Re: Declaration to get 8-bit (or 16-bit) integer?

Clive Page wrote:
In message <epohfj$j3m$1@xxxxxxxxxxxxxxxxxx>, Paul van Delst <Paul.vanDelst@xxxxxxxx> writes
But seriously, I use this for the multi-byte case:

MODULE Endian_Utility
USE Type_Kinds
IMPLICIT NONE
CONTAINS
FUNCTION Big_Endian()
INTEGER(Short) :: Source = 1_Short
LOGICAL :: Big_Endian
Big_Endian = .FALSE.
IF ( IACHAR(TRANSFER(Source,'a')) == 0 ) Big_Endian = .TRUE.
END FUNCTION Big_Endian
....
END MODULE Endian_Utility

That looks very similar to a module that I posted some years ago. If only I could remember how it worked :-)

Ha! I was going to write the exact same comment but I figured too much tongue in cheek would detract from my post's utility (such as it was). :oD

I probably did crib it from you via clf - most of my generally useful tools I've acquired via clf posts.


Now to a more difficult topic: how to get the effect of LOGICAL*1

What for? :o)

If you want a really large array of logicals, e.g. flags for bad pixels in a huge image, then the difference between 1-byte and 4-byte data can be significant.

Yeah, I was just pulling yer proverbial about that. But, wouldn't an array of integer(byte) achieve the same purpose? Depending on how you name your mask array, values of true/false or 0/1 can be ambiguous either way. But parameters would solve that:

use type_kinds ! definition of integer byte kind in here
integer(byte), parameter :: bad_pixel = 0_byte
integer(byte), parameter :: good_pixel = 1_byte
......
integer, parameter :: n = 100000
......
integer :: image(n,n) ! Assume default for image
integer(byte) :: mask(n,n)

where (mask == good_pixel)
..process pixels in image
end where


It's not as succinct as something like:


use type_kinds
integer, parameter :: n = 100000
......
integer :: image(n,n) ! Assume default for image
logical(byte) :: good_pixels(n,n) ! Assuming you can do this

where (good_pixels)
..process pixels in image
end where


but it's portable. :o)


Does the difference between doing
where (mask == good_pixel)
or
where (good_pixels)
incur any performance penalties?

cheers,

paulv

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