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Doc Bug #73770 Truth table errors
Submitted: 2016-12-17 09:12 UTC Modified: 2016-12-17 11:41 UTC
From: rjhdby@php.net Assigned:
Status: Open Package: COM related
PHP Version: Irrelevant OS:
Private report: No CVE-ID: None
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 [2016-12-17 09:12 UTC] rjhdby@php.net
Description:
------------
---
From manual page: http://www.php.net/function.variant-imp
---

Truth table for bitwise implication is not correct.

Must be
If left is	If right is	then the result is
TRUE	TRUE	TRUE
TRUE	FALSE	TRUE   >> FALSE
TRUE	NULL	TRUE   >> FALSE
FALSE	TRUE	TRUE
FALSE	FALSE	TRUE
FALSE	NULL	TRUE
NULL	TRUE	TRUE
NULL	FALSE	NULL   >> TRUE
NULL	NULL	NULL   >> TRUE



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 [2016-12-17 11:41 UTC] requinix@php.net
-Package: Documentation problem +Package: COM related
 [2016-12-17 11:41 UTC] requinix@php.net
When I try

foreach ([true, false, null] as $i)
foreach ([true, false, null] as $j) {
  $v = variant_imp($i, $j);
  $v = (variant_get_type($v) == VT_NULL ? null : (int)$v);
  printf("variant_imp(%s, %s) = %s\n", json_encode($i), json_encode($j), json_encode($v));
}

I get

variant_imp(true, true) = -1
variant_imp(true, false) = 0
variant_imp(true, null) = null
variant_imp(false, true) = -1
variant_imp(false, false) = -1
variant_imp(false, null) = -1
variant_imp(null, true) = -1
variant_imp(null, false) = null
variant_imp(null, null) = null

true->false should be false ("true implies false" is wrong). true->null, null->false, and null->null should all be unknown.
 [2016-12-17 18:19 UTC] andrewgrom at rambler dot ru
The problem is more complex. It is bitwise operation.

$T = new VARIANT(255,VT_UI1);
$F = new VARIANT(0,VT_UI1);
$N = new VARIANT(VT_NULL,VT_UI1);

echo variant_imp($T, $F).PHP_EOL;
echo variant_imp($T, $T).PHP_EOL;
echo variant_imp($T, $N).PHP_EOL;
echo variant_imp($F, $F).PHP_EOL;
echo variant_imp($F, $T).PHP_EOL;
echo variant_imp($F, $N).PHP_EOL;
echo variant_imp($N, $F).PHP_EOL;
echo variant_imp($N, $T).PHP_EOL;
echo variant_imp($N, $N).PHP_EOL;

0
255
1  <--- Not null
255
255
255
254 <--- Not null. True in all bits except one
255 
255 <--- Totaly not null. True in all bits
 [2016-12-17 19:21 UTC] andrewgrom at rambler dot ru
My mistake in previsious comment.
You are right,
"true->false should be false ("true implies false" is wrong). true->null, null->false, and null->null should all be unknown."
 
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