# C1: RangeCheckElimination for % operator if divisor is IntConstant

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#### Details

• Enhancement
• Resolution: Fixed
• P4
• 17
• b23

#### Description

% operator follows from this rule that the result of the remainder operation can be negative only if the dividend is negative, and can be positive only if the dividend is positive. Moreover, the magnitude of the result is always less than the magnitude of the divisor(See JLS 15.17.3).

So if y is a constant integer and not equal to 0, then we can deduce the bound of remainder operation:
x % -y ==> [0, y - 1] RCE
x % y ==> [0, y - 1] RCE
-x % y ==> [-y + 1, 0]
-x % -y ==> [-y + 1, 0]

Based on above rationale, we can apply RCE for the remainder operations whose dividend is constant integer and >= 0, e.g.:

for(int i=0;i<1000;i++){
int top5 = arr[i%5]; // Apply RCE if arr is a loop invariant
....
}

#### Attachments

1. ArithmeticRemRCE.java
2 kB
Yi Yang
2. ArithmeticRemRCE.jtr
78 kB
Yi Yang

#### People

Yi Yang
Yi Yang