Preserve integer-exact representation of numbers and allow conversion of floating point values to integers

This differentiates floating point values that are within the range of
exact integer correspondence and renders them as integers rather than
using the default java toString method which formats floating point
values in E-notation when the absolute value is at least 1e6.

Author: efd6

modules/ingest-common/src/main/java/org/elasticsearch/ingest/common/ConvertProcessor.java

@@ -102,6 +102,14 @@ public Object convert(Object value) {
         STRING {
             @Override
             public Object convert(Object value) {
+                if (isExactIntegerDouble(value)) {
+                    Long l = new Long((long) ((Double) value).doubleValue());
+                    return l.toString();
+                }
+                if (isExactIntegerFloat(value)) {
+                    Long l = new Long((long) ((Float) value).floatValue());
+                    return l.toString();
+                }
                 return value.toString();
             }
         },
@@ -149,6 +157,24 @@ public static Type fromString(String processorTag, String propertyName, String t
                 );
             }
         }
+
+        private static boolean isExactIntegerFloat(Object value) {
+            final float ABS_MAX_EXACT_FLOAT = (float) 0x1p24 - 1;
+            if (!(value instanceof Float)) {
+                return false;
+            }
+            float v = ((Float) value).floatValue();
+            return v == (long) v && -ABS_MAX_EXACT_FLOAT <= v && v <= ABS_MAX_EXACT_FLOAT;
+        }
+
+        private static boolean isExactIntegerDouble(Object value) {
+            final double ABS_MAX_EXACT_DOUBLE = 0x1p53 - 1;
+            if (!(value instanceof Double)) {
+                return false;
+            }
+            double v = ((Double) value).doubleValue();
+            return v == (long) v && -ABS_MAX_EXACT_DOUBLE <= v && v <= ABS_MAX_EXACT_DOUBLE;
+        }
     }
 
     public static final String TYPE = "convert";