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random: Optimize Randomizer::getBytes() #15228

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merged 1 commit into from
Aug 5, 2024
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random: Optimize Randomizer::getBytes() #15228

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4 changes: 2 additions & 2 deletions ext/random/php_random.h
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Original file line number Diff line number Diff line change
Expand Up @@ -85,8 +85,8 @@ typedef struct _php_random_status_state_user {
} php_random_status_state_user;

typedef struct _php_random_result {
const uint64_t result;
const size_t size;
uint64_t result;
size_t size;
} php_random_result;

typedef struct _php_random_algo {
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39 changes: 37 additions & 2 deletions ext/random/randomizer.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@

#include "Zend/zend_enum.h"
#include "Zend/zend_exceptions.h"
#include "zend_portability.h"

static inline void randomizer_common_init(php_random_randomizer *randomizer, zend_object *engine_object) {
if (engine_object->ce->type == ZEND_INTERNAL_CLASS) {
Expand Down Expand Up @@ -292,14 +293,48 @@ PHP_METHOD(Random_Randomizer, getBytes)
size_t length = (size_t)user_length;
retval = zend_string_alloc(length, 0);

php_random_result result;
while (total_size + 8 <= length) {
result = engine.algo->generate(engine.state);
if (EG(exception)) {
zend_string_free(retval);
RETURN_THROWS();
}

/* If the result is not 64 bits, we can't use the fast path and
* we don't attempt to use it in the future, because we don't
* expect engines to change their output size.
*
* While it would be possible to always memcpy() the entire output,
* using result.size as the length that would result in much worse
* assembly, because it will actually emit a call to memcpy()
* instead of just storing the 64 bit value at a memory offset.
*/
if (result.size != 8) {
goto non_64;
}

#ifdef WORDS_BIGENDIAN
uint64_t swapped = ZEND_BYTES_SWAP64(result.result);
memcpy(ZSTR_VAL(retval) + total_size, &swapped, 8);
#else
memcpy(ZSTR_VAL(retval) + total_size, &result.result, 8);
#endif
total_size += 8;
}

Comment on lines +315 to +325
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I am confused, is it intended for this to run the second while loop again? Or should it skip it to return the value directly?

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It will enter the second loop if the requested length is not a multiple of 8 to handle the remaining 1-7 bytes.

while (total_size < length) {
php_random_result result = engine.algo->generate(engine.state);
result = engine.algo->generate(engine.state);
if (EG(exception)) {
zend_string_free(retval);
RETURN_THROWS();
}

non_64:

for (size_t i = 0; i < result.size; i++) {
ZSTR_VAL(retval)[total_size++] = (result.result >> (i * 8)) & 0xff;
ZSTR_VAL(retval)[total_size++] = result.result & 0xff;
result.result >>= 8;
if (total_size >= length) {
break;
}
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