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Fix GH-12143: Optimize round #12268

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Fix GH-12143: Optimize round #12268

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a8b422c
optimized round() processing
SakiTakamachi Sep 22, 2023
0faa198
optimized round() processing
SakiTakamachi Sep 22, 2023
bf3daaf
rename test
SakiTakamachi Sep 22, 2023
7d6b939
use UNEXPECTED
SakiTakamachi Dec 9, 2023
5bfcbe5
Unify variable names such as f1 to "exponent"
SakiTakamachi Jan 29, 2024
1b41af8
Compatible with new modes
SakiTakamachi Jan 29, 2024
b9d4f3c
Changes the CPU rounding mode only during a specific process.
SakiTakamachi Jan 31, 2024
1a36254
[skip ci] NEWS/UPGRADING
SakiTakamachi Jan 31, 2024
e7e4725
use zend_always_inline
SakiTakamachi Feb 1, 2024
0c64e30
Remove unnecessary "const"
SakiTakamachi Feb 1, 2024
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1 change: 1 addition & 0 deletions NEWS
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Original file line number Diff line number Diff line change
Expand Up @@ -149,6 +149,7 @@ Standard:
the precision is not lost. (Marc Bennewitz)
. Add support for 4 new rounding modes to the round() function. (Jorg Sowa)
. debug_zval_dump() now indicates whether an array is packed. (Max Semenik)
. Fix GH-12143 (Optimize round). (SakiTakamachi)

XML:
. Added XML_OPTION_PARSE_HUGE parser option. (nielsdos)
Expand Down
5 changes: 5 additions & 0 deletions UPGRADING
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Expand Up @@ -343,6 +343,11 @@ PDO_SQLITE:

RFC: https://wiki.php.net/rfc/new_rounding_modes_to_round_function
. debug_zval_dump() now indicates whether an array is packed.
. Fixed a bug caused by "pre-rounding" of the round() function. Previously, using
"pre-rounding" to treat a value like 0.285 (actually 0.28499999999999998) as a
decimal number and round it to 0.29. However, "pre-rounding" incorrectly rounds
certain numbers, so this fix removes "pre-rounding" and changes the way numbers
are compared, so that the values ​​are correctly rounded as decimal numbers.

========================================
6. New Functions
Expand Down
174 changes: 66 additions & 108 deletions ext/standard/math.c
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Expand Up @@ -27,53 +27,10 @@
#include <float.h>
#include <math.h>
#include <stdlib.h>
#include <fenv.h>

#include "basic_functions.h"

/* {{{ php_intlog10abs
Returns floor(log10(fabs(val))), uses fast binary search */
static inline int php_intlog10abs(double value) {
value = fabs(value);

if (value < 1e-8 || value > 1e22) {
return (int)floor(log10(value));
} else {
/* Do a binary search with 5 steps */
int result = 15;
static const double values[] = {
1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1, 1e0, 1e1, 1e2,
1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11, 1e12, 1e13,
1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22};

if (value < values[result]) {
result -= 8;
} else {
result += 8;
}
if (value < values[result]) {
result -= 4;
} else {
result += 4;
}
if (value < values[result]) {
result -= 2;
} else {
result += 2;
}
if (value < values[result]) {
result -= 1;
} else {
result += 1;
}
if (value < values[result]) {
result -= 1;
}
result -= 8;
return result;
}
}
/* }}} */

/* {{{ php_intpow10
Returns pow(10.0, (double)power), uses fast lookup table for exact powers */
static inline double php_intpow10(int power) {
Expand All @@ -90,22 +47,30 @@ static inline double php_intpow10(int power) {
}
/* }}} */

/* {{{ php_round_helper
Actually performs the rounding of a value to integer in a certain mode */
static inline double php_round_helper(double value, int mode) {
double integral, fractional;
static zend_always_inline double php_round_get_basic_edge_case(double integral, double exponent, int places)
{
return (places > 0)
? fabs((integral + copysign(0.5, integral)) / exponent)
: fabs((integral + copysign(0.5, integral)) * exponent);
}

/* Split the input value into the integral and fractional part.
*
* Both parts will have the same sign as the input value. We take
* the absolute value of the fractional part (which will not result
* in branches in the assembly) to make the following cases simpler.
*/
fractional = fabs(modf(value, &integral));
static zend_always_inline double php_round_get_zero_edge_case(double integral, double exponent, int places)
{
return (places > 0)
? fabs((integral) / exponent)
: fabs((integral) * exponent);
}

/* {{{ php_round_helper
Actually performs the rounding of a value to integer in a certain mode */
static inline double php_round_helper(double integral, double value, double exponent, int places, int mode) {
double value_abs = fabs(value);
double edge_case;

switch (mode) {
case PHP_ROUND_HALF_UP:
if (fractional >= 0.5) {
edge_case = php_round_get_basic_edge_case(integral, exponent, places);
if (value_abs >= edge_case) {
/* We must increase the magnitude of the integral part
* (rounding up / towards infinity). copysign(1.0, integral)
* will either result in 1.0 or -1.0 depending on the sign
Expand All @@ -120,21 +85,24 @@ static inline double php_round_helper(double value, int mode) {
return integral;

case PHP_ROUND_HALF_DOWN:
if (fractional > 0.5) {
edge_case = php_round_get_basic_edge_case(integral, exponent, places);
if (value_abs > edge_case) {
return integral + copysign(1.0, integral);
}

return integral;

case PHP_ROUND_CEILING:
if (value > 0.0 && fractional > 0.0) {
edge_case = php_round_get_zero_edge_case(integral, exponent, places);
if (value > 0.0 && value_abs > edge_case) {
return integral + 1.0;
}

return integral;

case PHP_ROUND_FLOOR:
if (value < 0.0 && fractional > 0.0) {
edge_case = php_round_get_zero_edge_case(integral, exponent, places);
if (value < 0.0 && value_abs > edge_case) {
return integral - 1.0;
}

Expand All @@ -144,18 +112,18 @@ static inline double php_round_helper(double value, int mode) {
return integral;

case PHP_ROUND_AWAY_FROM_ZERO:
if (fractional > 0.0) {
edge_case = php_round_get_zero_edge_case(integral, exponent, places);
if (value_abs > edge_case) {
return integral + copysign(1.0, integral);
}

return integral;

case PHP_ROUND_HALF_EVEN:
if (fractional > 0.5) {
edge_case = php_round_get_basic_edge_case(integral, exponent, places);
if (value_abs > edge_case) {
return integral + copysign(1.0, integral);
}

if (UNEXPECTED(fractional == 0.5)) {
} else if (UNEXPECTED(value_abs == edge_case)) {
bool even = !fmod(integral, 2.0);

/* If the integral part is not even we can make it even
Expand All @@ -169,11 +137,10 @@ static inline double php_round_helper(double value, int mode) {
return integral;

case PHP_ROUND_HALF_ODD:
if (fractional > 0.5) {
edge_case = php_round_get_basic_edge_case(integral, exponent, places);
if (value_abs > edge_case) {
return integral + copysign(1.0, integral);
}

if (UNEXPECTED(fractional == 0.5)) {
} else if (UNEXPECTED(value_abs == edge_case)) {
bool even = !fmod(integral, 2.0);

if (even) {
Expand All @@ -196,63 +163,55 @@ static inline double php_round_helper(double value, int mode) {
* mode. For the specifics of the algorithm, see http://wiki.php.net/rfc/rounding
*/
PHPAPI double _php_math_round(double value, int places, int mode) {
double f1, f2;
double exponent;
double tmp_value;
int precision_places;
int cpu_round_mode;

if (!zend_finite(value) || value == 0.0) {
return value;
}

places = places < INT_MIN+1 ? INT_MIN+1 : places;
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This is unrelated to this, but possibly something we should adress in a follow-up PR, to emit a warning or throw a ValueError if the provided places argument doesn't make sense

precision_places = 14 - php_intlog10abs(value);

f1 = php_intpow10(abs(places));
exponent = php_intpow10(abs(places));

/* If the decimal precision guaranteed by FP arithmetic is higher than
the requested places BUT is small enough to make sure a non-zero value
is returned, pre-round the result to the precision */
if (precision_places > places && precision_places - 15 < places) {
int64_t use_precision = precision_places < INT_MIN+1 ? INT_MIN+1 : precision_places;

f2 = php_intpow10(abs((int)use_precision));
if (use_precision >= 0) {
tmp_value = value * f2;
} else {
tmp_value = value / f2;
}
/* preround the result (tmp_value will always be something * 1e14,
thus never larger than 1e15 here) */
tmp_value = php_round_helper(tmp_value, mode);

use_precision = places - precision_places;
use_precision = use_precision < INT_MIN+1 ? INT_MIN+1 : use_precision;
/* now correctly move the decimal point */
f2 = php_intpow10(abs((int)use_precision));
/* because places < precision_places */
tmp_value = tmp_value / f2;
/**
* When extracting the integer part, the result may be incorrect as a decimal
* number due to floating point errors.
* e.g.
* 0.285 * 10000000000 => 2849999999.9999995
* floor(0.285 * 10000000000) => 2849999999
*
* Therefore, change the CPU rounding mode to away from 0 only from
* fegetround to fesetround.
* e.g.
* 0.285 * 10000000000 => 2850000000.0
* floor(0.285 * 10000000000) => 2850000000
*/
cpu_round_mode = fegetround();
if (value >= 0.0) {
fesetround(FE_UPWARD);
tmp_value = floor(places > 0 ? value * exponent : value / exponent);
} else {
/* adjust the value */
if (places >= 0) {
tmp_value = value * f1;
} else {
tmp_value = value / f1;
}
/* This value is beyond our precision, so rounding it is pointless */
if (fabs(tmp_value) >= 1e15) {
return value;
}
fesetround(FE_DOWNWARD);
tmp_value = ceil(places > 0 ? value * exponent : value / exponent);
}
fesetround(cpu_round_mode);

/* This value is beyond our precision, so rounding it is pointless */
if (fabs(tmp_value) >= 1e15) {
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By the way, to increase the number of digits that can be processed, you can simply change this to 1e16.

return value;
}

/* round the temp value */
tmp_value = php_round_helper(tmp_value, mode);
tmp_value = php_round_helper(tmp_value, value, exponent, places, mode);

/* see if it makes sense to use simple division to round the value */
if (abs(places) < 23) {
if (places > 0) {
tmp_value = tmp_value / f1;
tmp_value = tmp_value / exponent;
} else {
tmp_value = tmp_value * f1;
tmp_value = tmp_value * exponent;
}
} else {
/* Simple division can't be used since that will cause wrong results.
Expand All @@ -272,7 +231,6 @@ PHPAPI double _php_math_round(double value, int places, int mode) {
tmp_value = value;
}
}

return tmp_value;
}
/* }}} */
Expand Down
74 changes: 60 additions & 14 deletions ext/standard/tests/math/bug24142.phpt
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Expand Up @@ -2,19 +2,65 @@
Bug #24142 (round() problems)
--FILE--
<?php
$v = 0.005;
for ($i = 1; $i < 10; $i++) {
echo "round({$v}, 2) -> ".round($v, 2)."\n";
$v += 0.01;
}
echo "round(0.005, 2)\n";
var_dump(round(0.005, 2));
echo "\n";

echo "round(0.015, 2)\n";
var_dump(round(0.015, 2));
echo "\n";

echo "round(0.025, 2)\n";
var_dump(round(0.025, 2));
echo "\n";

echo "round(0.035, 2)\n";
var_dump(round(0.035, 2));
echo "\n";

echo "round(0.045, 2)\n";
var_dump(round(0.045, 2));
echo "\n";

echo "round(0.055, 2)\n";
var_dump(round(0.055, 2));
echo "\n";

echo "round(0.065, 2)\n";
var_dump(round(0.065, 2));
echo "\n";

echo "round(0.075, 2)\n";
var_dump(round(0.075, 2));
echo "\n";

echo "round(0.085, 2)\n";
var_dump(round(0.085, 2));
?>
--EXPECT--
round(0.005, 2) -> 0.01
round(0.015, 2) -> 0.02
round(0.025, 2) -> 0.03
round(0.035, 2) -> 0.04
round(0.045, 2) -> 0.05
round(0.055, 2) -> 0.06
round(0.065, 2) -> 0.07
round(0.075, 2) -> 0.08
round(0.085, 2) -> 0.09
round(0.005, 2)
float(0.01)

round(0.015, 2)
float(0.02)

round(0.025, 2)
float(0.03)

round(0.035, 2)
float(0.04)

round(0.045, 2)
float(0.05)

round(0.055, 2)
float(0.06)

round(0.065, 2)
float(0.07)

round(0.075, 2)
float(0.08)

round(0.085, 2)
float(0.09)
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