bccomp()

(PHP 4, PHP 5, PHP 7)

比较两个任意精度的数字

说明

bccomp(string $left_operand,string $right_operand[,int $scale= int]): int

把$right_operand和$left_operand作比较,并且返回一个整数的结果.

参数

$left_operand: 左边的运算数,是一个字符串.
$right_operand: 右边的运算数,是一个字符串.
$scale: 可选的$scale参数被用作设置指示数字，在使用来作比较的小数点部分.

返回值

如果两个数相等返回0,左边的数$left_operand比较右边的数$right_operand大返回1,否则返回-1.

范例

bccomp() example

<?php
echo bccomp('1', '2') . "\n";   // -1
echo bccomp('1.00001', '1', 3); // 0
echo bccomp('1.00001', '1', 5); // 1
?>

Beware that negative zero does not compare equal to positive zero.

BEWARE! left and right operand is string!! so number in E-notation like 9.012E-6 need to be converted with sprintf('%F') to string

Improvement of functions bcmax() and bcmin() originaly written by frank at booksku dot com
<?php
function bcmax() {
 $args = func_get_args();
 if (count($args)==0) return false;
 $max = $args[0];
 foreach($args as $value) {
  if (bccomp($value, $max)==1) {
   $max = $value;
  }
 }
 return $max;
}
function bcmin() {
 $args = func_get_args();
 if (count($args)==0) return false;
 $min = $args[0];
 foreach($args as $value) {
  if (bccomp($min, $value)==1) {
   $min = $value;
  }
 }
 return $min;
}
?>

Note that the above function defeats the purpose of BCMath functions, for it uses the 'conventional' < operator.
Instead, it should be:
<?php
function my_bccomp_zero($amount, $scale)
{
  if (@$amount{0}=="-")
  {
    return bccomp($amount, '-0.0', $scale);
  }
  else
  {
    return bccomp($amount, '0.0', $scale);
  }
}
?>

I slapped together min() and max() functions using bccomp(). While min() and max() only take an arbitrary number of args (i.e. max(1, 5, 1235, 12934, 66)) bccomp only takes 2.
Note that this doesn't take into account $scale.
<?php
function bcmax() {
 $max = null;
 foreach(func_get_args() as $value) {
  if ($max == null) {
   $max = $value;
  } else if (bccomp($max, $value) < 0) {
   $max = $value;
  }
 }
 return $max;
}
function bcmin() {
 $min = null;
 foreach(func_get_args() as $value) {
  if ($min == null) {
   $min = $value;
  } else if (bccomp($min, $value) > 0) {
   $min = $value;
  }
 }
 return $min;
}
?>

I made this to compare an unlimited size of numbers..
This could be useful for those without the BCMath extension. 
It allows decimals, and option $Scale parameter. If $Scale isn't specified, then it'll automatically adjust to the correct number of decimals to compare.
<?php
function Comp($Num1,$Num2,$Scale=null) {
 // check if they're valid positive numbers, extract the whole numbers and decimals
 if(!preg_match("/^\+?(\d+)(\.\d+)?$/",$Num1,$Tmp1)||
   !preg_match("/^\+?(\d+)(\.\d+)?$/",$Num2,$Tmp2)) return('0');
 // remove leading zeroes from whole numbers
 $Num1=ltrim($Tmp1[1],'0');
 $Num2=ltrim($Tmp2[1],'0');
 // first, we can just check the lengths of the numbers, this can help save processing time
 // if $Num1 is longer than $Num2, return 1.. vice versa with the next step.
 if(strlen($Num1)>strlen($Num2)) return(1);
 else {
  if(strlen($Num1)<strlen($Num2)) return(-1);
  // if the two numbers are of equal length, we check digit-by-digit
  else {
   // remove ending zeroes from decimals and remove point
   $Dec1=isset($Tmp1[2])?rtrim(substr($Tmp1[2],1),'0'):'';
   $Dec2=isset($Tmp2[2])?rtrim(substr($Tmp2[2],1),'0'):'';
   // if the user defined $Scale, then make sure we use that only
   if($Scale!=null) {
    $Dec1=substr($Dec1,0,$Scale);
    $Dec2=substr($Dec2,0,$Scale);
   }
   // calculate the longest length of decimals
   $DLen=max(strlen($Dec1),strlen($Dec2));
   // append the padded decimals onto the end of the whole numbers
   $Num1.=str_pad($Dec1,$DLen,'0');
   $Num2.=str_pad($Dec2,$DLen,'0');
   // check digit-by-digit, if they have a difference, return 1 or -1 (greater/lower than)
   for($i=0;$i<strlen($Num1);$i++) {
    if((int)$Num1{$i}>(int)$Num2{$i}) return(1);
    else
     if((int)$Num1{$i}<(int)$Num2{$i}) return(-1);
   }
   // if the two numbers have no difference (they're the same).. return 0
   return(0);
  }
 }
}
$A="10.50002";
$B="10.50001";
printf(" Comp(%s,%s); // %s\r\n",$A,$B, Comp($A,$B));
printf("BCComp(%s,%s); // %s\r\n",$A,$B,BCComp($A,$B));
/*
  Comp(10.50002,10.50001); // 1
 BCComp(10.50002,10.50001); // 0 (BCComp has a default decimal scale of 0, unless specified)
*/
?>
I tried to make this behave like BCComp..
The only difference being mine will compare the decimals by default.. BCComp won't..
.. unless, of course, you specify the amount of decimals to include in the process.
Enjoy,
Nitrogen.

You can wrap this function with version_compare() to have support for operators and friendlier (boolean) return values.
<?php
function _bccomp($a, $b, $operator = '=')
{
  return version_compare(bccomp($a, $b), 0, $operator);
}
var_dump(_bccomp(5, 3, '>=')); // true
?>
Still works with arbitrary length numbers.

bccomp - doesn't compare by default more then 16 characters
$number = '-4.444444444444444444444444444444444444444444445';
$precision = 16;
var_dump(bccomp(bcadd($number, '0', $precision), bcadd($number, '0', $precision+1)));
//outputs 0 on PHP 5.3
use strcomp

In PHP 7, bccomp($a, $b) is the same as $a <=> $b.