5 ms·

They are all in error. "(int)Math.random()" always returns 0 because Math.random() returns [0.0, 1.0) (i.e., does not include 1). Casting that return value to a

by jimm 15y ago

They are all in error. "(int)Math.random()" always returns 0 because Math.random() returns [0.0, 1.0) (i.e., does not include 1). Casting that return value to a int will always return 0.

jerfelix 15y ago
They are not in error if you are trying to get a 0. This is yet another good technique for obfuscated code.
- nbpoole 15y ago
  Indeed. Take a look at http://www.google.com/codesearch/p?hl=en#TXS-ndgbCls/trunk/junit/org/homeunix/thecave/buddi/test/model/TransactionTest.java&q=%5C(int%5C)%5Cs*Math%5C.random%5C(%5C)&sa=N&cd=20&ct=rc&l=56 http://www.google.com/codesearch/p?hl=en#TXS-ndgbCls/trunk/j... for instance: if you weren't looking for an incorrect cast, it would be very hard to notice. Two out of three casts are correct: only one is missing the parentheses.
ubernostrum 15y ago
A lot of the results I'm seeing in the search have more problems with order of operations -- so long as you multiply the random() result by a good-sized constant before you cast to int, it actually does what it's "supposed" to do.
- spullara 15y ago
  This is the point of the post. There are no examples that aren't casting Math.random() to an int before doing anything with it thus using a pretty expensive way to represent 0.
  - ubernostrum 15y ago
    The comment I was replying to was simply saying that casting the return value of Math.random() will be 0. Which is true, but is not the issue -- order of operations (for people who think the multiplication happens before the cast) is the issue.
- masklinn 15y ago
  > so long as you multiply the random() result by a good-sized constant before you cast to int, it actually does what it's "supposed" to do. Yeah but since cast binds tighter than multiplication, any code following the pattern `(int) Math.random() * a` is broken and generates 0 every single time. For the code to work, you need `(int) (Math.random() * a)`: http://www.google.com/codesearch?q=\(int\)\s*\(\s*Math\.random\(\) http://www.google.com/codesearch?q=\(int\)\s*\(\s*Math\.rand...

by jimm 15y ago

They are all in error. "(int)Math.random()" always returns 0 because Math.random() returns [0.0, 1.0) (i.e., does not include 1). Casting that return value to a int will always return 0.

jerfelix 15y ago

They are not in error if you are trying to get a 0. This is yet another good technique for obfuscated code.

nbpoole 15y ago
Indeed. Take a look at http://www.google.com/codesearch/p?hl=en#TXS-ndgbCls/trunk/junit/org/homeunix/thecave/buddi/test/model/TransactionTest.java&q=%5C(int%5C)%5Cs*Math%5C.random%5C(%5C)&sa=N&cd=20&ct=rc&l=56 http://www.google.com/codesearch/p?hl=en#TXS-ndgbCls/trunk/j... for instance: if you weren't looking for an incorrect cast, it would be very hard to notice. Two out of three casts are correct: only one is missing the parentheses.

ubernostrum 15y ago

A lot of the results I'm seeing in the search have more problems with order of operations -- so long as you multiply the random() result by a good-sized constant before you cast to int, it actually does what it's "supposed" to do.

spullara 15y ago
This is the point of the post. There are no examples that aren't casting Math.random() to an int before doing anything with it thus using a pretty expensive way to represent 0.
- ubernostrum 15y ago
  The comment I was replying to was simply saying that casting the return value of Math.random() will be 0. Which is true, but is not the issue -- order of operations (for people who think the multiplication happens before the cast) is the issue.
masklinn 15y ago
> so long as you multiply the random() result by a good-sized constant before you cast to int, it actually does what it's "supposed" to do. Yeah but since cast binds tighter than multiplication, any code following the pattern `(int) Math.random() * a` is broken and generates 0 every single time. For the code to work, you need `(int) (Math.random() * a)`: http://www.google.com/codesearch?q=\(int\)\s*\(\s*Math\.random\(\) http://www.google.com/codesearch?q=\(int\)\s*\(\s*Math\.rand...