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lincomatic / open_evse

Firmware for Open EVSE
GNU General Public License v3.0
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Improved square root #47

Closed wmcbrine closed 8 years ago

wmcbrine commented 8 years ago

Tested (under x86) to give the same output with inputs up to 1000000, where it ran as much as 100 times faster -- yet (on Arduino) it even uses less compiled code. Taken from: https://en.wikipedia.org/wiki/Methods_of_computing_square_roots

Also includes a small patch to save 12 more bytes (206 total).

lincomatic commented 8 years ago

Thank you!

lincomatic commented 8 years ago

I turned on warnings on avr-gcc, and got this warning:

C:\Users\Geek\AppData\Local\Temp\build1349657233616483660.tmp\J1772EvseController.cpp: In function 'long unsigned int ulong_sqrt(long unsigned int)': C:\Users\Geek\AppData\Local\Temp\build1349657233616483660.tmp\J1772EvseController.cpp:35:28: warning: left shift count >= width of type [enabled by default] unsigned long bit = 1 << 30;

the line should be

unsigned long bit = 1ul << 30;

but inexplicably changing 1 to 1ul adds 256 bytes of code!!!

so does

unsigned long bit = 0x40000000ul;