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Math::BigFloat(3pm)    Perl Programmers Reference Guide    Math::BigFloat(3pm)




NAME

       Math::BigFloat - Arbitrary size floating point math package


SYNOPSIS

         use Math::BigFloat;

         # Configuration methods (may be used as class methods and instance methods)

         Math::BigFloat->accuracy();     # get class accuracy
         Math::BigFloat->accuracy($n);   # set class accuracy
         Math::BigFloat->precision();    # get class precision
         Math::BigFloat->precision($n);  # set class precision
         Math::BigFloat->round_mode();   # get class rounding mode
         Math::BigFloat->round_mode($m); # set global round mode, must be one of
                                         # 'even', 'odd', '+inf', '-inf', 'zero',
                                         # 'trunc', or 'common'
         Math::BigFloat->config("lib");  # name of backend math library

         # Constructor methods (when the class methods below are used as instance
         # methods, the value is assigned the invocand)

         $x = Math::BigFloat->new($str);               # defaults to 0
         $x = Math::BigFloat->new('0x123');            # from hexadecimal
         $x = Math::BigFloat->new('0b101');            # from binary
         $x = Math::BigFloat->from_hex('0xc.afep+3');  # from hex
         $x = Math::BigFloat->from_hex('cafe');        # ditto
         $x = Math::BigFloat->from_oct('1.3267p-4');   # from octal
         $x = Math::BigFloat->from_oct('0377');        # ditto
         $x = Math::BigFloat->from_bin('0b1.1001p-4'); # from binary
         $x = Math::BigFloat->from_bin('0101');        # ditto
         $x = Math::BigFloat->from_ieee754($b, "binary64");  # from IEEE-754 bytes
         $x = Math::BigFloat->bzero();                 # create a +0
         $x = Math::BigFloat->bone();                  # create a +1
         $x = Math::BigFloat->bone('-');               # create a -1
         $x = Math::BigFloat->binf();                  # create a +inf
         $x = Math::BigFloat->binf('-');               # create a -inf
         $x = Math::BigFloat->bnan();                  # create a Not-A-Number
         $x = Math::BigFloat->bpi();                   # returns pi

         $y = $x->copy();        # make a copy (unlike $y = $x)
         $y = $x->as_int();      # return as BigInt

         # Boolean methods (these don't modify the invocand)

         $x->is_zero();          # if $x is 0
         $x->is_one();           # if $x is +1
         $x->is_one("+");        # ditto
         $x->is_one("-");        # if $x is -1
         $x->is_inf();           # if $x is +inf or -inf
         $x->is_inf("+");        # if $x is +inf
         $x->is_inf("-");        # if $x is -inf
         $x->is_nan();           # if $x is NaN

         $x->is_positive();      # if $x > 0
         $x->is_pos();           # ditto
         $x->is_negative();      # if $x < 0
         $x->is_neg();           # ditto

         $x->is_odd();           # if $x is odd
         $x->is_even();          # if $x is even
         $x->is_int();           # if $x is an integer

         # Comparison methods

         $x->bcmp($y);           # compare numbers (undef, < 0, == 0, > 0)
         $x->bacmp($y);          # compare absolutely (undef, < 0, == 0, > 0)
         $x->beq($y);            # true if and only if $x == $y
         $x->bne($y);            # true if and only if $x != $y
         $x->blt($y);            # true if and only if $x < $y
         $x->ble($y);            # true if and only if $x <= $y
         $x->bgt($y);            # true if and only if $x > $y
         $x->bge($y);            # true if and only if $x >= $y

         # Arithmetic methods

         $x->bneg();             # negation
         $x->babs();             # absolute value
         $x->bsgn();             # sign function (-1, 0, 1, or NaN)
         $x->bnorm();            # normalize (no-op)
         $x->binc();             # increment $x by 1
         $x->bdec();             # decrement $x by 1
         $x->badd($y);           # addition (add $y to $x)
         $x->bsub($y);           # subtraction (subtract $y from $x)
         $x->bmul($y);           # multiplication (multiply $x by $y)
         $x->bmuladd($y,$z);     # $x = $x * $y + $z
         $x->bdiv($y);           # division (floored), set $x to quotient
                                 # return (quo,rem) or quo if scalar
         $x->btdiv($y);          # division (truncated), set $x to quotient
                                 # return (quo,rem) or quo if scalar
         $x->bmod($y);           # modulus (x % y)
         $x->btmod($y);          # modulus (truncated)
         $x->bmodinv($mod);      # modular multiplicative inverse
         $x->bmodpow($y,$mod);   # modular exponentiation (($x ** $y) % $mod)
         $x->bpow($y);           # power of arguments (x ** y)
         $x->blog();             # logarithm of $x to base e (Euler's number)
         $x->blog($base);        # logarithm of $x to base $base (e.g., base 2)
         $x->bexp();             # calculate e ** $x where e is Euler's number
         $x->bnok($y);           # x over y (binomial coefficient n over k)
         $x->bsin();             # sine
         $x->bcos();             # cosine
         $x->batan();            # inverse tangent
         $x->batan2($y);         # two-argument inverse tangent
         $x->bsqrt();            # calculate square root
         $x->broot($y);          # $y'th root of $x (e.g. $y == 3 => cubic root)
         $x->bfac();             # factorial of $x (1*2*3*4*..$x)

         $x->blsft($n);          # left shift $n places in base 2
         $x->blsft($n,$b);       # left shift $n places in base $b
                                 # returns (quo,rem) or quo (scalar context)
         $x->brsft($n);          # right shift $n places in base 2
         $x->brsft($n,$b);       # right shift $n places in base $b
                                 # returns (quo,rem) or quo (scalar context)

         # Bitwise methods

         $x->band($y);           # bitwise and
         $x->bior($y);           # bitwise inclusive or
         $x->bxor($y);           # bitwise exclusive or
         $x->bnot();             # bitwise not (two's complement)

         # Rounding methods
         $x->round($A,$P,$mode); # round to accuracy or precision using
                                 # rounding mode $mode
         $x->bround($n);         # accuracy: preserve $n digits
         $x->bfround($n);        # $n > 0: round to $nth digit left of dec. point
                                 # $n < 0: round to $nth digit right of dec. point
         $x->bfloor();           # round towards minus infinity
         $x->bceil();            # round towards plus infinity
         $x->bint();             # round towards zero

         # Other mathematical methods

         $x->bgcd($y);            # greatest common divisor
         $x->blcm($y);            # least common multiple

         # Object property methods (do not modify the invocand)

         $x->sign();              # the sign, either +, - or NaN
         $x->digit($n);           # the nth digit, counting from the right
         $x->digit(-$n);          # the nth digit, counting from the left
         $x->length();            # return number of digits in number
         ($xl,$f) = $x->length(); # length of number and length of fraction
                                  # part, latter is always 0 digits long
                                  # for Math::BigInt objects
         $x->mantissa();          # return (signed) mantissa as BigInt
         $x->exponent();          # return exponent as BigInt
         $x->parts();             # return (mantissa,exponent) as BigInt
         $x->sparts();            # mantissa and exponent (as integers)
         $x->nparts();            # mantissa and exponent (normalised)
         $x->eparts();            # mantissa and exponent (engineering notation)
         $x->dparts();            # integer and fraction part

         # Conversion methods (do not modify the invocand)

         $x->bstr();         # decimal notation, possibly zero padded
         $x->bsstr();        # string in scientific notation with integers
         $x->bnstr();        # string in normalized notation
         $x->bestr();        # string in engineering notation
         $x->bdstr();        # string in decimal notation
         $x->as_hex();       # as signed hexadecimal string with prefixed 0x
         $x->as_bin();       # as signed binary string with prefixed 0b
         $x->as_oct();       # as signed octal string with prefixed 0
         $x->to_ieee754($format); # to bytes encoded according to IEEE 754-2008

         # Other conversion methods

         $x->numify();           # return as scalar (might overflow or underflow)


DESCRIPTION

       Math::BigFloat provides support for arbitrary precision floating point.
       Overloading is also provided for Perl operators.

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

         $x = Math::BigFloat -> new('12_3.456_789_123_456_789E-2');

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

   Input
       Input values to these routines may be any scalar number or string that
       looks like a number and represents a floating point number.

       o   Leading and trailing whitespace is ignored.

       o   Leading and trailing zeros are ignored.

       o   If the string has a "0x" prefix, it is interpreted as a hexadecimal
           number.

       o   If the string has a "0b" prefix, it is interpreted as a binary
           number.

       o   For hexadecimal and binary numbers, the exponent must be separated
           from the significand (mantissa) by the letter "p" or "P", not "e"
           or "E" as with decimal numbers.

       o   One underline is allowed between any two digits, including
           hexadecimal and binary digits.

       o   If the string can not be interpreted, NaN is returned.

       Octal numbers are typically prefixed by "0", but since leading zeros
       are stripped, these methods can not automatically recognize octal
       numbers, so use the constructor from_oct() to interpret octal strings.

       Some examples of valid string input

           Input string                Resulting value
           123                         123
           1.23e2                      123
           12300e-2                    123
           0xcafe                      51966
           0b1101                      13
           67_538_754                  67538754
           -4_5_6.7_8_9e+0_1_0         -4567890000000
           0x1.921fb5p+1               3.14159262180328369140625e+0
           0b1.1001p-4                 9.765625e-2

   Output
       Output values are usually Math::BigFloat objects.

       Boolean operators "is_zero()", "is_one()", "is_inf()", etc. return true
       or false.

       Comparison operators "bcmp()" and "bacmp()") return -1, 0, 1, or undef.


METHODS

       Math::BigFloat supports all methods that Math::BigInt supports, except
       it calculates non-integer results when possible. Please see
       Math::BigInt for a full description of each method. Below are just the
       most important differences:

   Configuration methods
       accuracy()
               $x->accuracy(5);           # local for $x
               CLASS->accuracy(5);        # global for all members of CLASS
                                          # Note: This also applies to new()!

               $A = $x->accuracy();       # read out accuracy that affects $x
               $A = CLASS->accuracy();    # read out global accuracy

           Set or get the global or local accuracy, aka how many significant
           digits the results have. If you set a global accuracy, then this
           also applies to new()!

           Warning! The accuracy sticks, e.g. once you created a number under
           the influence of "CLASS->accuracy($A)", all results from math
           operations with that number will also be rounded.

           In most cases, you should probably round the results explicitly
           using one of "round()" in Math::BigInt, "bround()" in Math::BigInt
           or "bfround()" in Math::BigInt or by passing the desired accuracy
           to the math operation as additional parameter:

               my $x = Math::BigInt->new(30000);
               my $y = Math::BigInt->new(7);
               print scalar $x->copy()->bdiv($y, 2);           # print 4300
               print scalar $x->copy()->bdiv($y)->bround(2);   # print 4300

       precision()
               $x->precision(-2);        # local for $x, round at the second
                                         # digit right of the dot
               $x->precision(2);         # ditto, round at the second digit
                                         # left of the dot

               CLASS->precision(5);      # Global for all members of CLASS
                                         # This also applies to new()!
               CLASS->precision(-5);     # ditto

               $P = CLASS->precision();  # read out global precision
               $P = $x->precision();     # read out precision that affects $x

           Note: You probably want to use "accuracy()" instead. With
           "accuracy()" you set the number of digits each result should have,
           with "precision()" you set the place where to round!

   Constructor methods
       from_hex()
               $x -> from_hex("0x1.921fb54442d18p+1");
               $x = Math::BigFloat -> from_hex("0x1.921fb54442d18p+1");

           Interpret input as a hexadecimal string.A prefix ("0x", "x",
           ignoring case) is optional. A single underscore character ("_") may
           be placed between any two digits. If the input is invalid, a NaN is
           returned. The exponent is in base 2 using decimal digits.

           If called as an instance method, the value is assigned to the
           invocand.

       from_oct()
               $x -> from_oct("1.3267p-4");
               $x = Math::BigFloat -> from_oct("1.3267p-4");

           Interpret input as an octal string. A single underscore character
           ("_") may be placed between any two digits. If the input is
           invalid, a NaN is returned. The exponent is in base 2 using decimal
           digits.

           If called as an instance method, the value is assigned to the
           invocand.

       from_bin()
               $x -> from_bin("0b1.1001p-4");
               $x = Math::BigFloat -> from_bin("0b1.1001p-4");

           Interpret input as a hexadecimal string. A prefix ("0b" or "b",
           ignoring case) is optional. A single underscore character ("_") may
           be placed between any two digits. If the input is invalid, a NaN is
           returned. The exponent is in base 2 using decimal digits.

           If called as an instance method, the value is assigned to the
           invocand.

       from_ieee754()
           Interpret the input as a value encoded as described in
           IEEE754-2008.  The input can be given as a byte string, hex string
           or binary string. The input is assumed to be in big-endian byte-
           order.

                   # both $dbl and $mbf are 3.141592...
                   $bytes = "\x40\x09\x21\xfb\x54\x44\x2d\x18";
                   $dbl = unpack "d>", $bytes;
                   $mbf = Math::BigFloat -> from_ieee754($bytes, "binary64");

       bpi()
               print Math::BigFloat->bpi(100), "\n";

           Calculate PI to N digits (including the 3 before the dot). The
           result is rounded according to the current rounding mode, which
           defaults to "even".

           This method was added in v1.87 of Math::BigInt (June 2007).

   Arithmetic methods
       bmuladd()
               $x->bmuladd($y,$z);

           Multiply $x by $y, and then add $z to the result.

           This method was added in v1.87 of Math::BigInt (June 2007).

       bdiv()
               $q = $x->bdiv($y);
               ($q, $r) = $x->bdiv($y);

           In scalar context, divides $x by $y and returns the result to the
           given or default accuracy/precision. In list context, does floored
           division (F-division), returning an integer $q and a remainder $r
           so that $x = $q * $y + $r. The remainer (modulo) is equal to what
           is returned by "$x->bmod($y)".

       bmod()
               $x->bmod($y);

           Returns $x modulo $y. When $x is finite, and $y is finite and non-
           zero, the result is identical to the remainder after floored
           division (F-division). If, in addition, both $x and $y are
           integers, the result is identical to the result from Perl's %
           operator.

       bexp()
               $x->bexp($accuracy);            # calculate e ** X

           Calculates the expression "e ** $x" where "e" is Euler's number.

           This method was added in v1.82 of Math::BigInt (April 2007).

       bnok()
               $x->bnok($y);   # x over y (binomial coefficient n over k)

           Calculates the binomial coefficient n over k, also called the
           "choose" function. The result is equivalent to:

               ( n )      n!
               | - |  = -------
               ( k )    k!(n-k)!

           This method was added in v1.84 of Math::BigInt (April 2007).

       bsin()
               my $x = Math::BigFloat->new(1);
               print $x->bsin(100), "\n";

           Calculate the sinus of $x, modifying $x in place.

           This method was added in v1.87 of Math::BigInt (June 2007).

       bcos()
               my $x = Math::BigFloat->new(1);
               print $x->bcos(100), "\n";

           Calculate the cosinus of $x, modifying $x in place.

           This method was added in v1.87 of Math::BigInt (June 2007).

       batan()
               my $x = Math::BigFloat->new(1);
               print $x->batan(100), "\n";

           Calculate the arcus tanges of $x, modifying $x in place. See also
           "batan2()".

           This method was added in v1.87 of Math::BigInt (June 2007).

       batan2()
               my $y = Math::BigFloat->new(2);
               my $x = Math::BigFloat->new(3);
               print $y->batan2($x), "\n";

           Calculate the arcus tanges of $y divided by $x, modifying $y in
           place.  See also "batan()".

           This method was added in v1.87 of Math::BigInt (June 2007).

       as_float()
           This method is called when Math::BigFloat encounters an object it
           doesn't know how to handle. For instance, assume $x is a
           Math::BigFloat, or subclass thereof, and $y is defined, but not a
           Math::BigFloat, or subclass thereof. If you do

               $x -> badd($y);

           $y needs to be converted into an object that $x can deal with. This
           is done by first checking if $y is something that $x might be
           upgraded to. If that is the case, no further attempts are made. The
           next is to see if $y supports the method "as_float()". The method
           "as_float()" is expected to return either an object that has the
           same class as $x, a subclass thereof, or a string that
           "ref($x)->new()" can parse to create an object.

           In Math::BigFloat, "as_float()" has the same effect as "copy()".

       to_ieee754()
           Encodes the invocand as a byte string in the given format as
           specified in IEEE 754-2008. Note that the encoded value is the
           nearest possible representation of the value. This value might not
           be exactly the same as the value in the invocand.

               # $x = 3.1415926535897932385
               $x = Math::BigFloat -> bpi(30);

               $b = $x -> to_ieee754("binary64");  # encode as 8 bytes
               $h = unpack "H*", $b;               # "400921fb54442d18"

               # 3.141592653589793115997963...
               $y = Math::BigFloat -> from_ieee754($h, "binary64");

           All binary formats in IEEE 754-2008 are accepted. For convenience,
           som aliases are recognized: "half" for "binary16", "single" for
           "binary32", "double" for "binary64", "quadruple" for "binary128",
           "octuple" for "binary256", and "sexdecuple" for "binary512".

           See also <https://en.wikipedia.org/wiki/IEEE_754>.

   ACCURACY AND PRECISION
       See also: Rounding.

       Math::BigFloat supports both precision (rounding to a certain place
       before or after the dot) and accuracy (rounding to a certain number of
       digits). For a full documentation, examples and tips on these topics
       please see the large section about rounding in Math::BigInt.

       Since things like sqrt(2) or "1 / 3" must presented with a limited
       accuracy lest a operation consumes all resources, each operation
       produces no more than the requested number of digits.

       If there is no global precision or accuracy set, and the operation in
       question was not called with a requested precision or accuracy, and the
       input $x has no accuracy or precision set, then a fallback parameter
       will be used. For historical reasons, it is called "div_scale" and can
       be accessed via:

           $d = Math::BigFloat->div_scale();       # query
           Math::BigFloat->div_scale($n);          # set to $n digits

       The default value for "div_scale" is 40.

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

           $x = Math::BigFloat->new(2);
           Math::BigFloat->accuracy(5);              # 5 digits max
           $y = $x->copy()->bdiv(3);                 # gives 0.66667
           $y = $x->copy()->bdiv(3,6);               # gives 0.666667
           $y = $x->copy()->bdiv(3,6,undef,'odd');   # gives 0.666667
           Math::BigFloat->round_mode('zero');
           $y = $x->copy()->bdiv(3,6);               # will also give 0.666667

       Note that "Math::BigFloat->accuracy()" and
       "Math::BigFloat->precision()" set the global variables, and thus any
       newly created number will be subject to the global rounding
       immediately. This means that in the examples above, the 3 as argument
       to "bdiv()" will also get an accuracy of 5.

       It is less confusing to either calculate the result fully, and
       afterwards round it explicitly, or use the additional parameters to the
       math functions like so:

           use Math::BigFloat;
           $x = Math::BigFloat->new(2);
           $y = $x->copy()->bdiv(3);
           print $y->bround(5),"\n";               # gives 0.66667

           or

           use Math::BigFloat;
           $x = Math::BigFloat->new(2);
           $y = $x->copy()->bdiv(3,5);             # gives 0.66667
           print "$y\n";

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

       bfround ( -$scale )
           Rounds to the $scale'th place right from the '.', counting from the
           dot.

       bfround ( 0 )
           Rounds to an integer.

       bround  ( +$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 '.'

       bround  ( -$scale ) and bround ( 0 )
           These are effectively no-ops.

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

       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:

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

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

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


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

           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:

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

       You can change this by using:

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

       Note: General purpose packages should not be explicit about the library
       to use; let the script author decide which is best.

       Note: The keyword 'lib' will warn when the requested library could not
       be loaded. To suppress the warning use 'try' instead:

           use Math::BigFloat try => 'GMP';

       If your script works with huge numbers and Calc is too slow for them,
       you can also for the loading of one of these libraries and if none of
       them can be used, the code will die:

           use Math::BigFloat only => 'GMP,Pari';

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

           use Math::BigFloat lib => 'Foo,Math::BigInt::Bar';

       See the respective low-level library 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:

           use Math::BigInt lib => 'GMP';
           use Math::BigFloat;

       you can roll it all into one line:

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

       It is also possible to just require Math::BigFloat:

           require Math::BigFloat;

       This will load the necessary things (like BigInt) when they are needed,
       and automatically.

       See Math::BigInt for more details than you ever wanted to know about
       using a different low-level library.

   Using Math::BigInt::Lite
       For backwards compatibility reasons it is still possible to request a
       different storage class for use with Math::BigFloat:

           use Math::BigFloat with => 'Math::BigInt::Lite';

       However, this request is ignored, as the current code now uses the low-
       level math library for directly storing the number parts.


EXPORTS

       "Math::BigFloat" exports nothing by default, but can export the "bpi()"
       method:

           use Math::BigFloat qw/bpi/;

           print bpi(10), "\n";


CAVEATS

       Do not try to be clever to insert some operations in between switching
       libraries:

           require Math::BigFloat;
           my $matter = Math::BigFloat->bone() + 4;    # load BigInt and Calc
           Math::BigFloat->import( lib => 'Pari' );    # load Pari, too
           my $anti_matter = Math::BigFloat->bone()+4; # now use Pari

       This will create objects with numbers stored in two different backend
       libraries, and VERY BAD THINGS will happen when you use these together:

           my $flash_and_bang = $matter + $anti_matter;    # Don't do this!

       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.

       brsft()
           The following will probably not print what you expect:

               my $c = Math::BigFloat->new('3.14159');
               print $c->brsft(3,10),"\n";     # prints 0.00314153.1415

           It prints both quotient and remainder, since print calls "brsft()"
           in list context. Also, "$c->brsft()" will modify $c, so be careful.
           You probably want to use

               print scalar $c->copy()->brsft(3,10),"\n";
               # or if you really want to modify $c
               print scalar $c->brsft(3,10),"\n";

           instead.

       Modifying and =
           Beware of:

               $x = Math::BigFloat->new(5);
               $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 (except
           overloaded math operators), and vice versa. See Math::BigInt for
           details and how to avoid that.

       precision() vs. accuracy()
           A common pitfall is to use "precision()" when you want to round a
           result to a certain number of digits:

               use Math::BigFloat;

               Math::BigFloat->precision(4);           # does not do what you
                                                       # think it does
               my $x = Math::BigFloat->new(12345);     # rounds $x to "12000"!
               print "$x\n";                           # print "12000"
               my $y = Math::BigFloat->new(3);         # rounds $y to "0"!
               print "$y\n";                           # print "0"
               $z = $x / $y;                           # 12000 / 0 => NaN!
               print "$z\n";
               print $z->precision(),"\n";             # 4

           Replacing "precision()" with "accuracy()" is probably not what you
           want, either:

               use Math::BigFloat;

               Math::BigFloat->accuracy(4);          # enables global rounding:
               my $x = Math::BigFloat->new(123456);  # rounded immediately
                                                     #   to "12350"
               print "$x\n";                         # print "123500"
               my $y = Math::BigFloat->new(3);       # rounded to "3
               print "$y\n";                         # print "3"
               print $z = $x->copy()->bdiv($y),"\n"; # 41170
               print $z->accuracy(),"\n";            # 4

           What you want to use instead is:

               use Math::BigFloat;

               my $x = Math::BigFloat->new(123456);    # no rounding
               print "$x\n";                           # print "123456"
               my $y = Math::BigFloat->new(3);         # no rounding
               print "$y\n";                           # print "3"
               print $z = $x->copy()->bdiv($y,4),"\n"; # 41150
               print $z->accuracy(),"\n";              # undef

           In addition to computing what you expected, the last example also
           does not "taint" the result with an accuracy or precision setting,
           which would influence any further operation.


BUGS

       Please report any bugs or feature requests to "bug-math-bigint at
       rt.cpan.org", or through the web interface at
       <https://rt.cpan.org/Ticket/Create.html?Queue=Math-BigInt> (requires
       login).  We will be notified, and then you'll automatically be notified
       of progress on your bug as I make changes.


SUPPORT

       You can find documentation for this module with the perldoc command.

           perldoc Math::BigFloat

       You can also look for information at:

       o   RT: CPAN's request tracker

           <https://rt.cpan.org/Public/Dist/Display.html?Name=Math-BigInt>

       o   AnnoCPAN: Annotated CPAN documentation

           <http://annocpan.org/dist/Math-BigInt>

       o   CPAN Ratings

           <https://cpanratings.perl.org/dist/Math-BigInt>

       o   MetaCPAN

           <https://metacpan.org/release/Math-BigInt>

       o   CPAN Testers Matrix

           <http://matrix.cpantesters.org/?dist=Math-BigInt>

       o   The Bignum mailing list

           o   Post to mailing list

               "bignum at lists.scsys.co.uk"

           o   View mailing list

               <http://lists.scsys.co.uk/pipermail/bignum/>

           o   Subscribe/Unsubscribe

               <http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/bignum>


LICENSE

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


SEE ALSO

       Math::BigFloat and Math::BigInt(3) as well as the backends
       Math::BigInt::FastCalc(3), Math::BigInt::GMP(3), and 
       Math::BigInt::Pari(3).

       The pragmas bignum(3), bigint(3) and bigrat(3) also might be of
       interest because they solve the autoupgrading/downgrading issue, at
       least partly.


AUTHORS

       o   Mark Biggar, overloaded interface by Ilya Zakharevich, 1996-2001.

       o   Completely rewritten by Tels <http://bloodgate.com> in 2001-2008.

       o   Florian Ragwitz <flora@cpan.org>, 2010.

       o   Peter John Acklam <pjacklam@online.no>, 2011-.



perl v5.34.0                      2020-06-14               Math::BigFloat(3pm)

perl 5.34.0 - Generated Thu Mar 3 05:37:23 CST 2022
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