Fixed associativity in units parsing.

Fixes #776

Fixed associativity in units parsing.
Fixes #776
f6f16d28 · Luc Maisonobe · cc4ef9ea · f6f16d28 · f6f16d28 · f6f16d28
Commit f6f16d28 authored Apr 06, 2021 by Luc Maisonobe
3 changed files
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -21,6 +21,9 @@
  </properties>
  <body>
    <release version="11.0" date="TBD" description="TBD">
+      <action dev="luc" type="fix" issue="776">
+        Fixed associativity in units parsing.
+      </action>
      <action dev="bryan" type="update" issue="774">
        TimeStampedFieldPVCoordinates now implements FieldTimeStamped.
      </action>

--- a/src/main/java/org/orekit/utils/units/Parser.java
+++ b/src/main/java/org/orekit/utils/units/Parser.java
@@ -26,14 +26,13 @@ import org.hipparchus.fraction.Fraction;
 * The special case "n/a" corresponds to {@link PredefinedUnit#NONE}.
 * </p>
 * <pre>
- *   unit         → "n/a"        | chain
- *   chain        → operand operation
- *   operand      → '√' simple   | simple power
- *   operation    → '*' chain    | '/' chain    | ε
- *   power        → '^' exponent | ε
- *   exponent     → integer      | '(' integer denominator ')'
- *   denominator  → '/' integer  | ε
- *   simple       → predefined   | '(' chain ')'
+ *   unit         ::=  "n/a"        | chain
+ *   chain        ::=  operand { ('*' | '/') operand }
+ *   operand      ::=  '√' simple   | simple power
+ *   power        ::=  '^' exponent | ε
+ *   exponent     ::=  integer      | '(' integer denominator ')'
+ *   denominator  ::=  '/' integer  | ε
+ *   simple       ::=  predefined   | '(' chain ')'
 * </pre>
 * <p>
 * This parses correctly units like MHz, km/√d, kg.m.s⁻¹, µas^(2/5)/(h**(2)×m)³, km/√(kg.s), √kg*km** (3/2) /(µs^2*Ω⁻⁷).
@@ -73,7 +72,18 @@ class Parser {
     * @return chain unit
     */
    private static Unit chain(final Lexer lexer) {
-        return operation(operand(lexer), lexer);
+        Unit chain = operand(lexer);
+        for (Token token = lexer.next(); token != null; token = lexer.next()) {
+            if (checkType(token, TokenType.MULTIPLICATION)) {
+                chain = chain.multiply(null, operand(lexer));
+            } else if (checkType(token, TokenType.DIVISION)) {
+                chain = chain.divide(null, operand(lexer));
+            } else {
+                lexer.pushBack();
+                break;
+            }
+        }
+        return chain;
    }

    /** Parse an operand.
@@ -93,23 +103,6 @@ class Parser {
        }
    }

-    /** Parse an operation.
-     * @param lhs left hand side unit
-     * @param lexer lexer providing tokens
-     * @return simple unit
-     */
-    private static Unit operation(final Unit lhs, final Lexer lexer) {
-        final Token token = lexer.next();
-        if (checkType(token, TokenType.MULTIPLICATION)) {
-            return lhs.multiply(null, chain(lexer));
-        } else if (checkType(token, TokenType.DIVISION)) {
-            return lhs.divide(null, chain(lexer));
-        } else {
-            lexer.pushBack();
-            return lhs;
-        }
-    }
-
    /** Parse a power operation.
     * @param lexer lexer providing tokens
     * @return exponent

--- a/src/test/java/org/orekit/utils/units/ParserTest.java
+++ b/src/test/java/org/orekit/utils/units/ParserTest.java
@@ -79,6 +79,19 @@ public class ParserTest {
                       new Fraction(-1, 2), Fraction.ONE, new Fraction(-1, 2), Fraction.ZERO);
    }

+    @Test
+    public void testLeftAssociativity() {
+        checkReference("(kg/m)/s²",
+                       1.0,
+                       Fraction.ONE, Fraction.MINUS_ONE, new Fraction(-2), Fraction.ZERO);
+        checkReference("kg/(m/s²)",
+                       1.0,
+                       Fraction.ONE, Fraction.MINUS_ONE, Fraction.TWO, Fraction.ZERO);
+        checkReference("kg/m/s²",
+                       1.0,
+                       Fraction.ONE, Fraction.MINUS_ONE, new Fraction(-2), Fraction.ZERO);
+    }
+
    @Test
    public void testEmpty() {
        expectFailure("");