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Re: [PATCH] Optimize 'a ' as single char string too
- From: Tobias Burnus <tobias dot burnus at physik dot fu-berlin dot de>
- To: Steve Kargl <sgk at troutmask dot apl dot washington dot edu>, Jakub Jelinek <jakub at redhat dot com>, fortran at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Wed, 14 Jul 2010 11:02:29 +0200
- Subject: Re: [PATCH] Optimize 'a ' as single char string too
On Tue, Jul 13, 2010 at 11:07:15PM -0700, Steve Kargl wrote:
> If you haven't committed your patch based on my OK,
> can you hold off a bit? I have received a query about
> whether trailing whitespace in a string needs to be
> omitted by a TRIM call.
I don't quite understand the question
"whether trailing whitespace in a string needs to be omitted by
a TRIM call."
Assuming your "whitespace" means " " (a space/blank), I would say
a) TRIM should do this as the result is:
"The value of the result is the same as STRING except any
trailing blanks are removed."
b) For character comparison, TRIM does not play any role, cf.
"For a character relational intrinsic operation, the operands are
compared one character at a time in order, beginning with the first
character of each character operand. If the operands are of unequal
length, the shorter operand is treated as if it were extended on
the right with blanks to the length of the longer operand. If both
x1 and x2 are of zero length, x1 is equal to x2; if every character
of x1 is the same as the character in the corresponding position in
x2, x1 is equal to x2. Otherwise, at the first position where the
character operands differ, the character operand x1 is considered
to be less than x2 if the character value of x1 at this position
precedes the value of x2 in the collating sequence (1.3); x1 is
greater than x2 if the character value of x1 at this position
follows the value of x2 in the collating sequence."
(F2008, 126.96.36.199.1 Interpretation of relational intrinsic operations)
Thus, the optimization of ignoring the tailing blanks for
if (c .eq. 'a ') call abort
seems to be fine.