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Logic and integer arithmetic

A look at the bytecodes of the Java virtual machine that perform logical and arithmetic operations

By Bill Venners, JavaWorld.com, 11/11/96

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Page 3 of 5



Opcode Operand(s) Description


isub (none) pops two ints, subtracts them, and pushes the int result


lsub (none) pops two longs, subtracts them, and pushes the long result


Integer multiplication of ints and longs is accomplished via the following opcodes. Each opcode causes two values of the same type to be popped off the stack and multiplied. The result, of the same type as the numbers being multiplied, is pushed back onto the stack. No exceptions are thrown.



Opcode Operand(s) Description


imul (none) pops two ints, multiplies them, and pushes the int result


lmul (none) pops two longs, multiplies them, and pushes the long result


The opcodes that perform division on ints and longs are shown in the next table. The division opcodes cause the top two values of the appropriate type to be popped off the stack. The topmost value is divided by the value just beneath the topmost value. The result is pushed onto the stack. Integer division yields a result that is truncated down to the nearest integer value between it and zero. Integer division by zero throws a "/ by 0" ArithmeticException.



Opcode Operand(s) Description


idiv (none) pops two ints, divides them, and pushes the int result


ldiv (none) pops two longs, divides them, and pushes the long result


The remainder operation is accomplished via the following opcodes on ints and longs. The following opcodes cause the top two values to be popped from the stack. The topmost value is divided by the value just beneath it, and the remainder of that division is pushed back onto the stack. As with the division opcodes, integer remainder by zero throws a "/ by 0" ArithmeticException.



Opcode Operand(s) Description


irem (none) pops two ints, divides them, and pushes the int remainder


lrem (none) pops two longs, divides them, and pushes the long remainder


The following opcodes perform arithmetic negation on ints and longs. The negation opcodes pop the top value from the stack, negate it, and push the result.



Opcode Operand(s) Description


ineg (none) pops an int, negates it, and pushes the result


lneg (none) pops a long, negates it, and pushes the result


Logical operands

The JVM's logic capabilities operate on ints and longs. These operations treat ints and longs not as signed two's-complement numbers, necessarily, but more as generic bit patterns. Integer shifting is accomplished via the ishl, ishr, and iushr opcodes. Java's << operator is implemented by ishl. The >> operator is implemented by ishr, and the >>> operator is implemented by iushl. The difference between ishr and iushr is that only ishr does sign extension. The following table shows the instructions that shift ints left and right.



Opcode Operand(s) Description


ishl (none) shifts int left


ishr (none) arithmetic shifts int right


iushr (none) logical shifts int right


The next table shows the instructions that shift longs left and right.



Opcode Operand(s) Description


lshl (none) shifts long left


lshr (none) arithmetic shifts long right


lushr (none) logical shifts long right


The following opcodes perform bitwise logical operations on ints. The opcodes implement Java's &, |, and ^ operators.

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Resources
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