[sensors] [mac] Implement ambient light sensor for macOS

device/generic_sensor/ambient_light_mac.cc

Index: device/generic_sensor/ambient_light_mac.cc
diff --git a/content/browser/device_sensors/ambient_light_mac.cc b/device/generic_sensor/ambient_light_mac.cc
similarity index 74%
rename from content/browser/device_sensors/ambient_light_mac.cc
rename to device/generic_sensor/ambient_light_mac.cc
index c6606791bd35ef399d186bc46e84c336f61f51a4..68bc459ec9c7da69f684bb0c5b373acd9b5f8882 100644
--- a/content/browser/device_sensors/ambient_light_mac.cc
+++ b/device/generic_sensor/ambient_light_mac.cc
@@ -4,14 +4,14 @@
 
 // This file is based on http://osxbook.com/book/bonus/chapter10/light/
 
-#include "content/browser/device_sensors/ambient_light_mac.h"
+#include "device/generic_sensor/ambient_light_mac.h"
 
 #include <utility>
 
 #include "base/mac/scoped_cftyperef.h"
 #include "base/mac/scoped_ioobject.h"
 
-namespace content {
+namespace device {
 
 namespace {
 enum LmuFunctionIndex {
@@ -28,13 +28,33 @@ std::unique_ptr<AmbientLightSensor> AmbientLightSensor::Create() {
   return light_sensor->Init() ? std::move(light_sensor) : nullptr;
 }
 
+double AmbientLightSensor::LMUvalueToLux(uint64_t raw_value) {
+  // Conversion formula from regression.
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=793728
+  // Let x = raw_value, then
+  // lux = -2.978303814*(10^-27)*x^4 + 2.635687683*(10^-19)*x^3 -
+  //       3.459747434*(10^-12)*x^2 + 3.905829689*(10^-5)*x - 0.1932594532
+
+  static const long double k4 = pow(10.L, -7);
+  static const long double k3 = pow(10.L, -4);
+  static const long double k2 = pow(10.L, -2);
+  static const long double k1 = pow(10.L, 5);
+  long double scaled_value = raw_value / k1;
+
+  long double lux_value =
+      (-3 * k4 * pow(scaled_value, 4)) + (2.6 * k3 * pow(scaled_value, 3)) +
+      (-3.4 * k2 * pow(scaled_value, 2)) + (3.9 * scaled_value) - 0.19;
+
+  double lux = ceil(static_cast<double>(lux_value));
+  return lux > 0 ? lux : 0;
+}
+
 AmbientLightSensor::~AmbientLightSensor() {
   if (!io_connection_)
     IOServiceClose(io_connection_);
 }
 
-AmbientLightSensor::AmbientLightSensor() : io_connection_(IO_OBJECT_NULL) {
-}
+AmbientLightSensor::AmbientLightSensor() : io_connection_(IO_OBJECT_NULL) {}
 
 bool AmbientLightSensor::Init() {
   // Tested and verified by riju that the following call works on
@@ -77,4 +97,4 @@ bool AmbientLightSensor::ReadSensorValue(uint64_t lux_values[2]) {
   return kr == KERN_SUCCESS;
 }
 
-}  // namespace content
+}  // namespace device