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random: Optimize data flow for the generate function of native engines (#13043)

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Instead of returning the generated `uint64_t` and providing the size (i.e. the
number of bytes of the generated value) out-of-band via the
`last_generated_size` member of the `php_random_status` struct, the `generate`
function is now expected to return a new `php_random_result` struct containing
both the `size` and the `result`.

This has two benefits, one for the developer:

It's no longer possible to forget setting `last_generated_size` to the correct
value, because it now happens at the time of returning from the function.

and the other benefit is for performance:

The `php_random_result` struct will be returned as a register pair, thus the
`size` will be directly available without reloading it from main memory.

Checking a simplified version of `php_random_range64()` on Compiler Explorer
(“Godbolt”) with clang 17 shows a single change in the resulting assembly
showcasing the improvement (https://godbolt.org/z/G4WjdYxqx):

    - add     rbp, qword ptr [r14]
    + add     rbp, rdx

Empirical testing confirms a measurable performance increase for the
`Randomizer::getBytes()` method:

    <?php
    $e = new Random\Engine\Xoshiro256StarStar(0);
    $r = new Random\Randomizer($e);

    var_dump(strlen($r->getBytes(100000000)));

goes from 250ms (before the change) to 220ms (after the change). While
generating 100 MB of random data certainly is not the most common use case, it
confirms the theoretical improvement in practice.
This commit is contained in:
Tim Düsterhus 2024-01-09 19:04:29 +01:00 • committed by GitHub
parent d778c24aa2
commit 162e1dce98
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GPG key ID: 4AEE18F83AFDEB23
10 changed files with 82 additions and 64 deletions
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27
ext/random/randomizer.c
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@ -101,9 +101,9 @@ PHP_METHOD(Random_Randomizer, nextFloat)
result = 0;
total_size = 0;
do {
uint64_t r = randomizer->algo->generate(randomizer->status);
result = result | (r << (total_size * 8));
total_size += randomizer->status->last_generated_size;
php_random_result r = randomizer->algo->generate(randomizer->status);
result = result | (r.result << (total_size * 8));
total_size += r.size;
if (EG(exception)) {
RETURN_THROWS();
}
@ -208,20 +208,19 @@ PHP_METHOD(Random_Randomizer, getFloat)
PHP_METHOD(Random_Randomizer, nextInt)
{
php_random_randomizer *randomizer = Z_RANDOM_RANDOMIZER_P(ZEND_THIS);
uint64_t result;
ZEND_PARSE_PARAMETERS_NONE();
result = randomizer->algo->generate(randomizer->status);
php_random_result result = randomizer->algo->generate(randomizer->status);
if (EG(exception)) {
RETURN_THROWS();
}
if (randomizer->status->last_generated_size > sizeof(zend_long)) {
if (result.size > sizeof(zend_long)) {
zend_throw_exception(random_ce_Random_RandomException, "Generated value exceeds size of int", 0);
RETURN_THROWS();
}
RETURN_LONG((zend_long) (result >> 1));
RETURN_LONG((zend_long) (result.result >> 1));
}
/* }}} */
@ -246,7 +245,7 @@ PHP_METHOD(Random_Randomizer, getInt)
randomizer->algo->range == php_random_algo_mt19937.range
&& ((php_random_status_state_mt19937 *) randomizer->status->state)->mode != MT_RAND_MT19937
)) {
uint64_t r = php_random_algo_mt19937.generate(randomizer->status) >> 1;
uint64_t r = php_random_algo_mt19937.generate(randomizer->status).result >> 1;
/* This is an inlined version of the RAND_RANGE_BADSCALING macro that does not invoke UB when encountering
* (max - min) > ZEND_LONG_MAX.
@ -286,13 +285,13 @@ PHP_METHOD(Random_Randomizer, getBytes)
retval = zend_string_alloc(length, 0);
while (total_size < length) {
uint64_t result = randomizer->algo->generate(randomizer->status);
php_random_result result = randomizer->algo->generate(randomizer->status);
if (EG(exception)) {
zend_string_free(retval);
RETURN_THROWS();
}
for (size_t i = 0; i < randomizer->status->last_generated_size; i++) {
ZSTR_VAL(retval)[total_size++] = (result >> (i * 8)) & 0xff;
for (size_t i = 0; i < result.size; i++) {
ZSTR_VAL(retval)[total_size++] = (result.result >> (i * 8)) & 0xff;
if (total_size >= length) {
break;
}
@ -425,14 +424,14 @@ PHP_METHOD(Random_Randomizer, getBytesFromString)
int failures = 0;
while (total_size < length) {
uint64_t result = randomizer->algo->generate(randomizer->status);
php_random_result result = randomizer->algo->generate(randomizer->status);
if (EG(exception)) {
zend_string_free(retval);
RETURN_THROWS();
}
for (size_t i = 0; i < randomizer->status->last_generated_size; i++) {
uint64_t offset = (result >> (i * 8)) & mask;
for (size_t i = 0; i < result.size; i++) {
uint64_t offset = (result.result >> (i * 8)) & mask;
if (offset > max_offset) {
if (++failures > PHP_RANDOM_RANGE_ATTEMPTS) {