Cast unsigned long into signed short in PHP
In some other languages this problem is a matter of a simple cast. In PHP there's no such concept as all integers have the very same type (signed long long or signed long, architecture-dependent). Yet there are cases where you have to do that. E.g. unpack() cannot read signed long little endian byte order, only unsigned.
So, given an imaginary 32bit unsigned integer 4294967295, how do I get a value for an imaginary signed 32bit integer from it? (That's -1.)
For example, this can be done with pack/unpack, but this seems suboptimal to me.
Is there a better way?
How about 32bit versions of PHP? (They tend to solve this problem "automatically" with an integer overflow, but I rather not to use this architecture-dependent workarounds. Background.)
php
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
|
show 1 more comment
In some other languages this problem is a matter of a simple cast. In PHP there's no such concept as all integers have the very same type (signed long long or signed long, architecture-dependent). Yet there are cases where you have to do that. E.g. unpack() cannot read signed long little endian byte order, only unsigned.
So, given an imaginary 32bit unsigned integer 4294967295, how do I get a value for an imaginary signed 32bit integer from it? (That's -1.)
For example, this can be done with pack/unpack, but this seems suboptimal to me.
Is there a better way?
How about 32bit versions of PHP? (They tend to solve this problem "automatically" with an integer overflow, but I rather not to use this architecture-dependent workarounds. Background.)
php
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
1
"Getting a signed 16bit integer" from it doesn't make a whole lot of sense, since as you say, PHP doesn't have that kind of number. All you'd get is another 32/64bit integer with a different value. You want to interpret the byte representation of the 32bit signed int as 16bit int…?
– deceze♦
Nov 13 '18 at 0:58
'interpret the byte representation of the 32bit unsigned int as 16bit signed int' - that's about it (this issue)
– sanmai
Nov 13 '18 at 0:59
so just fix your code: github.com/pear/OLE/blob/… just use another formatunpack("v", fread($fh, 4));php.net/manual/en/function.pack.php
– Alex
Nov 13 '18 at 1:19
@Alex do you propose to unpack into a signed value and hope for the best, e.g. for an overflow? What if it does not happen?
– sanmai
Nov 13 '18 at 1:33
I propose to have proper design and defined data flow. Your data is coming from some stream, and the only thing we should do - read stream data the way it was designed.
– Alex
Nov 13 '18 at 1:42
|
show 1 more comment
In some other languages this problem is a matter of a simple cast. In PHP there's no such concept as all integers have the very same type (signed long long or signed long, architecture-dependent). Yet there are cases where you have to do that. E.g. unpack() cannot read signed long little endian byte order, only unsigned.
So, given an imaginary 32bit unsigned integer 4294967295, how do I get a value for an imaginary signed 32bit integer from it? (That's -1.)
For example, this can be done with pack/unpack, but this seems suboptimal to me.
Is there a better way?
How about 32bit versions of PHP? (They tend to solve this problem "automatically" with an integer overflow, but I rather not to use this architecture-dependent workarounds. Background.)
php
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
In some other languages this problem is a matter of a simple cast. In PHP there's no such concept as all integers have the very same type (signed long long or signed long, architecture-dependent). Yet there are cases where you have to do that. E.g. unpack() cannot read signed long little endian byte order, only unsigned.
So, given an imaginary 32bit unsigned integer 4294967295, how do I get a value for an imaginary signed 32bit integer from it? (That's -1.)
For example, this can be done with pack/unpack, but this seems suboptimal to me.
Is there a better way?
How about 32bit versions of PHP? (They tend to solve this problem "automatically" with an integer overflow, but I rather not to use this architecture-dependent workarounds. Background.)
php
php
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
edited Nov 19 '18 at 5:36
sanmai
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
asked Nov 13 '18 at 0:55
sanmaisanmai
9,93674064
9,93674064
1
"Getting a signed 16bit integer" from it doesn't make a whole lot of sense, since as you say, PHP doesn't have that kind of number. All you'd get is another 32/64bit integer with a different value. You want to interpret the byte representation of the 32bit signed int as 16bit int…?
– deceze♦
Nov 13 '18 at 0:58
'interpret the byte representation of the 32bit unsigned int as 16bit signed int' - that's about it (this issue)
– sanmai
Nov 13 '18 at 0:59
so just fix your code: github.com/pear/OLE/blob/… just use another formatunpack("v", fread($fh, 4));php.net/manual/en/function.pack.php
– Alex
Nov 13 '18 at 1:19
@Alex do you propose to unpack into a signed value and hope for the best, e.g. for an overflow? What if it does not happen?
– sanmai
Nov 13 '18 at 1:33
I propose to have proper design and defined data flow. Your data is coming from some stream, and the only thing we should do - read stream data the way it was designed.
– Alex
Nov 13 '18 at 1:42
|
show 1 more comment
1
"Getting a signed 16bit integer" from it doesn't make a whole lot of sense, since as you say, PHP doesn't have that kind of number. All you'd get is another 32/64bit integer with a different value. You want to interpret the byte representation of the 32bit signed int as 16bit int…?
– deceze♦
Nov 13 '18 at 0:58
'interpret the byte representation of the 32bit unsigned int as 16bit signed int' - that's about it (this issue)
– sanmai
Nov 13 '18 at 0:59
so just fix your code: github.com/pear/OLE/blob/… just use another formatunpack("v", fread($fh, 4));php.net/manual/en/function.pack.php
– Alex
Nov 13 '18 at 1:19
@Alex do you propose to unpack into a signed value and hope for the best, e.g. for an overflow? What if it does not happen?
– sanmai
Nov 13 '18 at 1:33
I propose to have proper design and defined data flow. Your data is coming from some stream, and the only thing we should do - read stream data the way it was designed.
– Alex
Nov 13 '18 at 1:42
1
1
"Getting a signed 16bit integer" from it doesn't make a whole lot of sense, since as you say, PHP doesn't have that kind of number. All you'd get is another 32/64bit integer with a different value. You want to interpret the byte representation of the 32bit signed int as 16bit int…?
– deceze♦
Nov 13 '18 at 0:58
"Getting a signed 16bit integer" from it doesn't make a whole lot of sense, since as you say, PHP doesn't have that kind of number. All you'd get is another 32/64bit integer with a different value. You want to interpret the byte representation of the 32bit signed int as 16bit int…?
– deceze♦
Nov 13 '18 at 0:58
'interpret the byte representation of the 32bit unsigned int as 16bit signed int' - that's about it (this issue)
– sanmai
Nov 13 '18 at 0:59
'interpret the byte representation of the 32bit unsigned int as 16bit signed int' - that's about it (this issue)
– sanmai
Nov 13 '18 at 0:59
so just fix your code: github.com/pear/OLE/blob/… just use another format
unpack("v", fread($fh, 4)); php.net/manual/en/function.pack.php– Alex
Nov 13 '18 at 1:19
so just fix your code: github.com/pear/OLE/blob/… just use another format
unpack("v", fread($fh, 4)); php.net/manual/en/function.pack.php– Alex
Nov 13 '18 at 1:19
@Alex do you propose to unpack into a signed value and hope for the best, e.g. for an overflow? What if it does not happen?
– sanmai
Nov 13 '18 at 1:33
@Alex do you propose to unpack into a signed value and hope for the best, e.g. for an overflow? What if it does not happen?
– sanmai
Nov 13 '18 at 1:33
I propose to have proper design and defined data flow. Your data is coming from some stream, and the only thing we should do - read stream data the way it was designed.
– Alex
Nov 13 '18 at 1:42
I propose to have proper design and defined data flow. Your data is coming from some stream, and the only thing we should do - read stream data the way it was designed.
– Alex
Nov 13 '18 at 1:42
|
show 1 more comment
1 Answer
1
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oldest
votes
For one, this can be done with pack/unpack:
$value = 4294967295;
$result = unpack("l", pack('L', $value));
var_dump($result[1]); // -1
Try live.
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
add a comment |
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For one, this can be done with pack/unpack:
$value = 4294967295;
$result = unpack("l", pack('L', $value));
var_dump($result[1]); // -1
Try live.
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
add a comment |
For one, this can be done with pack/unpack:
$value = 4294967295;
$result = unpack("l", pack('L', $value));
var_dump($result[1]); // -1
Try live.
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
add a comment |
For one, this can be done with pack/unpack:
$value = 4294967295;
$result = unpack("l", pack('L', $value));
var_dump($result[1]); // -1
Try live.
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
For one, this can be done with pack/unpack:
$value = 4294967295;
$result = unpack("l", pack('L', $value));
var_dump($result[1]); // -1
Try live.
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
answered Nov 19 '18 at 5:36
sanmaisanmai
9,93674064
9,93674064
add a comment |
add a comment |
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1
"Getting a signed 16bit integer" from it doesn't make a whole lot of sense, since as you say, PHP doesn't have that kind of number. All you'd get is another 32/64bit integer with a different value. You want to interpret the byte representation of the 32bit signed int as 16bit int…?
– deceze♦
Nov 13 '18 at 0:58
'interpret the byte representation of the 32bit unsigned int as 16bit signed int' - that's about it (this issue)
– sanmai
Nov 13 '18 at 0:59
so just fix your code: github.com/pear/OLE/blob/… just use another format
unpack("v", fread($fh, 4));php.net/manual/en/function.pack.php– Alex
Nov 13 '18 at 1:19
@Alex do you propose to unpack into a signed value and hope for the best, e.g. for an overflow? What if it does not happen?
– sanmai
Nov 13 '18 at 1:33
I propose to have proper design and defined data flow. Your data is coming from some stream, and the only thing we should do - read stream data the way it was designed.
– Alex
Nov 13 '18 at 1:42