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Slightly improve base85 performance for 64-bit systems

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Summary:
Ref T13130. I wasn't able make this much better, but it looks like this is about ~20% faster on my system.

This kind of thing is somewhat difficult to micro-optimize because XHProf tends to over-estimate the cost of function calls. In XHProf, this looks much much faster than the old version (~100% faster) but the actual cost of `bin/conduit call --method differential.getrawdiff` hasn't improved that much. Still, it seems consistently faster across multiple runs.

Test Plan:
  - Pulled binary diffs over Conduit with `bin/conduit call --method differential.getrawdiff`.
  - Verified that they are byte-for-byte identical with the pre-change diffs, and look like they're ~20% faster.
  - Profiled the differences and saw a far more dramatic improvement, but I believe XHProf is exaggerating the effect of this change because it tends to overestimate function call cost.
  - Ran unit tests (from D19407), got byte-for-byte identical output under both 32bit and 64bit mode.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13130

Differential Revision: https://secure.phabricator.com/D19408
This commit is contained in:
epriestley 2018-04-25 07:57:54 -07:00
parent bcab677a7a
commit a604548101
1 changed files with 61 additions and 36 deletions
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71
src/parser/ArcanistBundle.php
View file

@ -800,13 +800,16 @@ final class ArcanistBundle extends Phobject {
}
$input = gzcompress($data);
$is_64bit = (PHP_INT_SIZE >= 8);
} else {
switch ($mode) {
case '32bit':
$input = $data;
$is_64bit = false;
break;
case '64bit':
$input = $data;
$is_64bit = true;
break;
default:
throw new Exception(
@ -818,25 +821,6 @@ final class ArcanistBundle extends Phobject {
// See emit_binary_diff_body() in diff.c for git's implementation.
$buf = '';
$lines = str_split($input, 52);
foreach ($lines as $line) {
$len = strlen($line);
// The first character encodes the line length.
if ($len <= 26) {
$buf .= chr($len + ord('A') - 1);
} else {
$buf .= chr($len - 26 + ord('a') - 1);
}
$buf .= self::encodeBase85($line);
$buf .= $eol;
}
return $buf;
}
private static function encodeBase85($data) {
// This is implemented awkwardly in order to closely mirror git's
// implementation in base85.c
@ -864,6 +848,9 @@ final class ArcanistBundle extends Phobject {
// (Since PHP overflows integer operations into floats, we don't need much
// additional casting.)
// On 64 bit systems, we skip all this fanfare and just use integers. This
// is significantly faster.
static $map = array(
'0',
'1',
@ -952,29 +939,67 @@ final class ArcanistBundle extends Phobject {
'~',
);
$len_map = array();
for ($ii = 0; $ii <= 52; $ii++) {
if ($ii <= 26) {
$len_map[$ii] = chr($ii + ord('A') - 1);
} else {
$len_map[$ii] = chr($ii - 26 + ord('a') - 1);
}
}
$buf = '';
$lines = str_split($input, 52);
$final = (count($lines) - 1);
foreach ($lines as $idx => $line) {
if ($idx === $final) {
$len = strlen($line);
} else {
$len = 52;
}
// The first character encodes the line length.
$buf .= $len_map[$len];
$pos = 0;
$bytes = strlen($data);
while ($bytes) {
while ($len) {
$accum = 0;
for ($count = 24; $count >= 0; $count -= 8) {
$val = ord($data[$pos++]);
$val = ord($line[$pos++]);
$val = $val * (1 << $count);
$accum = $accum + $val;
if (--$bytes == 0) {
if (--$len == 0) {
break;
}
}
$slice = '';
// If we're in 64bit mode, we can just use integers. Otherwise, we
// need to use floating point math to avoid overflows.
if ($is_64bit) {
for ($count = 4; $count >= 0; $count--) {
$val = $accum % 85;
$accum = $accum / 85;
$slice .= $map[$val];
}
} else {
for ($count = 4; $count >= 0; $count--) {
$val = (int)fmod($accum, 85.0);
$accum = floor($accum / 85.0);
$slice .= $map[$val];
}
}
$buf .= strrev($slice);
}
$buf .= $eol;
}
return $buf;
}