I have this code in Qt c++
const unsigned char *packed = reinterpret_cast<const unsigned char*>(data.constData());
res.type = static_cast<int>(packed[0]);
res.period = static_cast<int>(packed[1]);
res.rate = static_cast<qint16>(packed[2] | (packed[3] << 8)) / 100.;
res.edge = static_cast<qint16>(packed[4] | (packed[5] << 8)) / 100.;
return res;
How to convert it from c++ to php
I try this:
$a = unpack ("C*", $data);
$eventList = [];
for ($i=0; $i < $a[1]; $i++)
{
$event = array ();
$index = $i * 6 + 2;
$event["type"] = $a[$index];
$event["period"] = $a[$index+1];
$event["rate"] = ($a[$index+2] | ($a[$index+3] << 8)) / 100;
$event["edge"] = ($a[$index+4] | ($a[$index+5] << 8)) / 100;
}
Edge conver wrong
Very big value.
[edge] => 650.86
must be -4.5
Type, period and rate is good;
Help me please
Don't know the exact answer but some of possible ways to solve the problem:
Check $a[$index+4] and $a[$index+5] value by using var_dump to get its value and type:
var_dump($a[$index+4]);
var_dump($a[$index+5]);
is the data type and its value as expected? Probably good idea is to check as above all data before/after calculation to exactly know what you are dealing with.
Double check your conversion type, perhaps you should't use C* but other, perhaps S or s?
conversion types
If you need type conversion in php you can check how it is done here: Type Juggling and Casting
Note that in PHP you can use a string with ASCII digit that can be treated as digit for calculations:
$foo = 5 * "10 Little Piggies"; // $foo is integer (50)
Which is something you probably don't want.
If you expect negative value but you get positive you have problem because your'e not setting MSB by shifting bits:
The MSB can also correspond to the sign bit of a signed binary number
read-wiki
in case packed[5] should be negative but it isn't
If this not helps then provide data sample and expected values for Edge, Type, period and rate.
I've got this spot of code that seems it could be done cleaner with pure math (perhaps a logarigthms?). Can you help me out?
The code finds the first power of 2 greater than a given input. For example, if you give it 500, it returns 9, because 2^9 = 512 > 500. 2^8 = 256, would be too small because it's less than 500.
function getFactor($iMaxElementsPerDir)
{
$aFactors = range(128, 1);
foreach($aFactors as $i => $iFactor)
if($iMaxElementsPerDir > pow(2, $iFactor) - 1)
break;
if($i == 0)
return false;
return $aFactors[$i - 1];
}
The following holds true
getFactor(500) = 9
getFactor(1000) = 10
getFactor(2500) = 12
getFactor(5000) = 13
You can get the same effect by shifting the bits in the input to the right and checking against 0. Something like this.
i = 1
while((input >> i) != 0)
i++
return i
The same as jack but shorter. Log with base 2 is the reverse function of 2^x.
echo ceil(log(500, 2));
If you're looking for a "math only" solution (that is a single expression or formula), you can use log() and then take the ceiling value of its result:
$factors = ceil(log(500) / log(2)); // 9
$factors = ceil(log(5000) / log(2)); // 13
I seem to have not noticed that this function accepts a second argument (since PHP 4.3) with which you can specify the base; though internally the same operation is performed, it does indeed make the code shorter:
$factors = ceil(log(500, 2)); // 9
To factor in some inaccuracies, you may need some tweaking:
$factors = floor(log($nr - 1, 2)) + 1;
There are a few ways to do this.
Zero all but the most significant bit of the number, maybe like this:
while (x & x-1) x &= x-1;
and look the answer up in a table. Use a table of length 67 and mod your power of two by 67.
Binary search for the high bit.
If you're working with a floating-point number, inspect the exponent field. This field contains 1023 plus your answer, except in the case where the number is a perfect power of two. You can detect the perfect power case by checking whether the significand field is exactly zero.
If you aren't working with a floating-point number, convert it to floating-point and look at the exponent like in 3. Check for a power of two by testing (x & x-1) == 0 instead of looking at the significand; this is true exactly when x is a power of two.
Note that log(2^100) is the same double as log(nextafter(2^100, 1.0/0.0)), so any solution based on floating-point natural logarithms will fail.
Here's (nonconformant C++, not PHP) code for 4:
int ceillog2(unsigned long long x) {
if (x < 2) return x-1;
double d = x-1;
int ans = (long long &)d >> 52;
return ans - 1022;
}
I just found the similar_text function and was playing around with it, but the percentage output always suprises me. See the examples below.
I tried to find information on the algorithm used as mentioned on php: similar_text()Docs:
<?php
$p = 0;
similar_text('aaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//66.666666666667
//Since 5 out of 10 chars match, I would expect a 50% match
similar_text('aaaaaaaaaaaaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//40
//5 out of 20 > not 25% ?
similar_text('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//9.5238095238095
//5 out of 100 > not 5% ?
//Example from PHP.net
//Why is turning the strings around changing the result?
similar_text('PHP IS GREAT', 'WITH MYSQL', $p);
echo $p . "<hr>"; //27.272727272727
similar_text('WITH MYSQL', 'PHP IS GREAT', $p);
echo $p . "<hr>"; //18.181818181818
?>
Can anybody explain how this actually works?
Update:
Thanks to the comments I found that the percentage is actually calculated using the number of similar charactors * 200 / length1 + lenght 2
Z_DVAL_PP(percent) = sim * 200.0 / (t1_len + t2_len);
So that explains why the percenatges are higher then expected. With a string with 5 out of 95 it turns out 10, so that I can use.
similar_text('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//10
//5 out of 95 = 5 * 200 / (5 + 95) = 10
But I still cant figure out why PHP returns a different result on turning the strings around. The JS code provided by dfsq doesn't do this. Looking at the source code in PHP I can only find a difference in the following line, but i'm not a c programmer. Some insight in what the difference is, would be appreciated.
In JS:
for (l = 0;(p + l < firstLength) && (q + l < secondLength) && (first.charAt(p + l) === second.charAt(q + l)); l++);
In PHP: (php_similar_str function)
for (l = 0; (p + l < end1) && (q + l < end2) && (p[l] == q[l]); l++);
Source:
/* {{{ proto int similar_text(string str1, string str2 [, float percent])
Calculates the similarity between two strings */
PHP_FUNCTION(similar_text)
{
char *t1, *t2;
zval **percent = NULL;
int ac = ZEND_NUM_ARGS();
int sim;
int t1_len, t2_len;
if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "ss|Z", &t1, &t1_len, &t2, &t2_len, &percent) == FAILURE) {
return;
}
if (ac > 2) {
convert_to_double_ex(percent);
}
if (t1_len + t2_len == 0) {
if (ac > 2) {
Z_DVAL_PP(percent) = 0;
}
RETURN_LONG(0);
}
sim = php_similar_char(t1, t1_len, t2, t2_len);
if (ac > 2) {
Z_DVAL_PP(percent) = sim * 200.0 / (t1_len + t2_len);
}
RETURN_LONG(sim);
}
/* }}} */
/* {{{ php_similar_str
*/
static void php_similar_str(const char *txt1, int len1, const char *txt2, int len2, int *pos1, int *pos2, int *max)
{
char *p, *q;
char *end1 = (char *) txt1 + len1;
char *end2 = (char *) txt2 + len2;
int l;
*max = 0;
for (p = (char *) txt1; p < end1; p++) {
for (q = (char *) txt2; q < end2; q++) {
for (l = 0; (p + l < end1) && (q + l < end2) && (p[l] == q[l]); l++);
if (l > *max) {
*max = l;
*pos1 = p - txt1;
*pos2 = q - txt2;
}
}
}
}
/* }}} */
/* {{{ php_similar_char
*/
static int php_similar_char(const char *txt1, int len1, const char *txt2, int len2)
{
int sum;
int pos1, pos2, max;
php_similar_str(txt1, len1, txt2, len2, &pos1, &pos2, &max);
if ((sum = max)) {
if (pos1 && pos2) {
sum += php_similar_char(txt1, pos1,
txt2, pos2);
}
if ((pos1 + max < len1) && (pos2 + max < len2)) {
sum += php_similar_char(txt1 + pos1 + max, len1 - pos1 - max,
txt2 + pos2 + max, len2 - pos2 - max);
}
}
return sum;
}
/* }}} */
Source in Javascript: similar text port to javascript
This was actually a very interesting question, thank you for giving me a puzzle that turned out to be very rewarding.
Let me start out by explaining how similar_text actually works.
Similar Text: The Algorithm
It's a recursion based divide and conquer algorithm. It works by first finding the longest common string between the two inputs and breaking the problem into subsets around that string.
The examples you have used in your question, actually all perform only one iteration of the algorithm. The only ones not using one iteration and the ones giving different results are from the php.net comments.
Here is a simple example to understand the main issue behind simple_text and hopefully give some insight into how it works.
Similar Text: The Flaw
eeeefaaaaafddddd
ddddgaaaaagbeeee
Iteration 1:
Max = 5
String = aaaaa
Left : eeeef and ddddg
Right: fddddd and geeeee
I hope the flaw is already apparent. It will only check directly to the left and to the right of the longest matched string in both input strings. This example
$s1='eeeefaaaaafddddd';
$s2='ddddgaaaaagbeeee';
echo similar_text($s1, $s2).'|'.similar_text($s2, $s1);
// outputs 5|5, this is due to Iteration 2 of the algorithm
// it will fail to find a matching string in both left and right subsets
To be honest, I'm uncertain how this case should be treated. It can be seen that only 2 characters are different in the string.
But both eeee and dddd are on opposite ends of the two strings, uncertain what NLP enthusiasts or other literary experts have to say about this specific situation.
Similar Text: Inconsistent results on argument swapping
The different results you were experiencing based on input order was due to the way the alogirthm actually behaves (as mentioned above).
I'll give a final explination on what's going on.
echo similar_text('test','wert'); // 1
echo similar_text('wert','test'); // 2
On the first case, there's only one Iteration:
test
wert
Iteration 1:
Max = 1
String = t
Left : and wer
Right: est and
We only have one iteration because empty/null strings return 0 on recursion. So this ends the algorithm and we have our result: 1
On the second case, however, we are faced with multiple Iterations:
wert
test
Iteration 1:
Max = 1
String = e
Left : w and t
Right: rt and st
We already have a common string of length 1. The algorithm on the left subset will end in 0 matches, but on the right:
rt
st
Iteration 1:
Max = 1
String = t
Left : r and s
Right: and
This will lead to our new and final result: 2
I thank you for this very informative question and the opportunity to dabble in C++ again.
Similar Text: JavaScript Edition
The short answer is: The javascript code is not implementing the correct algorithm
sum += this.similar_text(first.substr(0, pos2), second.substr(0, pos2));
Obviously it should be first.substr(0,pos1)
Note: The JavaScript code has been fixed by eis in a previous commit. Thanks #eis
Demystified!
It would indeed seem the function uses different logic depending of the parameter order. I think there are two things at play.
First, see this example:
echo similar_text('test','wert'); // 1
echo similar_text('wert','test'); // 2
It seems to be that it is testing "how many times any distinct char on param1 is found in param2", and thus result would be different if you swap the params around. It has been reported as a bug, which has been closed as "working as expected".
Now, the above is the same for both PHP and javascript implementations - paremeter order has an impact, so saying that JS code wouldn't do this is wrong. This is argued in the bug entry as intended behaviour.
Second - what doesn't seem correct is the MYSQL/PHP word example. With that, javascript version gives 3 irrelevant of the order of params, whereas PHP gives 2 and 3 (and due to that, percentage is equally different). Now, the phrases "PHP IS GREAT" and "WITH MYSQL" should have 5 characters in common, irrelevant of which way you compare: H, I, S and T, one each, plus one for empty space. In order they have 3 characters, 'H', ' ' and 'S', so if you look at the ordering, correct answer should be 3 both ways. I modified the C code to a runnable version, and added some output, so one can see what is happening there (codepad link):
#include<stdio.h>
/* {{{ php_similar_str
*/
static void php_similar_str(const char *txt1, int len1, const char *txt2, int len2, int *pos1, int *pos2, int *max)
{
char *p, *q;
char *end1 = (char *) txt1 + len1;
char *end2 = (char *) txt2 + len2;
int l;
*max = 0;
for (p = (char *) txt1; p < end1; p++) {
for (q = (char *) txt2; q < end2; q++) {
for (l = 0; (p + l < end1) && (q + l < end2) && (p[l] == q[l]); l++);
if (l > *max) {
*max = l;
*pos1 = p - txt1;
*pos2 = q - txt2;
}
}
}
}
/* }}} */
/* {{{ php_similar_char
*/
static int php_similar_char(const char *txt1, int len1, const char *txt2, int len2)
{
int sum;
int pos1, pos2, max;
php_similar_str(txt1, len1, txt2, len2, &pos1, &pos2, &max);
if ((sum = max)) {
if (pos1 && pos2) {
printf("txt here %s,%s\n", txt1, txt2);
sum += php_similar_char(txt1, pos1,
txt2, pos2);
}
if ((pos1 + max < len1) && (pos2 + max < len2)) {
printf("txt here %s,%s\n", txt1+ pos1 + max, txt2+ pos2 + max);
sum += php_similar_char(txt1 + pos1 + max, len1 - pos1 - max,
txt2 + pos2 + max, len2 - pos2 - max);
}
}
return sum;
}
/* }}} */
int main(void)
{
printf("Found %d similar chars\n",
php_similar_char("PHP IS GREAT", 12, "WITH MYSQL", 10));
printf("Found %d similar chars\n",
php_similar_char("WITH MYSQL", 10,"PHP IS GREAT", 12));
return 0;
}
the result is output:
txt here PHP IS GREAT,WITH MYSQL
txt here P IS GREAT, MYSQL
txt here IS GREAT,MYSQL
txt here IS GREAT,MYSQL
txt here GREAT,QL
Found 3 similar chars
txt here WITH MYSQL,PHP IS GREAT
txt here TH MYSQL,S GREAT
Found 2 similar chars
So one can see that on the first comparison, the function found 'H', ' ' and 'S', but not 'T', and got the result of 3. The second comparison found 'I' and 'T' but not 'H', ' ' or 'S', and thus got the result of 2.
The reason for these results can be seen from the output: algorithm takes the first letter in the first string that second string contains, counts that, and throws away the chars before that from the second string. That is why it misses the characters in-between, and that's the thing causing the difference when you change the character order.
What happens there might be intentional or it might not. However, that's not how javascript version works. If you print out the same things in the javascript version, you get this:
txt here: PHP, WIT
txt here: P IS GREAT, MYSQL
txt here: IS GREAT, MYSQL
txt here: IS, MY
txt here: GREAT, QL
Found 3 similar chars
txt here: WITH, PHP
txt here: W, P
txt here: TH MYSQL, S GREAT
Found 3 similar chars
showing that javascript version does it in a different way. What the javascript version does is that it finds 'H', ' ' and 'S' being in the same order in the first comparison, and the same 'H', ' ' and 'S' also on the second one - so in this case the order of params doesn't matter.
As the javascript is meant to duplicate the code of PHP function, it needs to behave identically, so I submitted bug report based on analysis of #Khez and the fix, which has been merged now.
first String = aaaaaaaaaa = 10 letters
second String = aaaaa = 5 letters
first five letters are similar
a+a
a+a
a+a
a+a
a+a
a
a
a
a
a
( <similar_letters> * 200 ) / (<letter_count_first_string> + <letter_count_second_string>)
( 5 * 200 ) / (10 + 5);
= 66.6666666667
Description
int similar_text ( string $first , string $second [, float &$percent ] )
This calculates the similarity between two strings as described in Oliver [1993]. Note that this implementation does not use a stack as in Oliver's pseudo code, but recursive calls which may or may not speed up the whole process. Note also that the complexity of this algorithm is O(N**3) where N is the length of the longest string.
Parameters
first
The first string.
second
The second string.
percent
By passing a reference as third argument, similar_text() will calculate the similarity in percent for you.
#include <fstream>
#include <iostream>
using namespace std;
bool find_in_file(char*);
void insert_in_file(char*);
inline bool isNull(char* word);
int main()
{
char word[25];
for(int i = 0; i < 10; i++)
{
cin >> word;
if( find_in_file(word) )
cout << "found" << endl;
else
insert_in_file(word);
}
system("pause");
}
bool find_in_file(char* word)
{
ifstream file;
file.open("file.dat", ios::in);
char contents[655][25] = {0};
file.read(reinterpret_cast<char*>(contents), 16*1024);
file.close();
int i = 0;
while( !isNull(contents[i]) )
{
if( strcmp(contents[i], word) == 0)
return true;
if( strcmp(contents[i], word) < 0 )
i = 2*i + 2;
else
i = 2*i + 1;
}
return false;
}
void insert_in_file(char* word)
{
fstream file;
file.open("file.dat", ios::in | ios::binary);
char contents[655][25] = {0};
file.read(reinterpret_cast<char*>(contents), 16*1024);
file.close();
file.open("file.dat", ios::in | ios::out | ios::binary);
if( isNull(contents[0]) )
{
file.write(word, 25);
file.close();
return;
}
int parent;
int current = 0;
while( !isNull(contents[current]) )
{
parent = current;
if( strcmp( contents[current], word ) < 0 )
current = current*2 + 2;
else if ( strcmp( contents[current], word ) > 0)
current = current*2 + 1;
else
return;
}
int insertAt;
if( strcmp(contents[parent], word ) < 0 )
insertAt = parent*2 + 2;
else
insertAt = parent*2 + 1;
file.seekp(insertAt*25, ios_base::beg);
file.write(reinterpret_cast<const char*>(word), 25);
file.close();
}
inline bool isNull(char* word)
{
return word[0] == 0;
}
The above code implements a binary search tree on file. It uses char arrays of length 25 as nodes. It assumes a size of around 16K as max for the file. The tree is stored in this format:
0 root
1 left child of root - L
2 right child of root - R
3 left child of L - LL
4 right child of L - LR
5 left child of R - RL
6 right child of R - RR
and so on. In the absence of a child, an empty node is inserted. Now I have to do the same thing in PHP. How is it possible since as far as I know, PHP does not provide binary file access. Eagerly looking forward to your responses :)
edit: If I write an integer to file in binary mode, c/c++ will write 4 bytes regardless of the value stored in that integer. PHP will write the plain integer value in file, that is, 0 if the value is 0 and 100 if it is 100. This raises problems when using seek because I dont know the specific number of bytes to move the put pointer. Or in this case, I am writing character arrays of fixed length = 25. How can I do this in php since the variables dont have a type at all?
PHP does provide binary file access. Use fopen() and specify 'b' in the mode field.
To perform random access (i.e. read/write), you should specify 'r+' in the mode field (or 'w+', 'x+' or 'a+', depending on precisely what you want to do).
To actually write binary data (rather than textual representations of that data), use fwrite() and pack().
From php documentation:
In contrast, you can also use 'b' to force binary mode, which will not
translate your data. To use these flags, specify either 'b' or 't' as
the last character of the mode parameter.
What exactly do you mean when you say that php doesn't provide binary file access?
I have these possible bit flags.
1, 2, 4, 8, 16, 64, 128, 256, 512, 2048, 4096, 16384, 32768, 65536
So each number is like a true/false statement on the server side. So if the first 3 items, and only the first 3 items are marked "true" on the server side, the web service will return a 7. Or if all 14 items above are true, I would still get a single number back from the web service which is is the sum of all those numbers.
What is the best way to handle the number I get back to find out which items are marked as "true"?
Use a bit masking operator. In the C language:
X & 8
is true, if the "8"s bit is set.
You can enumerate the bit masks, and count how many are set.
If it really is the case that the entire word contains bits, and you want to simply
compute how many bits are set, you want in essence a "population count". The absolute
fastest way to get a population count is to execute a native "popcnt" usually
available in your machine's instruction set.
If you don't care about space, you can set up a array countedbits[...] indexed by your value with precomputed bit counts. Then a single memory access computes your bit count.
Often used is just plain "bit twiddling code" that computes bit counts:
(Kernigan's method):
unsigned int v; // count the number of bits set in v
unsigned int c; // c accumulates the total bits set in v
for (c = 0; v; c++)
{
v &= v - 1; // clear the least significant bit set
}
(parallel bit summming, 32 bits)
v = v - ((v >> 1) & 0x55555555); // reuse input as temporary
v = (v & 0x33333333) + ((v >> 2) & 0x33333333); // temp
c = ((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; // count
If you haven't seen the bit twiddling hacks before, you're in for a treat.
PHP, being funny, may do funny things with some of this arithmetic.
if (7 & 1) { // if bit 1 is set in returned number (7)
}
Thought the question is old might help someone else. I am putting the numbers in binary as its clearer to understand. The code had not been tested but hope the logic is clear. The code is PHP specific.
define('FLAG_A', 0b10000000000000);
define('FLAG_B', 0b01000000000000);
define('FLAG_C', 0b00100000000000);
define('FLAG_D', 0b00010000000000);
define('FLAG_E', 0b00001000000000);
define('FLAG_F', 0b00000100000000);
define('FLAG_G', 0b00000010000000);
define('FLAG_H', 0b00000001000000);
define('FLAG_I', 0b00000000100000);
define('FLAG_J', 0b00000000010000);
define('FLAG_K', 0b00000000001000);
define('FLAG_L', 0b00000000000100);
define('FLAG_M', 0b00000000000010);
define('FLAG_N', 0b00000000000001);
function isFlagSet($Flag,$Setting,$All=false){
$setFlags = $Flag & $Setting;
if($setFlags and !$All) // at least one of the flags passed is set
return true;
else if($All and ($setFlags == $Flag)) // to check that all flags are set
return true;
else
return false;
}
Usage:
if(isFlagSet(FLAG_A,someSettingsVariable)) // eg: someSettingsVariable = 0b01100000000010
if(isFlagSet(FLAG_A | FLAG_F | FLAG_L,someSettingsVariable)) // to check if atleast one flag is set
if(isFlagSet(FLAG_A | FLAG_J | FLAG_M | FLAG_D,someSettingsVariable, TRUE)) // to check if all flags are set
One way would be to loop through your number, left-shifting it (ie divide by 2) and compare the first bit with 1 using the & operand.
As there is no definite answer with php code, I add this working example:
// returns array of numbers, so for 7 returns array(1,2,4), etc..
function get_bits($decimal) {
$scan = 1;
$result = array();
while ($decimal >= $scan){
if ($decimal & $scan) $result[] = $scan;
$scan<<=1;
}
return $result;
}