Add Math.log() operator (#320)

I had a need for Math.log in an Animation calculation. This code all seemed to work and I think I found all the touch points, but I'm not well versed on the native side of things so please let me know if anything needs to change.

README.md

@@ -416,6 +416,15 @@ sqrt(nodeOrNumber)
 
 The square root of the given node. If the number is negative, an error is thrown.
 
+---
+### `log`
+
+```js
+log(nodeOrNumber)
+```
+
+The log of the given node.
+
 ---
 ### `sin`
 

android/src/main/java/com/swmansion/reanimated/nodes/OperatorNode.java

@@ -89,6 +89,12 @@ public double eval(Double x) {
       return Math.sqrt(x);
     }
   };
+  private static final Operator LOG = new SingleOperator() {
+    @Override
+    public double eval(Double x) {
+      return Math.log(x);
+    }
+  };
   private static final Operator SIN = new SingleOperator() {
     @Override
     public double eval(Double x) {
@@ -235,6 +241,8 @@ public OperatorNode(int nodeID, ReadableMap config, NodesManager nodesManager) {
       mOperator = MODULO;
     } else if ("sqrt".equals(op)) {
       mOperator = SQRT;
+    } else if ("log".equals(op)) {
+      mOperator = LOG;
     } else if ("sin".equals(op)) {
       mOperator = SIN;
     } else if ("cos".equals(op)) {

ios/Nodes/REAOperatorNode.m

@@ -45,6 +45,7 @@ - (instancetype)initWithID:(REANodeID)nodeID config:(NSDictionary<NSString *,id>
             @"pow": REA_REDUCE(pow(a, b)),
             @"modulo": REA_REDUCE(fmodf(fmodf(a, b) + b, b)),
             @"sqrt": REA_SINGLE(sqrt(a)),
+            @"log": REA_SINGLE(log(a)),
             @"sin": REA_SINGLE(sin(a)),
             @"cos": REA_SINGLE(cos(a)),
             @"tan": REA_SINGLE(tan(a)),

mock.js

@@ -52,6 +52,7 @@ module.exports = {
     pow: NOOP,
     modulo: NOOP,
     sqrt: NOOP,
+    log: NOOP,
     sin: NOOP,
     cos: NOOP,
     tan: NOOP,

react-native-reanimated.d.ts

@@ -195,6 +195,7 @@ declare module 'react-native-reanimated' {
     export const pow: MultiOperator;
     export const modulo: MultiOperator;
     export const sqrt: UnaryOperator;
+    export const log: UnaryOperator;
     export const sin: UnaryOperator;
     export const cos: UnaryOperator;
     export const tan: UnaryOperator;

src/core/AnimatedOperator.js

@@ -29,6 +29,7 @@ const OPERATIONS = {
   pow: reduce((a, b) => Math.pow(a, b)),
   modulo: reduce((a, b) => ((a % b) + b) % b),
   sqrt: single(a => Math.sqrt(a)),
+  log: single(a => Math.log(a)),
   sin: single(a => Math.sin(a)),
   cos: single(a => Math.cos(a)),
   tan: single(a => Math.tan(a)),

src/operators.js

@@ -9,6 +9,7 @@ export const divide = operator('divide');
 export const pow = operator('pow');
 export const modulo = operator('modulo');
 export const sqrt = operator('sqrt');
+export const log = operator('log');
 export const sin = operator('sin');
 export const cos = operator('cos');
 export const exp = operator('exp');