Why is 15 the max?

[BlinkyStitt]

With --zeros, I'm finding 15 really fast. Why is the max currently bound between 0 and 15 (f)?

./ERADICATE2.x64 -A 0x00000000000000000000000000000000deadbeef -I 0x00 --zeros
Devices:
  GPU0: Intel(R) Gen9 HD Graphics NEO, 26831261696 bytes available, 48 compute units

Initializing OpenCL...
  Creating context...OK
  Compiling kernel...OK
  Building program...OK

Running...

  Time:     1s Score: 14 Salt: 0xcd6ec5f93e88d1d34cb058f487ae3817e455667b9544d9e68c6408d3d89c39c2 Address: 0x7f7ba907683006c4010900093002e00eb503af0c
  Time:     1s Score: 15 Salt: 0xcd6ec5f93e88d17b9e3859f587ae3817e455667b9544d9e68c6408d3d89c39c2 Address: 0x0ed0700bcd0f0704b77480b20240c603030a00e8
Speed: 24.067 MH/s GPU0: 24.067 MH/s

[BlinkyStitt]

I think range is not doing what I expected.