Faster division by 1000

release-notes/CREDITS-2.x

@@ -426,3 +426,7 @@ Guillaume Lecroc (@gulecroc)
  * Contributed #1179: Allow configuring `DefaultPrettyPrinter` separators for empty
    Arrays and Objects
   (2.17.0)
+
+Antonin Janec (@xtonic)
+ * Contributed #1203: Faster division by 1000
+  (2.17.0)

release-notes/VERSION-2.x

@@ -38,6 +38,8 @@ a pure JSON library.
 #1195: Use `BufferRecycler` provided by output (`OutputStream`, `Writer`) object if available
  (contributed by Mario F)
 #1202: Add `RecyclerPool.clear()` method for dropping all pooled Objects
+#1203: Faster division by 1000
+ (contributed by @xtonik)
 #1205: JsonFactory.setStreamReadConstraints(StreamReadConstraints) fails to
   update "maxNameLength" for symbol tables
  (reported by @denizk)

src/main/java/com/fasterxml/jackson/core/io/NumberOutput.java

@@ -85,7 +85,7 @@ public static int outputInt(int v, char[] b, int off)
                 }
                 return _leading3(v, b, off);
             }
-            int thousands = v / 1000;
+            int thousands = divBy1000(v);
             v -= (thousands * 1000); // == value % 1000
             off = _leading3(thousands, b, off);
             off = _full3(v, b, off);
@@ -107,10 +107,10 @@ public static int outputInt(int v, char[] b, int off)
             }
             return _outputFullBillion(v, b, off);
         }
-        int newValue = v / 1000;
+        int newValue = divBy1000(v);
         int ones = (v - (newValue * 1000)); // == value % 1000
         v = newValue;
-        newValue /= 1000;
+        newValue = divBy1000(newValue);
         int thousands = (v - (newValue * 1000));
 
         off = _leading3(newValue, b, off);
@@ -136,7 +136,7 @@ public static int outputInt(int v, byte[] b, int off)
                     off = _leading3(v, b, off);
                 }
             } else {
-                int thousands = v / 1000;
+                int thousands = divBy1000(v);
                 v -= (thousands * 1000); // == value % 1000
                 off = _leading3(thousands, b, off);
                 off = _full3(v, b, off);
@@ -153,10 +153,10 @@ public static int outputInt(int v, byte[] b, int off)
             }
             return _outputFullBillion(v, b, off);
         }
-        int newValue = v / 1000;
+        int newValue = divBy1000(v);
         int ones = (v - (newValue * 1000)); // == value % 1000
         v = newValue;
-        newValue /= 1000;
+        newValue = divBy1000(newValue);
         int thousands = (v - (newValue * 1000));
         off = _leading3(newValue, b, off);
         off = _full3(thousands, b, off);
@@ -245,6 +245,16 @@ public static int outputLong(long v, byte[] b, int off)
         return _outputFullBillion((int) v, b, off);
     }
 
+    /**
+     * Optimized code for integer division by 1000; typically 50% higher
+     * throughput for calculation
+     *
+     * @since 2.17
+     */
+    static int divBy1000(int number) {
+        return (int) (number * 274_877_907L >>> 38);
+    }
+
     /*
     /**********************************************************
     /* Convenience serialization methods
@@ -359,13 +369,13 @@ private static int _outputUptoBillion(int v, char[] b, int off)
             if (v < 1000) {
                 return _leading3(v, b, off);
             }
-            int thousands = v / 1000;
+            int thousands = divBy1000(v);
             int ones = v - (thousands * 1000); // == value % 1000
             return _outputUptoMillion(b, off, thousands, ones);
         }
-        int thousands = v / 1000;
+        int thousands = divBy1000(v);
         int ones = (v - (thousands * 1000)); // == value % 1000
-        int millions = thousands / 1000;
+        int millions = divBy1000(thousands);
         thousands -= (millions * 1000);
 
         off = _leading3(millions, b, off);
@@ -385,9 +395,9 @@ private static int _outputUptoBillion(int v, char[] b, int off)
 
     private static int _outputFullBillion(int v, char[] b, int off)
     {
-        int thousands = v / 1000;
+        int thousands = divBy1000(v);
         int ones = (v - (thousands * 1000)); // == value % 1000
-        int millions = thousands / 1000;
+        int millions = divBy1000(thousands);
 
         int enc = TRIPLET_TO_CHARS[millions];
         b[off++] = (char) (enc >> 16);
@@ -414,13 +424,13 @@ private static int _outputUptoBillion(int v, byte[] b, int off)
             if (v < 1000) {
                 return _leading3(v, b, off);
             }
-            int thousands = v / 1000;
+            int thousands = divBy1000(v);
             int ones = v - (thousands * 1000); // == value % 1000
             return _outputUptoMillion(b, off, thousands, ones);
         }
-        int thousands = v / 1000;
+        int thousands = divBy1000(v);
         int ones = (v - (thousands * 1000)); // == value % 1000
-        int millions = thousands / 1000;
+        int millions = divBy1000(thousands);
         thousands -= (millions * 1000);
 
         off = _leading3(millions, b, off);
@@ -440,9 +450,9 @@ private static int _outputUptoBillion(int v, byte[] b, int off)
 
     private static int _outputFullBillion(int v, byte[] b, int off)
     {
-        int thousands = v / 1000;
+        int thousands = divBy1000(v);
         int ones = (v - (thousands * 1000)); // == value % 1000
-        int millions = thousands / 1000;
+        int millions = divBy1000(thousands);
         thousands -= (millions * 1000);
 
         int enc = TRIPLET_TO_CHARS[millions];

src/main/java/com/fasterxml/jackson/core/sym/ByteQuadsCanonicalizer.java

@@ -1096,13 +1096,18 @@ private int _resizeAndFindOffsetForAdd(int hash) throws StreamConstraintsExcepti
         return offset;
     }
 
+    // @since 2.17
+    static int multiplyByFourFifths(int number) {
+        return (int) (number * 3_435_973_837L >>> 32);
+    }
+
     // Helper method for checking if we should simply rehash() before add
     private boolean _checkNeedForRehash() {
         // Yes if above 80%, or above 50% AND have ~1% spill-overs
         if (_count > (_hashSize >> 1)) { // over 50%
             int spillCount = (_spilloverEnd - _spilloverStart()) >> 2;
             if ((spillCount > (1 + _count >> 7))
-                    || (_count > (_hashSize * 0.80))) {
+                    || (_count > multiplyByFourFifths(_hashSize))) {
                 return true;
             }
         }

src/test/java/com/fasterxml/jackson/core/io/NumberOutputTest.java

@@ -0,0 +1,48 @@
+package com.fasterxml.jackson.core.io;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.fail;
+
+public class NumberOutputTest
+{
+    @Test
+    public void testDivBy1000Small()
+    {
+        for (int number = 0; number <= 999_999; ++number) {
+            int expected = number / 1000;
+            int actual = NumberOutput.divBy1000(number);
+            if (expected != actual) { // only construct String if fail
+                fail("With "+number+" should get "+expected+", got: "+actual);
+            }
+        }
+    }
+
+    @Test
+    public void testDivBy1000Sampled()
+    {
+        for (int number = 1_000_000; number > 0; number += 7) {
+            int expected = number / 1000;
+            int actual = NumberOutput.divBy1000(number);
+            if (expected != actual) { // only construct String if fail
+                fail("With "+number+" should get "+expected+", got: "+actual);
+            }
+        }
+    }
+
+    // And then full range, not included in CI since code shouldn't change;
+    // but has been run to verify full range manually
+    @Test
+    // Comment out for manual testing:
+    @Disabled
+    public void testDivBy1000FullRange() {
+        for (int number = 0; number <= Integer.MAX_VALUE; ++number) {
+            int expected = number / 1000;
+            int actual = NumberOutput.divBy1000(number);
+            if (expected != actual) { // only construct String if fail
+                fail("With "+number+" should get "+expected+", got: "+actual);
+            }
+        }
+    }
+}

src/test/java/com/fasterxml/jackson/core/sym/ByteQuadsCanonicalizerTest.java

@@ -0,0 +1,19 @@
+package com.fasterxml.jackson.core.sym;
+
+import org.junit.Ignore;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class ByteQuadsCanonicalizerTest {
+    @Test
+    @Ignore
+    public void testMultiplyByFourFifths() {
+        for (long i = 0; i <= Integer.MAX_VALUE; i++) {
+            int number = (int) i;
+            int expected = (int) (number * 0.80);
+            int actual = ByteQuadsCanonicalizer.multiplyByFourFifths(number);
+            assertEquals("input=" + number, expected, actual);
+        }
+    }
+}