C++ to PB help

[Tim Camarda]

Hello,

I have some C++ code that I am trying to translate to PB code:

for(i=clear_pos-1,lmask=0XFFF,dshift=12:i>+0X10:I>>=1{
lmask >>+ 1: /* bit mask for length*?
dshift__ /* shift width for delta */

is dshift a C++ built in function?



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[Michael Torrie]

No. C++ has extremely few built-in operators and functions.

Just looking at your code fragment, it appears to not be valid C++ code (missing parenthesis, braces, semicolons). Looking more closely at the code, it appears dshift could in fact be a variable. If dshift is a variable, is it possible that what you saw was dshift--? That really means dshift=dshift-1. This would kind of make sense, seeing as this is a loop and in the initializer of the loop dshift is set to 12.


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[This message has been edited by Michael Torrie (edited October 20, 2004).]

[Tom Hanlin]

As Michael says, there are an awful lot of typos in that code. We
might offer more useful assistance if you could cut'n'paste from
the original.

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Tom Hanlin, PowerBASIC Staff
Opinions expressed may not be those of my employer or myself

[Tim Camarda]

Sorry about that. I see comparing from the original there are some typos.
This comes from the Sourceforge Linux NTFS project. http://linux-ntfs.sourceforge.net/nt...mpression.html

for(i=clear_pos-1,lmask=0xFFF,dshift=12;i>=0x10;i>>=1){
lmask >>= 1; /* bit mask for length */
dshift--; /* shift width for delta */
}

My concern with this for-loop is that Im not sure how to translate
it into a PB for-loop equivalent. My theory is: If I could better understand
how the C++ for loop works in this example, I could better understand what
I need to do in the decompression algorithm.

Is it possible to break down the loop into individual components for an
explanation?

Regards, Tim

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[Michael Mattias]

Although I'm sure someone can translate that (but I think they will need, or you will need to have translated the "dshift" and "lmask" variables/functions first), you may not need to translate that 'verb for verb'.

What, in context, does that statement do?

I've seen lots of 'c' code which uses constructs like that to do something simple such as build a powers-of-two or other table used later in the program to mask bits.

MCM

[Tom Hanlin]

for(i=clear_pos-1,lmask=0xFFF,dshift=12;i>=0x10;i>>=1){
    lmask >>= 1; /* bit mask for length */
    dshift--; /* shift width for delta */
}

i = clear_pos - 1
lmask = &HFFF
dshift = 12
DO WHILE i >= &H10
    SHIFT RIGHT lmask, 1  ' bit mask for length
    DECR dshift           ' shift width for delta
    SHIFT RIGHT i, 1
LOOP

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Tom Hanlin, PowerBASIC Staff
Opinions expressed may not be those of my employer or myself

[Tim Camarda]

Many thanks to all those that replied, and special thanks to Tom for
translating the C++ to Power Basic.

I can understand now how the C++ for loop is working.

Again, Thanks all for your time!

Tim

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