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kroeningkroening
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ieee_floatt: introduce NOT_SET rounding mode
This adds a new rounding mode to ieee_floatt, NOT_SET, which is the default when constructing the object without rounding mode. Operations that require a rounding mode fail when the rounding mode is NOT_SET.
1 parent c4aaafd commit 24c2905

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6 files changed

+82
-27
lines changed

6 files changed

+82
-27
lines changed

‎src/ansi-c/literals/convert_float_literal.cpp

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -71,7 +71,9 @@ exprt convert_float_literal(const std::string &src)
7171
// but these aren't handled anywhere
7272
}
7373

74-
ieee_floatt a(type);
74+
// Compile-time rounding is implementation defined.
75+
// The choice below is arbitrary.
76+
ieee_floatt a(type, ieee_floatt::rounding_modet::ROUND_TO_EVEN);
7577

7678
if(parsed_float.exponent_base==10)
7779
a.from_base10(parsed_float.significand, parsed_float.exponent);

‎src/solvers/floatbv/float_utils.h

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -41,6 +41,9 @@ class float_utilst
4141

4242
switch(mode)
4343
{
44+
case ieee_floatt::NOT_SET:
45+
PRECONDITION(false);
46+
4447
case ieee_floatt::ROUND_TO_EVEN:
4548
round_to_even=const_literal(true);
4649
break;

‎src/util/ieee_float.cpp

Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -474,6 +474,8 @@ void ieee_floatt::build(
474474
const mp_integer &_fraction,
475475
const mp_integer &_exponent)
476476
{
477+
PRECONDITION(rounding_mode != rounding_modet::NOT_SET);
478+
477479
sign_flag=_fraction<0;
478480
fraction=_fraction;
479481
if(sign_flag)
@@ -488,6 +490,8 @@ void ieee_floatt::from_base10(
488490
const mp_integer &_fraction,
489491
const mp_integer &_exponent)
490492
{
493+
PRECONDITION(rounding_mode != rounding_modet::NOT_SET);
494+
491495
NaN_flag=infinity_flag=false;
492496
sign_flag=_fraction<0;
493497
fraction=_fraction;
@@ -584,6 +588,9 @@ void ieee_floatt::align()
584588
// we need to consider the rounding mode here
585589
switch(rounding_mode)
586590
{
591+
case NOT_SET:
592+
PRECONDITION(false);
593+
587594
case UNKNOWN:
588595
case NONDETERMINISTIC:
589596
case ROUND_TO_EVEN:
@@ -660,6 +667,9 @@ void ieee_floatt::divide_and_round(
660667
{
661668
switch(rounding_mode)
662669
{
670+
case NOT_SET:
671+
PRECONDITION(false);
672+
663673
case ROUND_TO_EVEN:
664674
{
665675
mp_integer divisor_middle = divisor / 2;
@@ -708,6 +718,7 @@ constant_exprt ieee_floatt::to_expr() const
708718
ieee_floatt &ieee_floatt::operator/=(const ieee_floatt &other)
709719
{
710720
PRECONDITION(other.spec.f == spec.f);
721+
PRECONDITION(rounding_mode != rounding_modet::NOT_SET);
711722

712723
// NaN/x = NaN
713724
if(NaN_flag)
@@ -782,6 +793,7 @@ ieee_floatt &ieee_floatt::operator/=(const ieee_floatt &other)
782793
ieee_floatt &ieee_floatt::operator*=(const ieee_floatt &other)
783794
{
784795
PRECONDITION(other.spec.f == spec.f);
796+
PRECONDITION(rounding_mode != rounding_modet::NOT_SET);
785797

786798
if(other.NaN_flag)
787799
make_NaN();
@@ -818,6 +830,8 @@ ieee_floatt &ieee_floatt::operator*=(const ieee_floatt &other)
818830
ieee_floatt &ieee_floatt::operator+=(const ieee_floatt &other)
819831
{
820832
PRECONDITION(other.spec == spec);
833+
PRECONDITION(rounding_mode != rounding_modet::NOT_SET);
834+
821835
ieee_floatt _other=other;
822836

823837
if(other.NaN_flag)
@@ -1058,6 +1072,8 @@ bool ieee_floatt::ieee_not_equal(const ieee_floatt &other) const
10581072

10591073
void ieee_floatt::change_spec(const ieee_float_spect &dest_spec)
10601074
{
1075+
PRECONDITION(rounding_mode != rounding_modet::NOT_SET);
1076+
10611077
mp_integer _exponent=exponent-spec.f;
10621078
mp_integer _fraction=fraction;
10631079

‎src/util/ieee_float.h

Lines changed: 50 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -121,22 +121,29 @@ class ieee_floatt
121121
// what is recommended in C11 5.2.4.2.2
122122
enum rounding_modet
123123
{
124-
ROUND_TO_EVEN=0, ROUND_TO_MINUS_INF=1,
125-
ROUND_TO_PLUS_INF=2, ROUND_TO_ZERO=3,
126-
UNKNOWN, NONDETERMINISTIC
124+
ROUND_TO_EVEN = 0,
125+
ROUND_TO_MINUS_INF = 1,
126+
ROUND_TO_PLUS_INF = 2,
127+
ROUND_TO_ZERO = 3,
128+
UNKNOWN,
129+
NONDETERMINISTIC,
130+
NOT_SET
127131
};
128132

129133
// A helper to turn a rounding mode into a constant bitvector expression
130134
static constant_exprt rounding_mode_expr(rounding_modet);
131135

132-
rounding_modet rounding_mode;
136+
rounding_modet rounding_mode = rounding_modet::NOT_SET;
133137

134138
ieee_float_spect spec;
135139

136-
explicit ieee_floatt(const ieee_float_spect &_spec):
137-
rounding_mode(ROUND_TO_EVEN),
138-
spec(_spec), sign_flag(false), exponent(0), fraction(0),
139-
NaN_flag(false), infinity_flag(false)
140+
explicit ieee_floatt(const ieee_float_spect &_spec)
141+
: spec(_spec),
142+
sign_flag(false),
143+
exponent(0),
144+
fraction(0),
145+
NaN_flag(false),
146+
infinity_flag(false)
140147
{
141148
}
142149

@@ -151,26 +158,47 @@ class ieee_floatt
151158
{
152159
}
153160

154-
explicit ieee_floatt(const floatbv_typet &type):
155-
rounding_mode(ROUND_TO_EVEN),
156-
spec(ieee_float_spect(type)),
157-
sign_flag(false),
158-
exponent(0),
159-
fraction(0),
160-
NaN_flag(false),
161-
infinity_flag(false)
161+
explicit ieee_floatt(const floatbv_typet &type)
162+
: spec(ieee_float_spect(type)),
163+
sign_flag(false),
164+
exponent(0),
165+
fraction(0),
166+
NaN_flag(false),
167+
infinity_flag(false)
162168
{
163169
}
164170

165-
ieee_floatt():
166-
rounding_mode(ROUND_TO_EVEN),
167-
sign_flag(false), exponent(0), fraction(0),
168-
NaN_flag(false), infinity_flag(false)
171+
explicit ieee_floatt(
172+
const floatbv_typet &type,
173+
rounding_modet __rounding_mode)
174+
: rounding_mode(__rounding_mode),
175+
spec(ieee_float_spect(type)),
176+
sign_flag(false),
177+
exponent(0),
178+
fraction(0),
179+
NaN_flag(false),
180+
infinity_flag(false)
169181
{
170182
}
171183

172-
explicit ieee_floatt(const constant_exprt &expr):
173-
rounding_mode(ROUND_TO_EVEN)
184+
ieee_floatt()
185+
: sign_flag(false),
186+
exponent(0),
187+
fraction(0),
188+
NaN_flag(false),
189+
infinity_flag(false)
190+
{
191+
}
192+
193+
explicit ieee_floatt(const constant_exprt &expr)
194+
{
195+
from_expr(expr);
196+
}
197+
198+
explicit ieee_floatt(
199+
const constant_exprt &expr,
200+
rounding_modet __rounding_mode)
201+
: rounding_mode(__rounding_mode)
174202
{
175203
from_expr(expr);
176204
}

‎src/util/simplify_expr.cpp

Lines changed: 8 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -70,6 +70,7 @@ simplify_exprt::resultt<> simplify_exprt::simplify_abs(const abs_exprt &expr)
7070

7171
if(type.id()==ID_floatbv)
7272
{
73+
// Does not need rounding
7374
ieee_floatt value(to_constant_expr(to_unary_expr(expr).op()));
7475
value.set_sign(false);
7576
return value.to_expr();
@@ -104,6 +105,7 @@ simplify_exprt::resultt<> simplify_exprt::simplify_sign(const sign_exprt &expr)
104105

105106
if(type.id()==ID_floatbv)
106107
{
108+
// Does not need rounding
107109
ieee_floatt value(to_constant_expr(expr.op()));
108110
return make_boolean_expr(value.get_sign());
109111
}
@@ -1179,7 +1181,7 @@ simplify_exprt::simplify_typecast(const typecast_exprt &expr)
11791181
const floatbv_typet &f_expr_type=
11801182
to_floatbv_type(expr_type);
11811183

1182-
ieee_floatt f(f_expr_type);
1184+
ieee_floatt f(f_expr_type, ieee_floatt::rounding_modet::ROUND_TO_EVEN);
11831185
f.from_integer(int_value);
11841186

11851187
return f.to_expr();
@@ -1215,7 +1217,9 @@ simplify_exprt::simplify_typecast(const typecast_exprt &expr)
12151217
}
12161218
else if(op_type_id==ID_floatbv)
12171219
{
1218-
ieee_floatt f(to_constant_expr(expr.op()));
1220+
ieee_floatt f{
1221+
to_constant_expr(expr.op()),
1222+
ieee_floatt::rounding_modet::ROUND_TO_EVEN};
12191223

12201224
if(expr_type_id==ID_unsignedbv ||
12211225
expr_type_id==ID_signedbv)
@@ -1233,7 +1237,7 @@ simplify_exprt::simplify_typecast(const typecast_exprt &expr)
12331237
{
12341238
fixedbvt fixedbv;
12351239
fixedbv.spec=fixedbv_spect(to_fixedbv_type(expr_type));
1236-
ieee_floatt factor(f.spec);
1240+
ieee_floatt factor(f.spec, ieee_floatt::rounding_modet::ROUND_TO_EVEN);
12371241
factor.from_integer(power(2, fixedbv.spec.get_fraction_bits()));
12381242
f*=factor;
12391243
fixedbv.set_value(f.to_integer());
@@ -1267,6 +1271,7 @@ simplify_exprt::simplify_typecast(const typecast_exprt &expr)
12671271
{
12681272
const auto width = to_bv_type(op_type).get_width();
12691273
const auto int_value = bvrep2integer(value, width, false);
1274+
// Does not need rounding.
12701275
ieee_floatt ieee_float{to_floatbv_type(expr_type)};
12711276
ieee_float.unpack(int_value);
12721277
return ieee_float.to_expr();

‎src/util/simplify_expr_int.cpp

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1889,7 +1889,8 @@ simplify_exprt::resultt<> simplify_exprt::simplify_inequality_rhs_is_constant(
18891889
expr.op0().id() == ID_typecast && expr.op0().type().id() == ID_floatbv &&
18901890
to_typecast_expr(expr.op0()).op().type().id() == ID_floatbv)
18911891
{
1892-
ieee_floatt const_val(to_constant_expr(expr.op1()));
1892+
ieee_floatt const_val{
1893+
to_constant_expr(expr.op1()), ieee_floatt::rounding_modet::ROUND_TO_EVEN};
18931894
ieee_floatt const_val_converted=const_val;
18941895
const_val_converted.change_spec(ieee_float_spect(
18951896
to_floatbv_type(to_typecast_expr(expr.op0()).op().type())));

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