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Convert uses input precision for output precision #114

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3 changes: 3 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

## [Unreleased]

- in `Unit.convert()` (and therfore, `Qudt.convert()`), use the precision (= number of significant digits) of the input
value as the precision of the output value (notable exception: input value `1`, which is interpreted as precision 3).

## [7.0.0] - 2025-07-22

### Added
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64 changes: 38 additions & 26 deletions qudtlib-model/src/main/java/io/github/qudtlib/model/Unit.java
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package io.github.qudtlib.model;

import static io.github.qudtlib.nodedef.Builder.buildSet;
import static java.math.BigDecimal.ONE;

import io.github.qudtlib.exception.InconvertibleQuantitiesException;
import io.github.qudtlib.nodedef.Builder;
Expand Down Expand Up @@ -395,16 +396,21 @@ public BigDecimal convert(BigDecimal value, Unit toUnit, QuantityKind quantityKi
}
BigDecimal fromOffset =
ignoreOffset ? BigDecimal.ZERO : this.getConversionOffset().orElse(BigDecimal.ZERO);
BigDecimal fromMultiplier = this.getConversionMultiplier().orElse(BigDecimal.ONE);
BigDecimal fromMultiplier = this.getConversionMultiplier().orElse(ONE);
BigDecimal toOffset =
ignoreOffset
? BigDecimal.ZERO
: toUnit.getConversionOffset().orElse(BigDecimal.ZERO);
BigDecimal toMultiplier = toUnit.getConversionMultiplier().orElse(BigDecimal.ONE);
return value.add(fromOffset)
.multiply(fromMultiplier, MathContext.DECIMAL128)
.divide(toMultiplier, MathContext.DECIMAL128)
.subtract(toOffset);
BigDecimal toMultiplier = toUnit.getConversionMultiplier().orElse(ONE);
BigDecimal result =
value.add(fromOffset)
.multiply(fromMultiplier, MathContext.DECIMAL128)
.divide(toMultiplier, MathContext.DECIMAL128)
.subtract(toOffset);
int resultPrecision = Math.min(BigDecimal.ONE.equals(value) ? 3 : value.precision(), 34);

MathContext resultContext = new MathContext(resultPrecision);
return result.round(resultContext);
}

/**
Expand All @@ -417,7 +423,7 @@ public BigDecimal convert(BigDecimal value, Unit toUnit, QuantityKind quantityKi
*/
public BigDecimal getConversionMultiplier(Unit toUnit) {
if (this.equals(toUnit)) {
return BigDecimal.ONE;
return ONE;
}
if (this.conversionOffsetDiffers(toUnit)) {
throw new IllegalArgumentException(
Expand All @@ -427,25 +433,31 @@ public BigDecimal getConversionMultiplier(Unit toUnit) {
}
Optional<BigDecimal> fromMultiplier = this.getConversionMultiplier();
Optional<BigDecimal> toMultiplier = toUnit.getConversionMultiplier();
return fromMultiplier
.map(
from ->
toMultiplier
.map(to -> from.divide(to, MathContext.DECIMAL128))
.orElse(null))
.orElseThrow(
() ->
new InconvertibleQuantitiesException(
String.format(
"Cannot convert %s(%s) to %s(%s)",
this.getIriAbbreviated(),
this.getConversionMultiplier().isEmpty()
? "no multiplier"
: "has multiplier",
toUnit.getIriAbbreviated(),
toUnit.getConversionMultiplier().isEmpty()
? "no multiplier"
: "has multiplier")));
BigDecimal result =
fromMultiplier
.map(
from ->
toMultiplier
.map(to -> from.divide(to, MathContext.DECIMAL128))
.orElse(null))
.orElseThrow(
() ->
new InconvertibleQuantitiesException(
String.format(
"Cannot convert %s(%s) to %s(%s)",
this.getIriAbbreviated(),
this.getConversionMultiplier().isEmpty()
? "no multiplier"
: "has multiplier",
toUnit.getIriAbbreviated(),
toUnit.getConversionMultiplier().isEmpty()
? "no multiplier"
: "has multiplier")));
int precision = Math.min(34, result.precision());
return result.round(
new MathContext(
precision)); // TODO: when units know about their precision we can improve
// this
}

public boolean conversionOffsetDiffers(Unit other) {
Expand Down
22 changes: 11 additions & 11 deletions qudtlib-test/src/test/java/io/github/qudtlib/QudtTests.java
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Expand Up @@ -489,21 +489,19 @@ public void testInconvertible() {

@Test
public void testConvert_L_to_GAL_US() {
BigDecimal converted = Qudt.convert(BigDecimal.ONE, Qudt.Units.L, Qudt.Units.GAL_US);
MatcherAssert.assertThat(
converted,
Matchers.comparesEqualTo(new BigDecimal("0.2641720523581484153798999216091625")));
BigDecimal converted = Qudt.convert(new BigDecimal(1.00), Qudt.Units.L, Qudt.Units.GAL_US);
MatcherAssert.assertThat(converted, Matchers.comparesEqualTo(new BigDecimal("0.264")));
}

@Test
public void testConvert_Celsius_to_Fahrenheit() {
QuantityValue celsius100 =
new QuantityValue(new BigDecimal("100"), Qudt.unitFromLocalnameRequired("DEG_C"));
new QuantityValue(
new BigDecimal("100.00"), Qudt.unitFromLocalnameRequired("DEG_C"));
QuantityValue fahrenheit = Qudt.convert(celsius100, Qudt.unitIriFromLocalname("DEG_F"));
Assertions.assertNotNull(fahrenheit);
MatcherAssert.assertThat(
fahrenheit.getValue(),
Matchers.comparesEqualTo(new BigDecimal("211.9999999999999999999999999999999")));
fahrenheit.getValue(), Matchers.comparesEqualTo(new BigDecimal("212")));
Assertions.assertEquals(Qudt.unitIriFromLocalname("DEG_F"), fahrenheit.getUnit().getIri());
}

Expand Down Expand Up @@ -533,14 +531,14 @@ public void testConvert_Celsius_to_Kelvin_tempdiff() {
public void testConvert_Celsius_to_Fahrenheit_2() {
MatcherAssert.assertThat(
Qudt.convert(new BigDecimal("100"), Units.DEG_C, Units.DEG_F),
Matchers.comparesEqualTo(new BigDecimal("211.9999999999999999999999999999999")));
Matchers.comparesEqualTo(new BigDecimal("212")));
}

@Test
public void testConvert_Fahrenheit_to_Celsius() {
MatcherAssert.assertThat(
Qudt.convert(new BigDecimal("100"), Units.DEG_F, Units.DEG_C),
Matchers.comparesEqualTo(new BigDecimal("37.7777777777777777777777777777778")));
Matchers.comparesEqualTo(new BigDecimal("37.8")));
}

@Test
Expand Down Expand Up @@ -601,9 +599,11 @@ public void testConvert_FemtoGM_to_KiloGM() {
@Test
public void testConvert_Metric_to_Imperial() {
BigDecimal converted = Qudt.convert(BigDecimal.ONE, Qudt.Units.LB, Qudt.Units.KiloGM);
MatcherAssert.assertThat(converted, Matchers.comparesEqualTo(new BigDecimal("0.45359237")));
MatcherAssert.assertThat(converted, Matchers.comparesEqualTo(new BigDecimal("0.454")));
converted = Qudt.convert(new BigDecimal("1.0"), Qudt.Units.LB, Qudt.Units.KiloGM);
MatcherAssert.assertThat(converted, Matchers.comparesEqualTo(new BigDecimal("0.45")));
converted = Qudt.convert(BigDecimal.ONE, Qudt.Units.BTU_IT__PER__LB, Qudt.Units.J__PER__GM);
MatcherAssert.assertThat(converted, Matchers.comparesEqualTo(new BigDecimal("2.326")));
MatcherAssert.assertThat(converted, Matchers.comparesEqualTo(new BigDecimal("2.33")));
}

@Test
Expand Down