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dload

retrieve double from local variable

Jasmin Syntax

     dload <varnum> or     wide     dload <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

Before	After
...	result-word1
	result-word2
	...

Description

dload retrieves a double-precision floating point number held in local variable and pushes it onto the operand stack.

Since double-precision floats are 64-bits wide, and each local variable only holds up to 32 bits, Java uses two consecutive local variables, <varnum> and <varnum> + 1 to store a double. So dload <varnum> actually places the values of both <varnum> and <varnum> + 1 onto the operand stack.

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

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 non-double value in <varnum>, then <varnum> + 1 becomes invalidated until a new value is stored in it.

Example

 dload 2         ; push the double held in local variables 2 and 3 onto the stack 

Bytecode

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

Type	Description
u1	dload opcode = 0x18 (24)
u1	<varnum>

There is also a wide format for this instruction, which supports access to all local variables from 0 to 65535:

Type	Description
u1	wide opcode = 0xC4 (196)
u1	dload opcode = 0x18 (24)
u2	<varnum>

See Also

fload, iload, aload, lload, wide

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