String.unpack - signed 4byte little-endian integer?

thomthom

Thanks for that Dan. That confirmed my suspicion.

Can't one rearrange the bits using ruby? If one use the RUBY_PLATFORM constant to determine if the host is a PPC, when swap the bits with ruby avoiding the need to C dependencies?

Dan Rathbun

@thomthom said:

Can't one rearrange the bits using ruby?

Sure .. remember that Color Integer Conversion code I did awhile back.
That was just swapping bits around.

thomthom

I need to revisit that. Make some le2be and be2le methods.

MartinRinehart

@thomthom said:

Can't one rearrange the bits using ruby? If one use the RUBY_PLATFORM constant to determine if the host is a PPC, when swap the bits with ruby avoiding the need to C dependencies?

Mucking with bits in Ruby is very easy (though performance?). In VisMap I fiddled with bits in JavaScript to encode the string sent to Ruby and in reverse in the Ruby to unencode. Wrote about that in http://www.MartinRinehart.com/models/tutorial/tutorial_bfr.htmlAppendix BFR[/url].

I apologize for the code. It dates back to when I was first writing Ruby, trying to do things the Ruby way.

Dan Rathbun

@dan rathbun said:

@thomthom said:

Can one from ruby find out what the native endian is?
... this page:
http://developer.apple.com/mac/library/documentation/DeveloperTools/gcc-4.0.1/gcc/ARM-Options.html
seems to suggest that the processor itself can run in "an endian mode".

More info...
@unknownuser said:

(http://en.wikipedia.org/wiki/Endian#Bi-endian_hardware)":2fp65ya5]Some architectures (including ARM, PowerPC, Alpha, SPARC V9, MIPS, PA-RISC and IA-64) feature switchable endianness. This feature can improve performance or simplify the logic of networking devices and software. The word bi-endian, said of hardware, denotes the capability to compute or pass data in either of two different endian formats.
...
Note, too, that some nominally bi-endian CPUs may actually employ internal "magic" (as opposed to really switching to a different endianness) in one of their operating modes. For instance, some PowerPC processors in little-endian mode act as little-endian from the point of view of the executing programs but they do not actually store data in memory in little-endian format (multi-byte values are swapped during memory load/store operations).

Dan Rathbun

@thomthom said:

I need to revisit that. Make some le2be and be2le methods.

Hmmm... looking at Array.pack it says "network byte order" is big-endian.

Would something like this work? (you'd need to apply your platform test beforehand)


# singleton method for String
def myStr.swapEndian_to_i( long=true, signed=true )
  arr=[]
  self.each_byte {|byte| arr.unshift(byte) }
  str=arr.join
  if signed
    return ( long ? str.unpack('l') ; str.unpack('s') )
  else # unsigned
    return ( long ? str.unpack('L') ; str.unpack('S') )
  end
end

Further Reading:
Understanding Big and Little Endian Byte Order
Blog: How to convert an integer to little endian or big endian
Apple Dev: Byte Swapping Integers
Endian FAQ

thomthom

Good stuff Dan - thanks for looking into this. I'll look into this as soon as I can. (Just need to get Vertex Tools out the window)

Dan Rathbun

@thomthom said:

Can one from ruby find out what the native endian is?

from the source:

@unknownuser said:

... use WORDS_BIGENDIAN to detect the platform's endian.

WORDS_BIGENDIAN is set in defines.h (line 163,) IF the compiler had defined BIG_ENDIAN (otherwise LITTLE_ENDIAN would have been defined.)

Have a look at pack.c begining line 182:
There is a C function declared called endian() that returns 0|1
.. you'll see how in that block between 182 and 280 how #ifdef DYNAMIC_ENDIAN and #ifdef WORDS_BIGENDIAN are used with the endian() function to control how values are converted.
The endian() function only gets declared if DYNAMIC_ENDIAN is defined.

But you could do something similar in


#include 'ruby.h'
#include 'defines.h'
#ifdef WORDS_BIGENDIAN
  /* define a ruby constant that returns true */
#else
  /* define a ruby constant that returns false */
#endif

Dan Rathbun

Another idea, since on the Mac you have a full Ruby install..
is to see what the compiler -archflags were when Ruby was built for the PPC.

The Config::CONFIG hash contains alot of info:
At console try:
Config::CONFIG['ARCH_FLAG']

or just open the rbconfig.rb file in the arch_sub_folder (ppc-darwinX.X) of the ruby lib folder and manually browse the whole hash for possible info.

Dan Rathbun

TT,

Just posted a Platform module in the SKX forum that has some Pure Ruby Endianess hacks.
http://forums.sketchucation.com/viewtopic.php?f=315&t=29132#p253630

thomthom

That sounds good.
I still haven't been able to look at this. Trying to crunch out Vertex Tools.