gmp_init

Here's a way to parse a decimal (eg 3.25) into an integer and exponent:<?if (preg_match("/^[0-9]+\.[0-9]+$/",$input)){      //Input is a base-10 decimal. Multiply as necessary to remove the decimal     //point. Convert that to a gmp_resource, then decrement the exponent      //to compensate.     $pieces=explode(".", $input);     //Split at the d.p.     $input="$pieces[0]$pieces[1]";  //Remove the decimal point.     $input=ltrim($input,'0');         //Remove any leading zeros, or gmp_init will parse the number as octal.     if ($input==''){    //Deal with "0.0" which would otherwise be ''.          $input=0;      }      $integer=gmp_init($input);         $ns_exponent=-strlen($pieces[1]);       //exponent = (-)  the number of characters after the decimal point.}?>

Unless the base is 16, gpm_init will fail if the string begins with "0b". > php -r '$v = gmp_init("b83", 17); print("$v\n");'Resource id #4> php -r '$v = gmp_init("0b83", 17); print("$v\n");'[nothing prints]In may case, where I am explicitly specifying the base, the solution is to apply ltrim first:> php -r '$v = gmp_init(ltrim("0b83", "0"), 17); print("$v\n");'Resource id #4

I discovered that the gmp functions use [0-9a-f] up to base 16, but [0-9A-Za-z] (i.e. upper case first) from bases 17 to 62. This differs from most of the base-62 implementations I've found that tend to use lower case first.

Note: Leading zeros will make gmp_init parse this as octal.Thus gmp_init(010) becomes 8.  $a=010;              //8$b="010" + 0;     //10$c=gmp_strval(gmp_init(010));    //8$d=gmp_strval(gmp_init("010")); //8This behaviour is inconsistent: either $d should equal $b, or$b should equal $a.

Missing from the documentation: gmp_init() return false in case it failed to parse $num<?phpvar_dump(gmp_init(""));// returns "bool(false)" and not a GMP object as hinted by the documentation, it also triggers a Warning "PHP Warning:  gmp_init(): Unable to convert variable to GMP - string is not an integer in php shell code on line 1"?>

gmp_* functions don't accept strings with a leading '+':<?phpecho gmp_strval(gmp_init('+42'));      #0echo gmp_strval(gmp_add('42', '+42')); #42echo bcadd('+42', '+42');              #84?>

If you call a gmp_* function directly with an interger as parameter, this integer MUST NOT be 0:for($i=-1;$i<=1;$i++) {  echo gmp_strval(gmp_add(2,gmp_mul(1,$i))) . ' ';  }The result is 1 0 3 (wrong)In this case you have to use gmp_init():for($i=-1;$i<=1;$i++) {  echo gmp_strval(gmp_add(2,gmp_mul(1,gmp_init($i)))) . ' ';  }The result is 1 2 3 (right)Happy number crunching! :-)