Typecasting int to float before division. Which casts do I really need and which can I remove and why?

Question

When dividing by ints and I want the result to be a float I can end up with something like this.

float ratio = landscape ? 
              ((float) image.getWidth()) / ((float)image.getHeight()) : 
              ((float)image.getHeight()) / ((float)image.getWidth());

However I think I don't need every cast. When diving sometimes it seems to be auto casted. What are the rules, when does this happen?

You only need to cast one of each number in division because any float/int = float. Take a look at this SO question for a better understanding https://stackoverflow.com/a/30776990/4307644 — MeetTitan, Nov 07 '18 at 11:36
Also keep in mind that a `float` cannot represent all integer values exactly. If precision matters, use `double`. — Henry, Nov 07 '18 at 11:40

score 8 · Accepted Answer · answered Nov 07 '18 at 11:36

You need to cast at least one operand per division. The other operand will be promoted automatically.

I'd personally extract local variables though, at which point it's all implicit (which is why I'd have a comment):

// Use floating point promotion to avoid integer division
float width = image.getWidth();
float height = image.getHeight();
float ratio = landscape ? width / height : height / width;

score 2 · Answer 2 · answered Nov 07 '18 at 11:36

2

For each division, you need only 1.
So it should be:

float ratio = landscape ?
              ((float)image.getWidth() / image.getHeight()) :
              ((float)image.getHeight() / image.getWidth());

answered Nov 07 '18 at 11:36

Robert Kock

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Typecasting int to float before division. Which casts do I really need and which can I remove and why?

2 Answers2