Add standard log function

trinodb · Jan 25, 2019 · f6044e6 · f6044e6
1 parent d04152e
commit f6044e6
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diff --git a/presto-docs/src/main/sphinx/functions/math.rst b/presto-docs/src/main/sphinx/functions/math.rst
@@ -89,6 +89,10 @@ Mathematical Functions
 
     Returns the natural logarithm of ``x``.
 
+.. function:: log(b, x) -> double
+
+    Returns the base ``b`` logarithm of ``x``.
+
 .. function:: log2(x) -> double
 
     Returns the base 2 logarithm of ``x``.

diff --git a/presto-main/src/main/java/io/prestosql/operator/scalar/MathFunctions.java b/presto-main/src/main/java/io/prestosql/operator/scalar/MathFunctions.java
@@ -453,6 +453,14 @@ public static double ln(@SqlType(StandardTypes.DOUBLE) double num)
         return Math.log(num);
     }
 
+    @Description("logarithm to given base")
+    @ScalarFunction
+    @SqlType(StandardTypes.DOUBLE)
+    public static double log(@SqlType(StandardTypes.DOUBLE) double base, @SqlType(StandardTypes.DOUBLE) double number)
+    {
+        return Math.log(number) / Math.log(base);
+    }
+
     @Description("logarithm to base 2")
     @ScalarFunction
     @SqlType(StandardTypes.DOUBLE)

diff --git a/presto-main/src/test/java/io/prestosql/operator/scalar/TestMathFunctions.java b/presto-main/src/test/java/io/prestosql/operator/scalar/TestMathFunctions.java
@@ -473,6 +473,20 @@ public void testLog10()
         assertFunction("log10(NULL)", DOUBLE, null);
     }
 
+    @Test
+    public void testLog()
+    {
+        for (double doubleValue : DOUBLE_VALUES) {
+            for (double base : DOUBLE_VALUES) {
+                assertFunction("log(" + base + ", " + doubleValue + ")", DOUBLE, Math.log(doubleValue) / Math.log(base));
+                assertFunction("log(REAL '" + (float) base + "', REAL'" + (float) doubleValue + "')", DOUBLE, Math.log((float) doubleValue) / Math.log((float) base));
+            }
+        }
+        assertFunction("log(NULL, NULL)", DOUBLE, null);
+        assertFunction("log(5.0E0, NULL)", DOUBLE, null);
+        assertFunction("log(NULL, 5.0E0)", DOUBLE, null);
+    }
+
     @Test
     public void testMod()
     {