Add + and - to prefixes

This was added to be consistent with the data file spec, which was
changed for consistency with unit expressions.  It may not be a common
expression, but it's a bit weird that you can use +/- in units but not
prefixes, even though they're in the same file!

1 files changed, 16 insertions, 0 deletions

diff --git a/src/main/java/sevenUnits/unit/UnitPrefix.java b/src/main/java/sevenUnits/unit/UnitPrefix.java
index e1f7788..824f60b 100644
--- a/src/main/java/sevenUnits/unit/UnitPrefix.java
+++ b/src/main/java/sevenUnits/unit/UnitPrefix.java
@@ -158,6 +158,22 @@ public final class UnitPrefix implements Nameable {
 	}
 	
 	/**
+	 * Adds {@code other} to this prefix and returns the result.
+	 * @since 2024-03-03
+	 */
+	public UnitPrefix plus(final UnitPrefix other) {
+		return valueOf(this.getMultiplier() + other.getMultiplier());
+	}
+
+	/**
+	 * Subtracts {@code other} from this prefix and returns the result.
+	 * @since 2024-03-03
+	 */
+	public UnitPrefix minus(final UnitPrefix other) {
+		return valueOf(this.getMultiplier() - other.getMultiplier());
+	}
+
+	/**
 	 * Multiplies this prefix by {@code other}.
 	 * 
 	 * @param other prefix to multiply by