type t2 = a1 << i;
BOOST_CHECK_EQUAL(t1, t2);
t1 = test_type(mpz_int(-a << i).str());
t2 = -a1 << i;
BOOST_CHECK_EQUAL(t1, t2);
}
BOOST_CHECK_EQUAL(mpz_int(a >> i).str(), test_type(a1 >> i).str());
if(!is_checked_cpp_int<test_type>::value)
{
BOOST_CHECK_EQUAL(mpz_int(-a >> i).str(), test_type(-a1 >> i).str());
}
}
// gcd/lcm
BOOST_CHECK_EQUAL(mpz_int(gcd(a, b)).str(), test_type(gcd(a1, b1)).str());