Java Virtual Machine (Java Series)

lstore

lstore <varnum> or wide lstore <varnum> In the first form, <varnum> is an unsigned integer in the range 0 to 0xFF. In the second (wide) form, <varnum> is an unsigned integer in the range 0 to 0xFFFE.

Stack

lstore pops a two-word long integer off the operand stack and stores it in a local variable. It takes a single parameter, <varnum>, an unsigned integer indicating which local variable to use.

Since long integers are 64-bits wide, and each local variable can only hold up to 32 bits Java uses two consecutive local variables, <varnum> and <varnum> + 1 to store a long. So lstore <varnum> actually modifies the values of both <varnum> (which is set to long-word1) and <varnum> + 1 (which is set to long-word2).

Both <varnum> and <varnum> + 1 must be valid local variable numbers in the current frame, and together they must be holding a long.

Remember that attempting to treat two-word values as two independent single-word values will produce a verification error. So trying to retrieve <varnum> or <varnum> + 1 independently (e.g. iload <varnum>) will produce a verification error. Similarly, if you store a value other than a long in <varnum>, then <varnum> + 1 becomes invalidated until a new value is stored in it.

Example

ldc2_w 10 ; push the long integer 10 onto the stack lstore 3 ; pop 10 off of the stack and store it in local variables 3 and 4 Bytecode

For local variable numbers in the range 0-255, use:

istore, fstore, dstore, astore, wide

Java Virtual Machine, by Jon Meyer and Troy Downing, O'Reilly Associates