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[ruby/bigdecimal] Allow digits=0 in BigDecimal(flt) and Float#to_d

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Using dtoa of mode=0, we can determine the number of digits in decimal that is
necessary to represent the given Float number without errors.

This change permits digits=0 in BigDecimal(flt) and Float#to_d, and these
methods use dtoa of mode=0 when the given digits is 0.

Internal implicit conversion from Float also uses digits=0.

[Fix GH-70]

https://github.com/ruby/bigdecimal/commit/2dbe170e35
This commit is contained in:
Kenta Murata 2021-01-13 10:28:23 +09:00
parent 30f1316401
commit a5b4b806de
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GPG Key ID: CEFE8AFB6081B062
4 changed files with 40 additions and 25 deletions
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53
ext/bigdecimal/bigdecimal.c
View File

@ -947,7 +947,7 @@ BigDecimal_coerce(VALUE self, VALUE other)
Real *b;
if (RB_TYPE_P(other, T_FLOAT)) {
GUARD_OBJ(b, GetVpValueWithPrec(other, DBLE_FIG, 1));
GUARD_OBJ(b, GetVpValueWithPrec(other, 0, 1));
obj = rb_assoc_new(VpCheckGetValue(b), self);
}
else {
@ -1005,7 +1005,7 @@ BigDecimal_add(VALUE self, VALUE r)
GUARD_OBJ(a, GetVpValue(self, 1));
if (RB_TYPE_P(r, T_FLOAT)) {
b = GetVpValueWithPrec(r, DBLE_FIG, 1);
b = GetVpValueWithPrec(r, 0, 1);
}
else if (RB_TYPE_P(r, T_RATIONAL)) {
b = GetVpValueWithPrec(r, a->Prec*VpBaseFig(), 1);
@ -1063,7 +1063,7 @@ BigDecimal_sub(VALUE self, VALUE r)
GUARD_OBJ(a, GetVpValue(self,1));
if (RB_TYPE_P(r, T_FLOAT)) {
b = GetVpValueWithPrec(r, DBLE_FIG, 1);
b = GetVpValueWithPrec(r, 0, 1);
}
else if (RB_TYPE_P(r, T_RATIONAL)) {
b = GetVpValueWithPrec(r, a->Prec*VpBaseFig(), 1);
@ -1113,7 +1113,7 @@ BigDecimalCmp(VALUE self, VALUE r,char op)
break;
case T_FLOAT:
GUARD_OBJ(b, GetVpValueWithPrec(r, DBLE_FIG, 0));
GUARD_OBJ(b, GetVpValueWithPrec(r, 0, 0));
break;
case T_RATIONAL:
@ -1326,7 +1326,7 @@ BigDecimal_mult(VALUE self, VALUE r)
GUARD_OBJ(a, GetVpValue(self, 1));
if (RB_TYPE_P(r, T_FLOAT)) {
b = GetVpValueWithPrec(r, DBLE_FIG, 1);
b = GetVpValueWithPrec(r, 0, 1);
}
else if (RB_TYPE_P(r, T_RATIONAL)) {
b = GetVpValueWithPrec(r, a->Prec*VpBaseFig(), 1);
@ -1354,7 +1354,7 @@ BigDecimal_divide(Real **c, Real **res, Real **div, VALUE self, VALUE r)
GUARD_OBJ(a, GetVpValue(self, 1));
if (RB_TYPE_P(r, T_FLOAT)) {
b = GetVpValueWithPrec(r, DBLE_FIG, 1);
b = GetVpValueWithPrec(r, 0, 1);
}
else if (RB_TYPE_P(r, T_RATIONAL)) {
b = GetVpValueWithPrec(r, a->Prec*VpBaseFig(), 1);
@ -1420,7 +1420,7 @@ BigDecimal_DoDivmod(VALUE self, VALUE r, Real **div, Real **mod)
GUARD_OBJ(a, GetVpValue(self, 1));
if (RB_TYPE_P(r, T_FLOAT)) {
b = GetVpValueWithPrec(r, DBLE_FIG, 1);
b = GetVpValueWithPrec(r, 0, 1);
}
else if (RB_TYPE_P(r, T_RATIONAL)) {
b = GetVpValueWithPrec(r, a->Prec*VpBaseFig(), 1);
@ -1521,7 +1521,7 @@ BigDecimal_divremain(VALUE self, VALUE r, Real **dv, Real **rv)
GUARD_OBJ(a, GetVpValue(self, 1));
if (RB_TYPE_P(r, T_FLOAT)) {
b = GetVpValueWithPrec(r, DBLE_FIG, 1);
b = GetVpValueWithPrec(r, 0, 1);
}
else if (RB_TYPE_P(r, T_RATIONAL)) {
b = GetVpValueWithPrec(r, a->Prec*VpBaseFig(), 1);
@ -2416,7 +2416,7 @@ BigDecimal_power(int argc, VALUE*argv, VALUE self)
if (NIL_P(prec)) {
n += DBLE_FIG;
}
exp = GetVpValueWithPrec(vexp, DBLE_FIG, 1);
exp = GetVpValueWithPrec(vexp, 0, 1);
break;
case T_RATIONAL:
@ -2829,7 +2829,8 @@ rb_float_convert_to_BigDecimal(VALUE val, size_t digs, int raise_exception)
char buf[DBLE_FIG + BASE_FIG + 2 + 1];
int decpt, negative_p;
char *e;
char *p = BigDecimal_dtoa(d, 2, digs, &decpt, &negative_p, &e);
const int mode = digs == 0 ? 0 : 2;
char *p = BigDecimal_dtoa(d, mode, digs, &decpt, &negative_p, &e);
int len10 = (int)(e - p);
if (len10 >= (int)sizeof(buf))
len10 = (int)sizeof(buf) - 1;
@ -3006,6 +3007,7 @@ rb_convert_to_BigDecimal(VALUE val, size_t digs, int raise_exception)
VALUE copy = TypedData_Wrap_Struct(rb_cBigDecimal, &BigDecimal_data_type, 0);
vp = VpCopy(NULL, vp);
/* TODO: rounding */
BigDecimal_wrap_struct(copy, vp);
return VpCheckGetValue(vp);
}
@ -3046,19 +3048,28 @@ rb_convert_to_BigDecimal(VALUE val, size_t digs, int raise_exception)
}
/* call-seq:
* BigDecimal(initial, digits=0, exception: true)
* BigDecimal(arg, exception: true)
* BigDecimal(arg, digits, exception: true)
*
* Create a new BigDecimal object.
* Returns <i>arg</i> converted to a BigDecimal. Numeric types are converted
* directly. Other types except for String are first converted to String
* by <code>to_str</code>. Strings can be converted when it has appropriate
* forms of decimal numbers. Exceptions can be suppressed by passing
* <code>exception: false</code>.
*
* initial:: The initial value, as an Integer, a Float, a Rational,
* a BigDecimal, or a String.
* When <i>arg</i> is a Float and <i>digits</i> is <code>0</code>, the number
* of digits is determined by the algorithm of <code>dtoa</code> function
* written by David M. Gay. That algorithm is based on "How to Print Floating-
* Point Numbers Accurately" by Guy L. Steele, Jr. and Jon L. White [Proc. ACM
* SIGPLAN '90, pp. 112-126].
*
* If it is a String, spaces are ignored and unrecognized characters
* terminate the value.
* arg:: The value converted to a BigDecimal.
*
* digits:: The number of significant digits, as an Integer. If omitted or 0,
* the number of significant digits is determined from the initial
* value.
* If it is a String, spaces are ignored and unrecognized characters
* terminate the value.
*
* digits:: The number of significant digits, as an Integer. If omitted,
* the number of significant digits is determined from <i>arg</i>.
*
* The actual number of significant digits used in computation is
* usually larger than the specified number.
@ -3303,7 +3314,7 @@ BigMath_s_exp(VALUE klass, VALUE x, VALUE vprec)
infinite = isinf(flo);
nan = isnan(flo);
if (!infinite && !nan) {
vx = GetVpValueWithPrec(x, DBLE_FIG, 0);
vx = GetVpValueWithPrec(x, 0, 0);
}
break;
@ -3456,7 +3467,7 @@ get_vp_value:
infinite = isinf(flo);
nan = isnan(flo);
if (!zero && !negative && !infinite && !nan) {
vx = GetVpValueWithPrec(x, DBLE_FIG, 1);
vx = GetVpValueWithPrec(x, 0, 1);
}
break;

2
ext/bigdecimal/lib/bigdecimal/util.rb
View File

@ -43,7 +43,7 @@ class Float < Numeric
#
# See also BigDecimal::new.
#
def to_d(precision=Float::DIG+1)
def to_d(precision=0)
BigDecimal(self, precision)
end
end

2
test/bigdecimal/test_bigdecimal.rb
View File

@ -917,6 +917,7 @@ class TestBigDecimal < Test::Unit::TestCase
def test_mult_with_float
assert_kind_of(BigDecimal, BigDecimal("3") * 1.5)
assert_equal(BigDecimal("64.4"), BigDecimal(1) * 64.4)
end
def test_mult_with_rational
@ -955,6 +956,7 @@ class TestBigDecimal < Test::Unit::TestCase
def test_div_with_float
assert_kind_of(BigDecimal, BigDecimal("3") / 1.5)
assert_equal(BigDecimal("0.5"), BigDecimal(1) / 2.0)
end
def test_div_with_rational

8
test/bigdecimal/test_bigdecimal_util.rb
View File

@ -19,11 +19,11 @@ class TestBigDecimalUtil < Test::Unit::TestCase
def test_Float_to_d_without_precision
delta = 1.0/10**(Float::DIG+1)
assert_in_delta(BigDecimal(0.5, Float::DIG+1), 0.5.to_d, delta)
assert_in_delta(BigDecimal(355.0/113.0, Float::DIG+1), (355.0/113.0).to_d, delta)
assert_in_delta(BigDecimal(0.5, 0), 0.5.to_d, delta)
assert_in_delta(BigDecimal(355.0/113.0, 0), (355.0/113.0).to_d, delta)
assert_equal(9.05, 9.05.to_d.to_f)
assert_equal("9.050000000000001", 9.05.to_d.to_s('F'))
assert_equal("9.05", 9.05.to_d.to_s('F'))
assert_equal(Math::PI, Math::PI.to_d.to_f)
@ -34,6 +34,8 @@ class TestBigDecimalUtil < Test::Unit::TestCase
assert_raise(TypeError) { 0.3.to_d(false) }
assert(1.1.to_d.frozen?)
assert_equal(BigDecimal("999_999.9999"), 999_999.9999.to_d)
end
def test_Float_to_d_with_precision