DefaultASCII: reorganize math

Author: gselzer

src/main/java/net/imagej/ops/image/ascii/DefaultASCII.java

@@ -117,12 +117,17 @@ public static <T extends RealType<T>> String ascii(
 			// normalized = (value - min) / (max - min)
 			tmp.set(cursor.get());
 			tmp.sub(min);
-			// NB: if a value is below min we set tmp to zero.
-			if (tmp.compareTo(zero) < 0) tmp.setZero();
-			final double normalized = tmp.getRealDouble() / span.getRealDouble();
+			tmp.div(span);
+			final double normalized = tmp.getRealDouble();
 
 			final int charLen = CHARS.length();
-			final int charIndex = (int) (charLen * normalized);
+			int charIndex = (int) (charLen * normalized);
+
+			// NB: clamp charIndex to [0, charLen) to prevent
+			// StringIndexOutOfBoundsExceptions
+			if (charIndex < 0) charIndex = 0;
+			if (charIndex >= charLen) charIndex = charLen - 1;
+
 			c[index] = CHARS.charAt(charIndex < charLen ? charIndex : charLen - 1);
 		}