How to alter a float by its smallest increment (or close to it)?

by

Check your math.h file. If you’re lucky you have the nextafter and nextafterf functions defined. They do exactly what you want in a portable and platform independent way and are part of the C99 standard.

Another way to do it (could be a fallback solution) is to decompose your float into the mantissa and exponent part. Incrementing is easy: Just add one to the mantissa. If you get an overflow you have to handle this by incrementing your exponent. Decrementing works the same way.

EDIT: As pointed out in the comments it is sufficient to just increment the float in it’s binary representation. The mantissa-overflow will increment the exponent, and that’s exactly what we want.

That’s in a nutshell the same thing that nextafter does.

This won’t be completely portable though. You would have to deal with endianess and the fact that not all machines do have IEEE floats (ok – the last reason is more academic).

Also handling NAN’s and infinites can be a bit tricky. You cannot simply increment them as they are by definition not numbers.

More Related Contents:

  1. What is the most effective way for float and double comparison?
  2. How do I print a double value with full precision using cout?
  3. Random float number generation
  4. What is the difference between float and double?
  5. How can I write a power function myself?
  6. Sin and Cos give unexpected results for well-known angles
  7. Efficient implementation of log2(__m256d) in AVX2
  8. long double vs double
  9. Difference in floating point arithmetics between x86 and x64
  10. Why is my integer math with std::pow giving the wrong answer?
  11. Why did Microsoft abandon long double data type? [closed]
  12. How to detect double precision floating point overflow and underflow?
  13. Set back default floating point print precision in C++
  14. How computer does floating point arithmetic?
  15. Comparison of double, long double, float and float128?
  16. How to correctly and standardly compare floats?
  17. Convert a float to a string
  18. Math precision requirements of C and C++ standard
  19. Should we generally use float literals for floats instead of the simpler double literals?
  20. printf rounding behavior for doubles
  21. Why do sin(45) and cos(45) give different results? [duplicate]
  22. C++ floating point to integer type conversions
  23. Check double variable if it contains an integer, and not floating point
  24. How to write a Float Mat to a file in OpenCV
  25. Printing double without losing precision
  26. Does one double promote every int in the equation to double?
  27. Handling overflow when casting doubles to integers in C
  28. When a float variable goes out of the float limits, what happens?
  29. Extra leading zeros when printing float using printf?
  30. Does setprecision in c++ round? If so why am I seeing this?

Leave a Comment