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Since in this platform the size of type long (64 bits) is twice the size of type int (32 bits) we should perform the multiplication in terms of long and if the product is in the integer range we downcast the result to int
| Code Block | ||
|---|---|---|
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int a,b,result; |
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long temp = (long) a\* (long)b; |
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if(temp > Integer.MAX_VALUE \|\| temp < Integer.MIN_VALUE) |
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throw ArithmeticException;//overflow |
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else |
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result = (int) temp;//Value within range, safe to downcast |
Division
Although Java throws a java.lang.ArithmeticException: / by zero exception for division by zero, there is the same issue as in C\C++ when dividing the Integer.MIN_VALUE with -1. It produces Integer.MIN_VALUE unexpectedly
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Noncompliant Code Example
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| Code Block | ||
|---|---|---|
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int a,b,result |
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result = a/b; |
Compliant Code Example
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| Code Block | ||
|---|---|---|
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if(a == Integer.MIN_VALUE && b == \-1) |
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throw ArithmeticException;//May be Integer.MIN_VALUE again???? |
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else |
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result = a/b;//safe operation |
Division
For modulo operator the only problem is if we take the modulo of Integer.MIN_VALUE with -1. The result is always 0 in JAVA so we are back to the previous rule (for division)
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If we negate Integer.MIN_VALUE we get Integer.MIN_VALUE. So we explicitely check the range
| Code Block | ||
|---|---|---|
| ||
if(a == Integer.MIN_VALUE) |
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throw ArithmeticException; |
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else |
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result = --a; |
Operations Requiring Really Long Numbers
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For instance operations on long are operations on 64 bits. For example addition:
Compliant Code Example
| Code Block | ||
|---|---|---|
| ||
java.math.BigInteger big_long_max = new java.math.BigInteger(String.valueOf(Long.MAX_VALUE)); |
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System.out.println("big_long="+big_long_max); |
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big_long_max = big_long_max.add(java.math.BigInteger.valueOf(1));//same as \++big_long_max |
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System.out.println("big_long="+big_long_max); |
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These print |
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big_long=9223372036854775807 |
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big_long=9223372036854775808//exceeds the maximum range of long, no problem\! |
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java.math.BigInteger big_long_min = new java.math.BigInteger(String.valueOf(Long.MIN_VALUE)); |
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System.out.println("big_long_min="+big_long_min); |
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big_long_min = big_long_min.subtract(java.math.BigInteger.valueOf(1));//same as \--big_long_min |
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System.out.println("big_long_min="+big_long_min);//goes bellow minimum range of long, no problem\! |
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These print: |
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big_long_min=-9223372036854775808 |
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big_long_min=-9223372036854775809 |
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if(big_long < Long.MAX_VALUE && big_long > Long.MIN_VALUE)//value within range can go to the primitive type |
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long value = big_log.longValue();//get primitive type |
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else |
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//Perform error handling. We can not downcast since the value can not be represented as a long |
We longWe can always go back to the primitive types if the BigInteger of course can be represented by the type
In the example if big_long is within long range (big_long < Long.MAX_VALUE && big_long > Long.MIN_VALUE) we can use the BigInteger method longValue() to get the long value and assign it to a variable of type long
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