2 ms·

You’re probably using some exotic compiler. Most C compilers already do something very similar, check this out: https://godbolt.org/g/weicFj https://godbolt.or

You’re probably using some exotic compiler. Most C compilers already do something very similar, check this out: https://godbolt.org/g/weicFj https://godbolt.org/g/weicFj Obviously, "x / 10" is much easier to read and support, compared to these manual optimizations.

phkahler 9y ago
I'm not doing mod 10 operations, I'm printing left to right. I also put each digit in a case: and the digit printing is part of a larger state machine transmitting various things. No characters are stored, one of these blocks was run whenever the UART was ready to receive a new character. I didn't want to do the entire conversion to string all at once and this is a very fast way to extract digits in order.
- Const-me 9y ago
  Your “d = ((uint32_t)n * 53687 + 8208) >> 29;” is no faster than “d = n / 10000;” Modern compilers already apply these multiply-shift tricks when dividing by a constant.
  - phkahler 9y ago
    I was writing for an ARM based micro controller. The compiler may well have been GCC. I should have timed it vs the obvious use of division. I was not aware that they would do such things for division by arbitrary large numbers. If that's all so, then why is TFA worried about the speed of itoa?
    - Const-me 9y ago
      > I was not aware that they would do such things for division by arbitrary large numbers. They don’t, just 10000 is not large enough :-) But yeah, apparently 32-bit 10k division works on GCC ARM as well: https://godbolt.org/g/ebJqrw https://godbolt.org/g/ebJqrw > why is TFA worried about the speed of itoa? Because itoa is slow. I once needed to read / write large (100MB+) G-code files. Profiler showed me it spent majority of time in standard library routines like itoa / atof / etc. Replacing itoa with http://fmtlib.net http://fmtlib.net lead to much faster code.

2 ms·

You’re probably using some exotic compiler. Most C compilers already do something very similar, check this out: https://godbolt.org/g/weicFj https://godbolt.or

by Const-me 9y ago

phkahler 9y ago
I'm not doing mod 10 operations, I'm printing left to right. I also put each digit in a case: and the digit printing is part of a larger state machine transmitting various things. No characters are stored, one of these blocks was run whenever the UART was ready to receive a new character. I didn't want to do the entire conversion to string all at once and this is a very fast way to extract digits in order.
- Const-me 9y ago
  Your “d = ((uint32_t)n * 53687 + 8208) >> 29;” is no faster than “d = n / 10000;” Modern compilers already apply these multiply-shift tricks when dividing by a constant.
  - phkahler 9y ago
    I was writing for an ARM based micro controller. The compiler may well have been GCC. I should have timed it vs the obvious use of division. I was not aware that they would do such things for division by arbitrary large numbers. If that's all so, then why is TFA worried about the speed of itoa?
    - Const-me 9y ago
      > I was not aware that they would do such things for division by arbitrary large numbers. They don’t, just 10000 is not large enough :-) But yeah, apparently 32-bit 10k division works on GCC ARM as well: https://godbolt.org/g/ebJqrw https://godbolt.org/g/ebJqrw > why is TFA worried about the speed of itoa? Because itoa is slow. I once needed to read / write large (100MB+) G-code files. Profiler showed me it spent majority of time in standard library routines like itoa / atof / etc. Replacing itoa with http://fmtlib.net http://fmtlib.net lead to much faster code.