Perl 5 version 8.0 documentation



Math::BigFloat - Arbitrary size floating point math package


  1. use Math::BigFloat;
  2. # Number creation
  3. $x = Math::BigFloat->new($str); # defaults to 0
  4. $nan = Math::BigFloat->bnan(); # create a NotANumber
  5. $zero = Math::BigFloat->bzero(); # create a +0
  6. $inf = Math::BigFloat->binf(); # create a +inf
  7. $inf = Math::BigFloat->binf('-'); # create a -inf
  8. $one = Math::BigFloat->bone(); # create a +1
  9. $one = Math::BigFloat->bone('-'); # create a -1
  10. # Testing
  11. $x->is_zero(); # true if arg is +0
  12. $x->is_nan(); # true if arg is NaN
  13. $x->is_one(); # true if arg is +1
  14. $x->is_one('-'); # true if arg is -1
  15. $x->is_odd(); # true if odd, false for even
  16. $x->is_even(); # true if even, false for odd
  17. $x->is_positive(); # true if >= 0
  18. $x->is_negative(); # true if < 0
  19. $x->is_inf(sign); # true if +inf, or -inf (default is '+')
  20. $x->bcmp($y); # compare numbers (undef,<0,=0,>0)
  21. $x->bacmp($y); # compare absolutely (undef,<0,=0,>0)
  22. $x->sign(); # return the sign, either +,- or NaN
  23. $x->digit($n); # return the nth digit, counting from right
  24. $x->digit(-$n); # return the nth digit, counting from left
  25. # The following all modify their first argument:
  26. # set
  27. $x->bzero(); # set $i to 0
  28. $x->bnan(); # set $i to NaN
  29. $x->bone(); # set $x to +1
  30. $x->bone('-'); # set $x to -1
  31. $x->binf(); # set $x to inf
  32. $x->binf('-'); # set $x to -inf
  33. $x->bneg(); # negation
  34. $x->babs(); # absolute value
  35. $x->bnorm(); # normalize (no-op)
  36. $x->bnot(); # two's complement (bit wise not)
  37. $x->binc(); # increment x by 1
  38. $x->bdec(); # decrement x by 1
  39. $x->badd($y); # addition (add $y to $x)
  40. $x->bsub($y); # subtraction (subtract $y from $x)
  41. $x->bmul($y); # multiplication (multiply $x by $y)
  42. $x->bdiv($y); # divide, set $i to quotient
  43. # return (quo,rem) or quo if scalar
  44. $x->bmod($y); # modulus
  45. $x->bpow($y); # power of arguments (a**b)
  46. $x->blsft($y); # left shift
  47. $x->brsft($y); # right shift
  48. # return (quo,rem) or quo if scalar
  49. $x->blog($base); # logarithm of $x, base defaults to e
  50. # (other bases than e not supported yet)
  51. $x->band($y); # bit-wise and
  52. $x->bior($y); # bit-wise inclusive or
  53. $x->bxor($y); # bit-wise exclusive or
  54. $x->bnot(); # bit-wise not (two's complement)
  55. $x->bsqrt(); # calculate square-root
  56. $x->bfac(); # factorial of $x (1*2*3*4*..$x)
  57. $x->bround($N); # accuracy: preserver $N digits
  58. $x->bfround($N); # precision: round to the $Nth digit
  59. # The following do not modify their arguments:
  60. bgcd(@values); # greatest common divisor
  61. blcm(@values); # lowest common multiplicator
  62. $x->bstr(); # return string
  63. $x->bsstr(); # return string in scientific notation
  64. $x->bfloor(); # return integer less or equal than $x
  65. $x->bceil(); # return integer greater or equal than $x
  66. $x->exponent(); # return exponent as BigInt
  67. $x->mantissa(); # return mantissa as BigInt
  68. $x->parts(); # return (mantissa,exponent) as BigInt
  69. $x->length(); # number of digits (w/o sign and '.')
  70. ($l,$f) = $x->length(); # number of digits, and length of fraction
  71. $x->precision(); # return P of $x (or global, if P of $x undef)
  72. $x->precision($n); # set P of $x to $n
  73. $x->accuracy(); # return A of $x (or global, if A of $x undef)
  74. $x->accuracy($n); # set A $x to $n
  75. Math::BigFloat->precision(); # get/set global P for all BigFloat objects
  76. Math::BigFloat->accuracy(); # get/set global A for all BigFloat objects


All operators (inlcuding basic math operations) are overloaded if you declare your big floating point numbers as

  1. $i = new Math::BigFloat '12_3.456_789_123_456_789E-2';

Operations with overloaded operators preserve the arguments, which is exactly what you expect.

Canonical notation

Input to these routines are either BigFloat objects, or strings of the following four forms:

  • /^[+-]\d+$/

  • /^[+-]\d+\.\d*$/

  • /^[+-]\d+E[+-]?\d+$/

  • /^[+-]\d*\.\d+E[+-]?\d+$/

all with optional leading and trailing zeros and/or spaces. Additonally, numbers are allowed to have an underscore between any two digits.

Empty strings as well as other illegal numbers results in 'NaN'.

bnorm() on a BigFloat object is now effectively a no-op, since the numbers are always stored in normalized form. On a string, it creates a BigFloat object.


Output values are BigFloat objects (normalized), except for bstr() and bsstr().

The string output will always have leading and trailing zeros stripped and drop a plus sign. bstr() will give you always the form with a decimal point, while bsstr() (for scientific) gives you the scientific notation.

  1. Input bstr() bsstr()
  2. '-0' '0' '0E1'
  3. ' -123 123 123' '-123123123' '-123123123E0'
  4. '00.0123' '0.0123' '123E-4'
  5. '123.45E-2' '1.2345' '12345E-4'
  6. '10E+3' '10000' '1E4'

Some routines (is_odd() , is_even() , is_zero() , is_one() , is_nan() ) return true or false, while others (bcmp() , bacmp() ) return either undef, <0, 0 or >0 and are suited for sort.

Actual math is done by using BigInts to represent the mantissa and exponent. The sign /^[+-]$/ is stored separately. The string 'NaN' is used to represent the result when input arguments are not numbers, as well as the result of dividing by zero.

mantissa() , exponent() and parts()

mantissa() and exponent() return the said parts of the BigFloat as BigInts such that:

  1. $m = $x->mantissa();
  2. $e = $x->exponent();
  3. $y = $m * ( 10 ** $e );
  4. print "ok\n" if $x == $y;

($m,$e) = $x->parts(); is just a shortcut giving you both of them.

A zero is represented and returned as 0E1 , not 0E0 (after Knuth).

Currently the mantissa is reduced as much as possible, favouring higher exponents over lower ones (e.g. returning 1e7 instead of 10e6 or 10000000e0). This might change in the future, so do not depend on it.

Accuracy vs. Precision

See also: Rounding.

Math::BigFloat supports both precision and accuracy. For a full documentation, examples and tips on these topics please see the large section in Math::BigInt.

Since things like sqrt(2) or 1/3 must presented with a limited precision lest a operation consumes all resources, each operation produces no more than Math::BigFloat::precision() digits.

In case the result of one operation has more precision than specified, it is rounded. The rounding mode taken is either the default mode, or the one supplied to the operation after the scale:

  1. $x = Math::BigFloat->new(2);
  2. Math::BigFloat::precision(5); # 5 digits max
  3. $y = $x->copy()->bdiv(3); # will give 0.66666
  4. $y = $x->copy()->bdiv(3,6); # will give 0.666666
  5. $y = $x->copy()->bdiv(3,6,'odd'); # will give 0.666667
  6. Math::BigFloat::round_mode('zero');
  7. $y = $x->copy()->bdiv(3,6); # will give 0.666666


  • ffround ( +$scale )

    Rounds to the $scale'th place left from the '.', counting from the dot. The first digit is numbered 1.

  • ffround ( -$scale )

    Rounds to the $scale'th place right from the '.', counting from the dot.

  • ffround ( 0 )

    Rounds to an integer.

  • fround ( +$scale )

    Preserves accuracy to $scale digits from the left (aka significant digits) and pads the rest with zeros. If the number is between 1 and -1, the significant digits count from the first non-zero after the '.'

  • fround ( -$scale ) and fround ( 0 )

    These are effetively no-ops.

All rounding functions take as a second parameter a rounding mode from one of the following: 'even', 'odd', '+inf', '-inf', 'zero' or 'trunc'.

The default rounding mode is 'even'. By using Math::BigFloat::round_mode($round_mode); you can get and set the default mode for subsequent rounding. The usage of $Math::BigFloat::$round_mode is no longer supported. The second parameter to the round functions then overrides the default temporarily.

The as_number() function returns a BigInt from a Math::BigFloat. It uses 'trunc' as rounding mode to make it equivalent to:

  1. $x = 2.5;
  2. $y = int($x) + 2;

You can override this by passing the desired rounding mode as parameter to as_number() :

  1. $x = Math::BigFloat->new(2.5);
  2. $y = $x->as_number('odd'); # $y = 3


  1. # not ready yet

Autocreating constants

After use Math::BigFloat ':constant' all the floating point constants in the given scope are converted to Math::BigFloat . This conversion happens at compile time.

In particular

  1. perl -MMath::BigFloat=:constant -e 'print 2E-100,"\n"'

prints the value of 2E-100 . Note that without conversion of constants the expression 2E-100 will be calculated as normal floating point number.

Please note that ':constant' does not affect integer constants, nor binary nor hexadecimal constants. Use bignum or Math::BigInt to get this to work.

Math library

Math with the numbers is done (by default) by a module called Math::BigInt::Calc. This is equivalent to saying:

  1. use Math::BigFloat lib => 'Calc';

You can change this by using:

  1. use Math::BigFloat lib => 'BitVect';

The following would first try to find Math::BigInt::Foo, then Math::BigInt::Bar, and when this also fails, revert to Math::BigInt::Calc:

  1. use Math::BigFloat lib => 'Foo,Math::BigInt::Bar'; uses as internal format an array of elements of some decimal base (usually 1e7, but this might be differen for some systems) with the least significant digit first, while uses a bit vector of base 2, most significant bit first. Other modules might use even different means of representing the numbers. See the respective module documentation for further details.

Please note that Math::BigFloat does not use the denoted library itself, but it merely passes the lib argument to Math::BigInt. So, instead of the need to do:

  1. use Math::BigInt lib => 'GMP';
  2. use Math::BigFloat;

you can roll it all into one line:

  1. use Math::BigFloat lib => 'GMP';

Use the lib, Luke! And see Using Math::BigInt::Lite for more details.

Using Math::BigInt::Lite

It is possible to use Math::BigInt::Lite with Math::BigFloat:

  1. # 1
  2. use Math::BigFloat with => 'Math::BigInt::Lite';

There is no need to "use Math::BigInt" or "use Math::BigInt::Lite", but you can combine these if you want. For instance, you may want to use Math::BigInt objects in your main script, too.

  1. # 2
  2. use Math::BigInt;
  3. use Math::BigFloat with => 'Math::BigInt::Lite';

Of course, you can combine this with the lib parameter.

  1. # 3
  2. use Math::BigFloat with => 'Math::BigInt::Lite', lib => 'GMP,Pari';

If you want to use Math::BigInt's, too, simple add a Math::BigInt before:

  1. # 4
  2. use Math::BigInt;
  3. use Math::BigFloat with => 'Math::BigInt::Lite', lib => 'GMP,Pari';

Notice that the module with the last lib will "win" and thus it's lib will be used if the lib is available:

  1. # 5
  2. use Math::BigInt lib => 'Bar,Baz';
  3. use Math::BigFloat with => 'Math::BigInt::Lite', lib => 'Foo';

That would try to load Foo, Bar, Baz and Calc (in that order). Or in other words, Math::BigFloat will try to retain previously loaded libs when you don't specify it one.

Actually, the lib loading order would be "Bar,Baz,Calc", and then "Foo,Bar,Baz,Calc", but independend of which lib exists, the result is the same as trying the latter load alone, except for the fact that Bar or Baz might be loaded needlessly in an intermidiate step

The old way still works though:

  1. # 6
  2. use Math::BigInt lib => 'Bar,Baz';
  3. use Math::BigFloat;

But examples #3 and #4 are recommended for usage.


  • The following does not work yet:

    1. $m = $x->mantissa();
    2. $e = $x->exponent();
    3. $y = $m * ( 10 ** $e );
    4. print "ok\n" if $x == $y;
  • There is no fmod() function yet.


  • stringify, bstr()

    Both stringify and bstr() now drop the leading '+'. The old code would return '+1.23', the new returns '1.23'. See the documentation in Math::BigInt for reasoning and details.

  • bdiv

    The following will probably not do what you expect:

    1. print $c->bdiv(123.456),"\n";

    It prints both quotient and reminder since print works in list context. Also, bdiv() will modify $c, so be carefull. You probably want to use

    1. print $c / 123.456,"\n";
    2. print scalar $c->bdiv(123.456),"\n"; # or if you want to modify $c


  • Modifying and =

    Beware of:

    1. $x = Math::BigFloat->new(5);
    2. $y = $x;

    It will not do what you think, e.g. making a copy of $x. Instead it just makes a second reference to the same object and stores it in $y. Thus anything that modifies $x will modify $y, and vice versa.

    1. $x->bmul(2);
    2. print "$x, $y\n"; # prints '10, 10'

    If you want a true copy of $x, use:

    1. $y = $x->copy();

    See also the documentation in overload regarding = .

  • bpow

    bpow() now modifies the first argument, unlike the old code which left it alone and only returned the result. This is to be consistent with badd() etc. The first will modify $x, the second one won't:

    1. print bpow($x,$i),"\n"; # modify $x
    2. print $x->bpow($i),"\n"; # ditto
    3. print $x ** $i,"\n"; # leave $x alone


This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.


Mark Biggar, overloaded interface by Ilya Zakharevich. Completely rewritten by Tels in 2001.