Optimize pack()

[nielsdos]

Instead of using lookup tables, we can use a combination of shifts and
byte swapping to achieve the same thing in less cycles and with less
code.

Benchmark files

pack1.php:

for ($i = 0; $i < 10_000_000; ++$i) {
    pack("J", 0x7FFFFFFFFFFFFFFF);
}

pack2.php:

for ($i = 0; $i < 4000000; ++$i) {
    pack("nvc*", 0x1234, 0x5678, 65, 66);
}

Results

On an i7-4790:

Benchmark 1: ./sapi/cli/php pack1.php
  Time (mean ± σ):     408.8 ms ±   3.4 ms    [User: 406.1 ms, System: 1.6 ms]
  Range (min … max):   403.6 ms … 413.6 ms    10 runs

Benchmark 2: ./sapi/cli/php_old pack1.php
  Time (mean ± σ):     451.7 ms ±   7.7 ms    [User: 448.5 ms, System: 2.0 ms]
  Range (min … max):   442.8 ms … 461.2 ms    10 runs

Summary
  ./sapi/cli/php pack1.php ran
    1.11 ± 0.02 times faster than ./sapi/cli/php_old pack1.php

Benchmark 1: ./sapi/cli/php pack2.php
  Time (mean ± σ):     239.3 ms ±   6.0 ms    [User: 236.2 ms, System: 2.3 ms]
  Range (min … max):   233.2 ms … 256.8 ms    12 runs

Benchmark 2: ./sapi/cli/php_old pack2.php
  Time (mean ± σ):     271.9 ms ±   3.3 ms    [User: 269.7 ms, System: 1.3 ms]
  Range (min … max):   267.4 ms … 279.0 ms    11 runs

Summary
  ./sapi/cli/php pack2.php ran
    1.14 ± 0.03 times faster than ./sapi/cli/php_old pack2.php

On an i7-1185G7:

Benchmark 1: ./sapi/cli/php pack1.php
  Time (mean ± σ):     263.7 ms ±   1.8 ms    [User: 262.6 ms, System: 0.9 ms]
  Range (min … max):   261.5 ms … 268.2 ms    11 runs

Benchmark 2: ./sapi/cli/php_old pack1.php
  Time (mean ± σ):     303.3 ms ±   6.5 ms    [User: 300.7 ms, System: 2.3 ms]
  Range (min … max):   297.4 ms … 318.1 ms    10 runs

Summary
  ./sapi/cli/php pack1.php ran
    1.15 ± 0.03 times faster than ./sapi/cli/php_old pack1.php

Benchmark 1: ./sapi/cli/php pack2.php
  Time (mean ± σ):     156.7 ms ±   2.9 ms    [User: 154.7 ms, System: 1.7 ms]
  Range (min … max):   151.6 ms … 164.7 ms    19 runs

Benchmark 2: ./sapi/cli/php_old pack2.php
  Time (mean ± σ):     174.6 ms ±   3.3 ms    [User: 171.9 ms, System: 2.3 ms]
  Range (min … max):   170.7 ms … 180.4 ms    17 runs

Summary
  ./sapi/cli/php pack2.php ran
    1.11 ± 0.03 times faster than ./sapi/cli/php_old pack2.php

[staabm]

maybe a interessting benchmark/test-case for unpack: stomp-php/stomp-php#184

<?php
$file = file_get_contents('FILE');
echo count(unpack('C*', $file)) . "\n";

vs.

<?php
$file = file_get_contents('FILE');
echo strlen($file) . "\n";

using truncate -s 80M FILE.

the strlen() variant is a lot faster

[nielsdos]

maybe a interessting benchmark/test-case for unpack: stomp-php/stomp-php#184

<?php
$file = file_get_contents('FILE');
echo count(unpack('C*', $file)) . "\n";

vs.

<?php
$file = file_get_contents('FILE');
echo strlen($file) . "\n";

using truncate -s 80M FILE.

the strlen() variant is a lot faster

Unpack will always be slower than just strlen. However, your code revealed that repetitions were handled in a slow way where lots of temporary strings were created and then parsed. I opened a PR to fix that particular issue: #18803

[divinity76]

could benchmark

static inline void php_pack(const zval *val, size_t size,
                            php_pack_endianness enc, char *out)
{
    zend_long z = zval_get_long(val);

    if ((enc == PHP_LITTLE_ENDIAN) != MACHINE_LITTLE_ENDIAN) {
        z = PHP_LONG_BSWAP(z);
    }
    memcpy(out, (char*)&z + sizeof(z) - size, size);
}

might be faster

[nielsdos]

Very strangely, my original code with zend_never_inline is slightly faster than master, but your code without zend_never_inline seems to beat that in my test with the 'J' specifier. Testing some more stuff...

[divinity76]

if the performance difference insignificant/marginal, as in hardly even benchmark-able, i would recommend just ignoring it.

I like how this makes pack the code much simpler (assuming it actually works on BE)

[nielsdos]

I think I managed to make the compiler happy and let it make good inlining decisions while keeping the code simple.

For example for this:

for ($i = 0; $i < 10_000_000; ++$i) {
  pack("J", 0x7FFFFFFFFFFFFFFF);
}

On an i7-4790:

Benchmark 1: ./sapi/cli/php pack.php
  Time (mean ± σ):     408.8 ms ±   3.4 ms    [User: 406.1 ms, System: 1.6 ms]
  Range (min … max):   403.6 ms … 413.6 ms    10 runs
 
Benchmark 2: ./sapi/cli/php_old pack.php
  Time (mean ± σ):     451.7 ms ±   7.7 ms    [User: 448.5 ms, System: 2.0 ms]
  Range (min … max):   442.8 ms … 461.2 ms    10 runs
 
Summary
  ./sapi/cli/php pack.php ran
    1.11 ± 0.02 times faster than ./sapi/cli/php_old pack.php

And for this:

for ($i=0;$i<4000000;$i++)
pack("nvc*", 0x1234, 0x5678, 65, 66);

On the same machine:

Benchmark 1: ./sapi/cli/php pack.php
  Time (mean ± σ):     239.3 ms ±   6.0 ms    [User: 236.2 ms, System: 2.3 ms]
  Range (min … max):   233.2 ms … 256.8 ms    12 runs
 
Benchmark 2: ./sapi/cli/php_old pack.php
  Time (mean ± σ):     271.9 ms ±   3.3 ms    [User: 269.7 ms, System: 1.3 ms]
  Range (min … max):   267.4 ms … 279.0 ms    11 runs
 
Summary
  ./sapi/cli/php pack.php ran
    1.14 ± 0.03 times faster than ./sapi/cli/php_old pack.php

Let's hope it's reproducible

[nielsdos]

It's consistent on my laptop. Squashed the commits and updated the descriptions.