Re: How come this returns a decimal value ... ?

[david.kahn@xxxxxxxxxxxxxxxxx]

"Gauri Kulkarni" <gauri.kulkarni@xxxxxxxxx> wrote:

>> D IntDS DS
>> D IntNum 5I 0 INZ(0)
>> D IntChar 1 Overlay(IntNum:2)
>> *
>> C MOVE X'C0' IntChar
>>
>> Now, IntNum will contain 192.
>
> But, not very well aware of OVERLAY keyword, so wondering
> how this might have returned a decimal value in 'IntNum'.
> Can anybody please help in getting this point ?

IntNum is defined as a 5-digit integer. Internally it is stored in binary
format and occupies 2 bytes of storage. The Overlay keyword tells the
compiler that IntChar is to occupy the same portion of memory as IntNum.
The 2 following the colon specifies that the first position of IntChar -
which is only one character long - occupies the same memory location as
position 2 of IntNum.

The data structure is therefore 2 bytes long, and because IntNum is
initialised to zero, and IntNum is in binary format, it initially contains
x'0000'.

IntChar occupies the 2nd byte of the data structure so moving x'C0' to it
means the data structure now contains x'00C0'.

The value of IntNum is now 192 because it is in binary format and x'00C0'
is '0000000011000000' in binary. This is 128 + 64 = 192. Note you can
calculate the decimal value directly from the hexadecimal: (4096 x 0) +
(256 x 0) + (16 x 12) + (1 x 0) = 192.

--
Dave...


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