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From: "cjashfor at linux dot ibm.com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/94833] New: vec_first_match_index does not function as
 described in its description
Date: Tue, 28 Apr 2020 20:43:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94833

            Bug ID: 94833
           Summary: vec_first_match_index does not function as described
                    in its description
           Product: gcc
           Version: 9.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cjashfor at linux dot ibm.com
                CC: carll at gcc dot gnu.org
  Target Milestone: ---

The description in the 64-bit ELF V2 ABI Specification 1.4 says this:

Purpose:
Performs a comparison of equality on each of the corresponding elements of =
ARG1
and
ARG2, and returns the first position of equality.
Result value:
Returns the element index of the position of the first character match. If =
no
match, returns
the number of characters as an element count in the vector argument.


Note that it doesn't make any mention of null or EOS characters.  By the
description, it ought to compare null characters for equality as well, but =
it
doesn't.  It seems to terminate the comparison when it sees that there's a =
null
(0x00) in one of the two vector elements.  Here's my test case:

#include <stdio.h>
#include <altivec.h>

int main() {
        vector unsigned char v1 =3D { 0, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40 };

        vector unsigned char vec_0s =3D vec_splats((unsigned char)0x0);

        int first_match_index =3D vec_first_match_index(v1, vec_0s);
        if (first_match_index !=3D 0) {
                printf("Failed: first_match_index should be 0 but it is %d\=
n",
first_match_index);
        } else {
                printf("Passed\n");
        }
        return 0;
}


I compiled it with -mcpu=3Dpower9 -maltivec.  When the test case is run, it=
 says
this:

Failed: first_match_index should be 0 but it is 16

I don't know whether the description is incomplete or the function isn't
implemented correctly.=