From 798bcbee01467ac48347d54405277104ccdedec5 Mon Sep 17 00:00:00 2001
From: Fabian Guerra <fabian.guerra@mapbox.com>
Date: Tue, 17 Apr 2018 17:14:42 -0400
Subject: [ios, macos] Add log2 NSExpresssion operator.

---
 platform/darwin/src/NSExpression+MGLAdditions.mm | 10 ++++++++++
 platform/darwin/test/MGLExpressionTests.mm       |  7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index e641c79628..46a463430b 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -74,6 +74,7 @@ const MGLExpressionInterpolationMode MGLExpressionInterpolationModeCubicBezier =
     INSTALL_METHOD(mgl_sin:);
     INSTALL_METHOD(mgl_atan:);
     INSTALL_METHOD(mgl_tan:);
+    INSTALL_METHOD(mgl_log2:);
     
     // Install functions that resemble control structures, taking arbitrary
     // numbers of arguments. Vararg aftermarket functions need to be declared
@@ -145,6 +146,13 @@ const MGLExpressionInterpolationMode MGLExpressionInterpolationModeCubicBezier =
     return @(tan(number.doubleValue));
 }
 
+/**
+ Computes the logarithm base two of the value.
+ */
+- (NSNumber *)mgl_log2:(NSNumber *)number {
+    return @(log2(number.doubleValue));
+}
+
 /**
  A placeholder for a method that evaluates an interpolation expression.
  */
@@ -729,6 +737,7 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             @"sin" : @"mgl_sin:",
             @"atan" : @"mgl_atan:",
             @"tan" : @"mgl_tan:",
+            @"log2" : @"mgl_log2:",
             @"floor": @"floor:",
             @"ceil": @"ceiling:",
             @"^": @"raise:toPower:",
@@ -977,6 +986,7 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             @"mgl_sin:" : @"sin",
             @"mgl_atan:" : @"atan",
             @"mgl_tan:" : @"tan",
+            @"mgl_log2:" : @"log2",
             // Vararg aftermarket expressions need to be declared with an explicit and implicit first argument.
             @"MGL_LET": @"let",
             @"MGL_LET:": @"let",
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index 864310356c..d7c86ed07c 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -503,6 +503,13 @@ using namespace std::string_literals;
         XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
         XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
     }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"mgl_log2:" arguments:@[MGLConstantExpression(@1024)]];
+        NSArray *jsonExpression = @[@"log2", @1024];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @10);
+        XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
+    }
     {
         NSExpression *expression = [NSExpression expressionForFunction:@"raise:toPower:" arguments:arguments];
         NSArray *jsonExpression = @[@"^", @1, @1];
-- 
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