Another take on decimal data types
kdevel
kdevel at vogtner.de
Sat Jan 13 18:37:10 UTC 2018
On Saturday, 13 January 2018 at 17:46:15 UTC, rumbu wrote:
> The following code works:
>
> real r;
> for (r = 1; r < 6; r += .1L) {
> decimal128 d = r;
> auto dsin = sin (d);
> auto rsin = sin (r);
> auto delta = dsin - rsin; //delta is decimal128
> writefln ("%9.2f %30.24f %30.24f %12.4g", r, rsin,
> dsin, delta);
> }
rsinus.d
```
import std.stdio;
import std.math;
import decimal;
void main ()
{
real r;
for (r = 1; r < 6; r += .1L) {
decimal128 d = r;
auto dsin = sin (d);
auto rsin = sin (r);
auto delta = dsin - rsin;
writefln ("%9.2f %30.24f %30.24f %12.4g", r, rsin, dsin,
delta);
}
}
```
I get large numerical dicrepancies and an exception:
1.00 0.841470984807896506664591
0.841470984807896506632968 3.633e-18
1.10 0.891207360061435339970703
0.878166666666666700439167 -1e-02
1.20 0.932039085967226349689098
0.932735999999999982229600 1e-04
1.30 0.963558185417192964729825
0.964774416666666678037840 1e-03
1.40 0.985449729988460180693261
0.985449729988460165022208 2.352e-17
1.50 0.997494986604054430972058
0.997494986604054430940101 -1.206e-17
1.60 0.999573603041505164359688
0.917333333333333309393333 -1e-02
1.70 0.991664810452468615338453
0.991664810452468621659666 5.316e-17
1.80 0.973847630878195186514452
0.973847630878195177217801 3.222e-17
1.90 0.946300087687414488452770
0.946300087687414518558711 5.006e-17
2.00 0.909297426825681695322298
0.909297426825681695408286 -1.229e-17
2.10 0.863209366648873770600393
0.863209366648873727768592 -9.243e-17
2.20 0.808496403819590184279108
0.808496403819590083669388 -1.180e-16
2.30 0.745705212176720177432929
0.745705212176720299976718 1.573e-16
2.40 0.675463180551150926659871
0.675463180551150998081025 4.488e-17
2.50 0.598472144103956494242628
0.598472144103956494052117 -5.365e-17
2.60 0.515501371821464235509908
0.515501371821464164136844 -1.059e-16
2.70 0.427379880233829934906920
0.427379880233829779962563 -1.640e-16
2.80 0.334988150155904919986691
0.334988150155905092912699 1.534e-16
2.90 0.239249329213982328722001
0.239249329213982423337949 8.154e-17
3.00 0.141120008059867222739193
0.141120008059867222100109 9.000e-18
3.10 0.041580662433290579926783
0.041580662433290496264607 -8.502e-17
3.20 -0.058374143427579908318645
-0.058374143427580079845578 -1.746e-16
3.30 -0.157745694143248381115198
-0.157745694143248199327762 1.774e-16
3.40 -0.255541102026831318288136
-0.255541102026831224503296 1.098e-16
3.50 -0.350783227689619847116916
-0.350783227689619848119312 -1.252e-17
3.60 -0.442520443294852383234834
-0.442520443294852457798085 -5.310e-17
3.70 -0.529836140908493212172466
-0.529836140908493358228498 -1.787e-16
3.80 -0.611857890942719074699619
-0.611857890942718929385788 9.811e-17
3.90 -0.687766159183973817053612
-0.687766159183973746224122 2.078e-17
4.00 -0.756802495307928250372134
-0.756802495307928251373997 -5.067e-17
4.10 -0.818277111064410503490831
-0.818277111064410297331800 1.797e-16
4.20 -0.871575772413588059281658
-0.871575772413588143861425 -6.686e-17
4.30 -0.916165936749454983402223
-0.916165936749454908701153 1.013e-16
4.40 -0.951602073889515953533484
-0.951602073889516059449964 -1.634e-16
4.50 -0.977530117665097055001684
-0.977530117665097055387688 -4.889e-17
4.60 -0.993691003633464455912887
-0.993691003633464414974720 -8.475e-18
4.70 -0.999923257564100884174467
-0.999923257564100886240565 -5.624e-17
4.80 -0.996164608835840671935500
-0.996164608835840688651004 -8.651e-18
4.90 -0.982452612624332512691275
-0.982452612624332448489733 2.651e-17
5.00 -0.958924274663138469525139
-0.958924274663138468894495 -1.739e-17
5.10 -0.925814682327732297803524
-0.925814682327732436044974 -9.704e-17
5.20 -0.883454655720153265790421
-0.883454655720153186437488 5.926e-17
5.30 -0.832267442223901164892897
-0.832267442223901270573400 -1.281e-16
5.40 -0.772764487555987363974919
-0.772764487555987145324893 2.202e-16
5.50 -0.705540325570391908089566
-0.705540325570391906230803 1.647e-17
5.60 -0.631266637872321313522395
-0.631266637872321596869491 -3.079e-16
5.70 -0.550685542597637763537807
-25.165500000000002545915000 -
core.exception.RangeError at decimal/package.d(6652): Range violation
----------------
??:? _d_arrayboundsp [0x46ccea]
decimal/package.d:6652 void decimal.sinkFloat!(char,
decimal.integrals.unsigned!(128).unsigned).sinkFloat(ref
const(std.format.FormatSpec!(char).FormatSpec), void
delegate(const(char)[]),
const(decimal.integrals.unsigned!(128).unsigned), const(int),
const(bool), const(decimal.RoundingMode), const(bool)) [0x460a41]
decimal/package.d:6851 void decimal.sinkGeneral!(char,
decimal.integrals.unsigned!(128).unsigned).sinkGeneral(ref
const(std.format.FormatSpec!(char).FormatSpec), void
delegate(const(char)[]),
const(decimal.integrals.unsigned!(128).unsigned), const(int),
const(bool), const(decimal.RoundingMode)) [0x461ae9]
decimal/package.d:6890 void decimal.sinkDecimal!(char,
decimal.Decimal!(128).Decimal).sinkDecimal(ref
const(std.format.FormatSpec!(char).FormatSpec), void
delegate(const(char)[]), ref
const(decimal.Decimal!(128).Decimal),
const(decimal.RoundingMode)) [0x460208]
decimal/package.d:1316 const void
decimal.Decimal!(128).Decimal.toString!(char).toString(scope void
delegate(const(char)[]), std.format.FormatSpec!(char).FormatSpec)
[0x45fff1]
/.../dmd2/linux/bin64/../../src/phobos/std/format.d:3341 void
std.format.formatObject!(std.stdio.File.LockingTextWriter,
decimal.Decimal!(128).Decimal, char).formatObject(ref
std.stdio.File.LockingTextWriter, ref
decimal.Decimal!(128).Decimal, ref
const(std.format.FormatSpec!(char).FormatSpec)) [0x4620c2]
/.../dmd2/linux/bin64/../../src/phobos/std/format.d:3669 void
std.format.formatValue!(std.stdio.File.LockingTextWriter,
decimal.Decimal!(128).Decimal, char).formatValue(ref
std.stdio.File.LockingTextWriter, ref
decimal.Decimal!(128).Decimal, ref
const(std.format.FormatSpec!(char).FormatSpec)) [0x462069]
/.../dmd2/linux/bin64/../../src/phobos/std/format.d:568 uint
std.format.formattedWrite!(std.stdio.File.LockingTextWriter,
char, real, real, decimal.Decimal!(128).Decimal,
decimal.Decimal!(128).Decimal).formattedWrite(ref
std.stdio.File.LockingTextWriter, const(char[]), real, real,
decimal.Decimal!(128).Decimal, decimal.Decimal!(128).Decimal)
[0x45711b]
/.../dmd2/linux/bin64/../../src/phobos/std/stdio.d:1496 void
std.stdio.File.writefln!(char, real, real,
decimal.Decimal!(128).Decimal,
decimal.Decimal!(128).Decimal).writefln(const(char[]), real,
real, decimal.Decimal!(128).Decimal,
decimal.Decimal!(128).Decimal) [0x456be6]
/.../dmd2/linux/bin64/../../src/phobos/std/stdio.d:3797 void
std.stdio.writefln!(char, real, real,
decimal.Decimal!(128).Decimal,
decimal.Decimal!(128).Decimal).writefln(const(char[]), real,
real, decimal.Decimal!(128).Decimal,
decimal.Decimal!(128).Decimal) [0x456b37]
rsinus.d:12 _Dmain [0x44c27d]
> if you really need to convert decimalX values to floating point
> counterparts, you'll need to cast them:
>
> x = cast(real)somedecimalvalue;
>
> (but update your files before this, I discovered a bug in
> opCast)
Yea, this seems to work now.
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