Flashlight using AA and 14500 batteries

I've built a number of LED lights myself.  But you can purchase a 1000LM Cree Q5 LED flashlight for less than $2.  What I found intriguing is that the flashlight is capable of running on both a regular alkaline AA battery or 14500 lithium ion battery. The AA battery voltage range is 0.9 to 1.5V, and the Li+ battery is 2.5 to 4.2V.  And the white LED forward voltage is about around 3.3 to 3.7V.  So the regulator has to be capable of both stepping up and down.  While there are circuits that can do that, I'm curious how it is done on an inexpensive flashlight.

I was able to find pictures of retail circuit boards for LED, like this one

A search for the driver IC turns up Nanjing Micro One Electronic ME2106.  The packaging is SOT-89-5 with an extended pad for VOUT, which enhances the thermal performance.  The typical application circuit looks like this,

However, ME2106 is a step-up converter with constant current output.  The IC is capable of starting at 0.8V.    The current is set by an external resistor with 200mV feedback voltage.  So the current sensing resistor appears to be 0.27 Ohm, which sets the current to 740mA.  The CREE Q5 LED is spec'ed with 3.3V@350mA, 3.5V@700mA, and 3.7V@1000mA.  The Q5 is cool white with min flux of 107 lm, increasing to 180 lm @700mA and 240 lm @1000mA.  So the advertised 1000 lm is probably bogus.  Since ME2106 is not capably of stepping down.  When the battery voltage exceeding 3.5V, the battery voltage applies to the inductor, the diode, the LED and the resistor in series.  The drop across the diode is over 0.4V and may be another 0.2V across the resistor and inductor; there is enough drop to bring the voltage across the LED down to 3.6V from the 4.2V peak battery voltage.  The efficiency is still over 80%.