The constants below are always available as part of the PHP core.
M_PI
(float )
3.14159265358979323846
).
M_E
(float )
e
(2.7182818284590452354
).
M_LOG2E
(float )
log2(e)
(1.4426950408889634074
).
M_LOG10E
(float )
log10(e)
(0.43429448190325182765
).
M_LN2
(float )
ln(2)
(0.69314718055994530942
).
M_LN10
(float )
ln(10)
(2.30258509299404568402
).
M_PI_2
(float )
π/2
(1.57079632679489661923
).
M_PI_4
(float )
π/4
(0.78539816339744830962
).
M_1_PI
(float )
1/π
(0.31830988618379067154
).
M_2_PI
(float )
2/π
(0.63661977236758134308
).
M_SQRTPI
(float )
sqrt(π)
(1.77245385090551602729
).
M_2_SQRTPI
(float )
2/sqrt(π)
(1.12837916709551257390
).
M_SQRT2
(float )
sqrt(2)
(1.41421356237309504880
).
M_SQRT3
(float )
sqrt(3)
(1.73205080756887729352
).
M_SQRT1_2
(float )
1/sqrt(2)
(0.70710678118654752440
).
M_LNPI
(float )
ln(π)
(1.14472988584940017414
).
M_EULER
(float )
0.57721566490153286061
).
Note: As of PHP 8.4.0, it is recommended to use the RoundingMode enum instead.
PHP_ROUND_HALF_UP
(int )
PHP_ROUND_HALF_DOWN
(int )
PHP_ROUND_HALF_EVEN
(int )
PHP_ROUND_HALF_ODD
(int )
I just learnt of INF today and found out that it can be used in comparisons:
echo 5000 < INF ? 'yes' : 'no'; // outputs 'yes'
echo INF < INF ? 'yes' : 'no'; // outputs 'no'
echo INF <= INF ? 'yes' : 'no'; // outputs 'yes'
echo INF == INF ? 'yes' : 'no'; // outputs 'yes'
You can also take its negative:
echo -INF < -5000 ? 'yes' : 'no'; // outputs 'yes'
Division by INF is allowed:
echo 1/INF; // outputs '0'
There are also the predefined PHP_INT_MAX and PHP_INT_SIZE constants, that describe the range of possible integer values.
Although INF can be used for comparison against normal numbers and as a directed number, and behaves as reciprocal of zero, it is not like limit INF tends to infinity. These operations do not work:
<?php
var_dump(INF / INF); // float(NAN)
var_dump(INF - INF); // float(NAN)
?>
However, it works with arc-tangent:
<?php
var_dump(atan(INF) / M_PI); // float(0.5)
var_dump(atan2(INF, INF) / M_PI); // float(0.25)
var_dump(atan2(1, INF) / M_PI); // float(0)
?>
From PHP 7.2.0, the PHP_FLOAT_* constants are provided to describe the properties of floating point numbers that can be stored; PHP_FLOAT_MAX, for example, is analogous to PHP_INT_MAX and represents the largest possible floating-point number.