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Reimplement php_round_helper() using modf() #12220

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Merged
merged 6 commits into from
Sep 19, 2023
Merged

Reimplement php_round_helper() using modf() #12220

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afa4dba
Reimplement `php_round_helper()` using `modf()`
TimWolla Sep 15, 2023
a995a2f
Use `ZEND_UNREACHABLE()` in `php_round_helper()`
TimWolla Sep 17, 2023
945f5f9
Reorder branches for PHP_ROUND_HALF_EVEN / PHP_ROUND_HALF_ODD
TimWolla Sep 17, 2023
e5716cb
Separate the HALF_EVEN and HALF_ODD modes into dedicated cases
TimWolla Sep 17, 2023
f3cf180
Add some explanatory comments to php_round_helper()
TimWolla Sep 19, 2023
ff62f61
[ci skip] NEWS / UPGRADING
TimWolla Sep 19, 2023
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49 changes: 32 additions & 17 deletions ext/standard/math.c
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Original file line number Diff line number Diff line change
Expand Up @@ -93,27 +93,42 @@ 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 tmp_value;
double integral, fractional;

if (value >= 0.0) {
tmp_value = floor(value + 0.5);
if ((mode == PHP_ROUND_HALF_DOWN && value == (-0.5 + tmp_value)) ||
(mode == PHP_ROUND_HALF_EVEN && value == (0.5 + 2 * floor(tmp_value/2.0))) ||
(mode == PHP_ROUND_HALF_ODD && value == (0.5 + 2 * floor(tmp_value/2.0) - 1.0)))
{
tmp_value = tmp_value - 1.0;
}
} else {
tmp_value = ceil(value - 0.5);
if ((mode == PHP_ROUND_HALF_DOWN && value == (0.5 + tmp_value)) ||
(mode == PHP_ROUND_HALF_EVEN && value == (-0.5 + 2 * ceil(tmp_value/2.0))) ||
(mode == PHP_ROUND_HALF_ODD && value == (-0.5 + 2 * ceil(tmp_value/2.0) + 1.0)))
{
tmp_value = tmp_value + 1.0;
fractional = fabs(modf(value, &integral));

switch (mode) {
case PHP_ROUND_HALF_UP:
if (fractional >= 0.5) {
return integral + copysign(1.0, integral);
}

return integral;
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clang is able to compile this branchless as per: https://godbolt.org/z/5cb8W1416, which is likely a good thing.


case PHP_ROUND_HALF_DOWN:
if (fractional > 0.5) {
return integral + copysign(1.0, integral);
}

return integral;

case PHP_ROUND_HALF_EVEN:
case PHP_ROUND_HALF_ODD: {
if (fractional == 0.5) {
bool even = !fmod(integral, 2.0);

if ((mode == PHP_ROUND_HALF_EVEN && !even) || (mode == PHP_ROUND_HALF_ODD && even)) {
return integral + copysign(1.0, integral);
}
} else if (fractional > 0.5) {
return integral + copysign(1.0, integral);
}

return integral;
}
}

return tmp_value;
ZEND_ASSERT(0 && "Unknown rounding mode");
}
/* }}} */

Expand Down
27 changes: 27 additions & 0 deletions ext/standard/tests/math/round_gh12143_1.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
--TEST--
GH-12143: Test rounding of 0.49999999999999994.
--FILE--
<?php
foreach ([
0.49999999999999994,
-0.49999999999999994,
] as $number) {
foreach ([
'PHP_ROUND_HALF_UP',
'PHP_ROUND_HALF_DOWN',
'PHP_ROUND_HALF_EVEN',
'PHP_ROUND_HALF_ODD',
] as $mode) {
printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
}
}
?>
--EXPECT--
PHP_ROUND_HALF_UP : +0.49999999999999994 -> +0
PHP_ROUND_HALF_DOWN : +0.49999999999999994 -> +0
PHP_ROUND_HALF_EVEN : +0.49999999999999994 -> +0
PHP_ROUND_HALF_ODD : +0.49999999999999994 -> +0
PHP_ROUND_HALF_UP : -0.49999999999999994 -> -0
PHP_ROUND_HALF_DOWN : -0.49999999999999994 -> -0
PHP_ROUND_HALF_EVEN : -0.49999999999999994 -> -0
PHP_ROUND_HALF_ODD : -0.49999999999999994 -> -0
27 changes: 27 additions & 0 deletions ext/standard/tests/math/round_gh12143_2.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
--TEST--
GH-12143: Test rounding of 0.50000000000000011.
--FILE--
<?php
foreach ([
0.50000000000000011,
-0.50000000000000011,
] as $number) {
foreach ([
'PHP_ROUND_HALF_UP',
'PHP_ROUND_HALF_DOWN',
'PHP_ROUND_HALF_EVEN',
'PHP_ROUND_HALF_ODD',
] as $mode) {
printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
}
}
?>
--EXPECT--
PHP_ROUND_HALF_UP : +0.50000000000000011 -> +1
PHP_ROUND_HALF_DOWN : +0.50000000000000011 -> +1
PHP_ROUND_HALF_EVEN : +0.50000000000000011 -> +1
PHP_ROUND_HALF_ODD : +0.50000000000000011 -> +1
PHP_ROUND_HALF_UP : -0.50000000000000011 -> -1
PHP_ROUND_HALF_DOWN : -0.50000000000000011 -> -1
PHP_ROUND_HALF_EVEN : -0.50000000000000011 -> -1
PHP_ROUND_HALF_ODD : -0.50000000000000011 -> -1
27 changes: 27 additions & 0 deletions ext/standard/tests/math/round_gh12143_3.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
--TEST--
GH-12143: Test rounding of 0.5.
--FILE--
<?php
foreach ([
0.5,
-0.5,
] as $number) {
foreach ([
'PHP_ROUND_HALF_UP',
'PHP_ROUND_HALF_DOWN',
'PHP_ROUND_HALF_EVEN',
'PHP_ROUND_HALF_ODD',
] as $mode) {
printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
}
}
?>
--EXPECT--
PHP_ROUND_HALF_UP : +0.5 -> +1
PHP_ROUND_HALF_DOWN : +0.5 -> +0
PHP_ROUND_HALF_EVEN : +0.5 -> +0
PHP_ROUND_HALF_ODD : +0.5 -> +1
PHP_ROUND_HALF_UP : -0.5 -> -1
PHP_ROUND_HALF_DOWN : -0.5 -> -0
PHP_ROUND_HALF_EVEN : -0.5 -> -0
PHP_ROUND_HALF_ODD : -0.5 -> -1
27 changes: 27 additions & 0 deletions ext/standard/tests/math/round_gh12143_4.phpt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
--TEST--
GH-12143: Test rounding of 1.5.
--FILE--
<?php
foreach ([
1.5,
-1.5,
] as $number) {
foreach ([
'PHP_ROUND_HALF_UP',
'PHP_ROUND_HALF_DOWN',
'PHP_ROUND_HALF_EVEN',
'PHP_ROUND_HALF_ODD',
] as $mode) {
printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
}
}
?>
--EXPECT--
PHP_ROUND_HALF_UP : +1.5 -> +2
PHP_ROUND_HALF_DOWN : +1.5 -> +1
PHP_ROUND_HALF_EVEN : +1.5 -> +2
PHP_ROUND_HALF_ODD : +1.5 -> +1
PHP_ROUND_HALF_UP : -1.5 -> -2
PHP_ROUND_HALF_DOWN : -1.5 -> -1
PHP_ROUND_HALF_EVEN : -1.5 -> -2
PHP_ROUND_HALF_ODD : -1.5 -> -1