浮点数高精度计算
- bcadd — 2个任意精度数字的加法计算
- bccomp — 比较两个任意精度的数字
- bcdiv — 2个任意精度的数字除法计算
- bcmod — 对一个任意精度数字取模
- bcmul — 2个任意精度数字乘法计算
- bcpow — 任意精度数字的乘方
- bcpowmod — Raise an arbitrary precision number to another, reduced by a specified modulus
- bcscale — 设置所有bc数学函数的默认小数点保留位数
- bcsqrt — 任意精度数字的二次方根
- bcsub — 2个任意精度数字的减法
/**
* Add two arbitrary precision numbers
* @link https://php.net/manual/en/function.bcadd.php
* @param string $left_operand <p>
* The left operand, as a string.
* </p>
* @param string $right_operand <p>
* The right operand, as a string.
* </p>
* @param int $scale [optional] <p>
* This optional parameter is used to set the number of digits after the
* decimal place in the result. If omitted, it will default to the scale
* set globally with the {@link bcscale()} function, or fallback to 0 if
* this has not been set.
* </p>
* @return string The sum of the two operands, as a string.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bcadd ($left_operand, $right_operand, $scale = 0) {}
/**
* Subtract one arbitrary precision number from another
* @link https://php.net/manual/en/function.bcsub.php
* @param string $left_operand <p>
* The left operand, as a string.
* </p>
* @param string $right_operand <p>
* The right operand, as a string.
* </p>
* @param int $scale [optional] <p>
* This optional parameter is used to set the number of digits after the
* decimal place in the result. If omitted, it will default to the scale
* set globally with the {@link bcscale()} function, or fallback to 0 if
* this has not been set.
* </p>
* @return string The result of the subtraction, as a string.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bcsub ($left_operand, $right_operand, $scale = 0) {}
/**
* Multiply two arbitrary precision numbers
* @link https://php.net/manual/en/function.bcmul.php
* @param string $left_operand <p>
* The left operand, as a string.
* </p>
* @param string $right_operand <p>
* The right operand, as a string.
* </p>
* @param int $scale [optional] <p>
* This optional parameter is used to set the number of digits after the
* decimal place in the result. If omitted, it will default to the scale
* set globally with the {@link bcscale()} function, or fallback to 0 if
* this has not been set.
* </p>
* @return string the result as a string.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bcmul ($left_operand, $right_operand, $scale = 0) {}
/**
* Divide two arbitrary precision numbers
* @link https://php.net/manual/en/function.bcdiv.php
* @param string $dividend <p>
* The dividend, as a string.
* </p>
* @param string $divisor <p>
* The divisor, as a string.
* </p>
* @param int $scale [optional] <p>
* This optional parameter is used to set the number of digits after the
* decimal place in the result. If omitted, it will default to the scale
* set globally with the {@link bcscale()} function, or fallback to 0 if
* this has not been set.
* </p>
* @return string|null the result of the division as a string, or <b>NULL</b> if
* <i>divisor</i> is 0.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bcdiv ($dividend, $divisor, $scale = 0) {}
/**
* Get modulus of an arbitrary precision number
* @link https://php.net/manual/en/function.bcmod.php
* @param string $dividend <p>
* The dividend, as a string.
* </p>
* @param string $divisor <p>
* The divisor, as a string.
* </p>
* @param int $scale [optional] <p>
* This optional parameter is used to set the number of digits after the
* decimal place in the result. If omitted, it will default to the scale
* set globally with the {@link bcscale()} function, or fallback to 0 if
* this has not been set.
* </p>
* @return string|null the modulus as a string, or <b>NULL</b> if
* <i>divisor</i> is 0.
* @since 4.0
* @since 5.0
* @since 7.0
* @since 7.2.0 scale param added, dividend/divisor no longer truncated
*/
function bcmod ($dividend, $divisor, $scale = 0) {}
/**
* Raise an arbitrary precision number to another
* @link https://php.net/manual/en/function.bcpow.php
* @param string $base <p>
* The base, as a string.
* </p>
* @param string $exponent <p>
* The exponent, as a string. If the exponent is non-integral, it is truncated.
* The valid range of the exponent is platform specific, but is at least
* -2147483648 to 2147483647.
* </p>
* @param int $scale [optional] <p>
* This optional parameter is used to set the number of digits after the
* decimal place in the result. If omitted, it will default to the scale
* set globally with the {@link bcscale()} function, or fallback to 0 if
* this has not been set.
* </p>
* @return string the result as a string.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bcpow ($base, $exponent, $scale = 0) {}
/**
* Get the square root of an arbitrary precision number
* @link https://php.net/manual/en/function.bcsqrt.php
* @param string $operand <p>
* The operand, as a string.
* </p>
* @param int $scale [optional]
* @return string the square root as a string, or <b>NULL</b> if
* <i>operand</i> is negative.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bcsqrt ($operand, $scale = null) {}
/**
* Set default scale parameter for all bc math functions
* @link https://php.net/manual/en/function.bcscale.php
* @param int $scale <p>
* The scale factor.
* </p>
* @return bool <b>TRUE</b> on success or <b>FALSE</b> on failure.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bcscale ($scale) {}
/**
* Compare two arbitrary precision numbers
* @link https://php.net/manual/en/function.bccomp.php
* @param string $left_operand <p>
* The left operand, as a string.
* </p>
* @param string $right_operand <p>
* The right operand, as a string.
* </p>
* @param int $scale [optional] <p>
* The optional <i>scale</i> parameter is used to set the
* number of digits after the decimal place which will be used in the
* comparison.
* </p>
* @return int 0 if the two operands are equal, 1 if the
* <i>left_operand</i> is larger than the
* <i>right_operand</i>, -1 otherwise.
* @since 4.0
* @since 5.0
* @since 7.0
*/
function bccomp ($left_operand, $right_operand, $scale = 0) {}
/**
* Raise an arbitrary precision number to another, reduced by a specified modulus
* @link https://php.net/manual/en/function.bcpowmod.php
* @param string $base <p>
* The base, as an integral string (i.e. the scale has to be zero).
* </p>
* @param string $exponent <p>
* The exponent, as an non-negative, integral string (i.e. the scale has to be
* zero).
* </p>
* @param string $modulus <p>
* The modulus, as an integral string (i.e. the scale has to be zero).
* </p>
* @param int $scale [optional] <p>
* This optional parameter is used to set the number of digits after the
* decimal place in the result. If omitted, it will default to the scale
* set globally with the {@link bcscale()} function, or fallback to 0 if
* this has not been set.
* </p>
* @return string|null the result as a string, or <b>NULL</b> if <i>modulus</i>
* is 0 or <i>exponent</i> is negative.
* @since 5.0
* @since 7.0
*/
function bcpowmod ($base, $exponent, $modulus, $scale = 0) {}
常用数值处理方案
舍去法取整(向下取整)
echo floor(5.1);
//输出：5
echo floor(8.8);
//输出：8进一法取整(向上取整)
echo ceil(5.1);
//输出：6
echo ceil(8.8);
//输出：9普通四舍五入法
echo round(5.1);
//输出：5
echo round(8.8);
//输出：9
//保留两位小数并且进行四舍五入
echo round(5.123, 2);
//输出：5.12
echo round(8.888, 2);
//输出：8.89
//保留两位小数并且不进行四舍五入
echo substr(round(5.12345, 3), 0, -1);
//输出：5.12
echo substr(round(8.88888, 3), 0, -1);
//输出：8.88银行家舍入法
四舍六入五考虑，五后非空就进一，五后为空看奇偶，五前为偶应舍去，五前为奇要进一。
保留两位小数，例：
- 1.2849 = 1.28 -> 四舍
- 1.2866 = 1.29 -> 六入
- 1.2851 = 1.29 -> 五后非空就进一
- 1.2850 = 1.28 -> 五后为空看奇偶，五前为偶应舍去
- 1.2750 = 1.28 -> 五后为空看奇偶，五前为奇要进一
实现代码如下：
echo round(1.2849, 2, PHP_ROUND_HALF_EVEN);
//输出：1.28
echo round(1.2866, 2, PHP_ROUND_HALF_EVEN);
//输出：1.29
echo round(1.2851, 2, PHP_ROUND_HALF_EVEN);
//输出：1.29
echo round(1.2850, 2, PHP_ROUND_HALF_EVEN);
//输出：1.28
echo round(1.2750, 2, PHP_ROUND_HALF_EVEN);
//输出：1.28
数值格式化(千位分组)
应用于金额的展示，比如我们经常会看的银行卡余额。
echo number_format('10000.98', 2, '.', ',');
//输出：10,000.98
echo number_format('340888999', 2, '.', ',');
//输出：340,888,999.00扩展
MySQL 浮点型字段
在 MySQL 中，创建表字段时也有浮点数类型。
浮点数类型包括单精度浮点数（float）和双精度浮点数（double）。
同理，不建议使用浮点数类型！！！
浮点数存在误差，当我们使用精度敏感的数据时，应该使用定点数（decimal）进行存储。
