Provided by: perl-doc_5.38.2-3.2build2_all 
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('0o377'); # from octal
$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('01.3267p-4'); # ditto
$x = Math::BigFloat->from_oct('0o1.3267p-4'); # ditto
$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
$y = $x->as_float(); # return as a Math::BigFloat
$y = $x->as_rat(); # return as a Math::BigRat
# 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
$x->fparts(); # numerator and denominator
$x->numerator(); # numerator
$x->denominator(); # denominator
# 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->bfstr(); # string in fractional 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. Anything that is accepted by Perl as a literal numeric constant should be accepted
by this module.
• Leading and trailing whitespace is ignored.
• Leading zeros are ignored, except for floating point numbers with a binary exponent,
in which case the number is interpreted as an octal floating point number. For
example, "01.4p+0" gives 1.5, "00.4p+0" gives 0.5, but "0.4p+0" gives a NaN. And while
"0377" gives 255, "0377p0" gives 255.
• If the string has a "0x" or "0X" prefix, it is interpreted as a hexadecimal number.
• If the string has a "0o" or "0O" prefix, it is interpreted as an octal number. A
floating point literal with a "0" prefix is also interpreted as an octal number.
• If the string has a "0b" or "0B" prefix, it is interpreted as a binary number.
• Underline characters are allowed in the same way as they are allowed in literal
numerical constants.
• If the string can not be interpreted, NaN is returned.
• For hexadecimal, octal, and binary floating point numbers, the exponent must be
separated from the significand (mantissa) by the letter "p" or "P", not "e" or "E" as
with decimal numbers.
Some examples of valid string input
Input string Resulting value
123 123
1.23e2 123
12300e-2 123
67_538_754 67538754
-4_5_6.7_8_9e+0_1_0 -4567890000000
0x13a 314
0x13ap0 314
0x1.3ap+8 314
0x0.00013ap+24 314
0x13a000p-12 314
0o472 314
0o1.164p+8 314
0o0.0001164p+20 314
0o1164000p-10 314
0472 472 Note!
01.164p+8 314
00.0001164p+20 314
01164000p-10 314
0b100111010 314
0b1.0011101p+8 314
0b0.00010011101p+12 314
0b100111010000p-3 314
0x1.921fb5p+1 3.14159262180328369140625e+0
0o1.2677025p1 2.71828174591064453125
01.2677025p1 2.71828174591064453125
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
NUMERIC LITERALS
After "use Math::BigFloat ':constant'" all numeric literals in the given scope are
converted to "Math::BigFloat" objects. This conversion happens at compile time.
For example,
perl -MMath::BigFloat=:constant -le 'print 2e-150'
prints the exact value of 2e-150. Note that without conversion of constants the expression
2e-150 is calculated using Perl scalars, which leads to an inaccuracte result.
Note that strings are not affected, so that
use Math::BigFloat qw/:constant/;
$y = "1234567890123456789012345678901234567890"
+ "123456789123456789";
does not give you what you expect. You need an explicit Math::BigFloat->new() around at
least one of the operands. You should also quote large constants to prevent loss of
precision:
use Math::BigFloat;
$x = Math::BigFloat->new("1234567889123456789123456789123456789");
Without the quotes Perl converts the large number to a floating point constant at compile
time, and then converts the result to a Math::BigFloat object at runtime, which results in
an inaccurate result.
Hexadecimal, octal, and binary floating point literals
Perl (and this module) accepts hexadecimal, octal, and binary floating point literals, but
use them with care with Perl versions before v5.32.0, because some versions of Perl
silently give the wrong result. Below are some examples of different ways to write the
number decimal 314.
Hexadecimal floating point literals:
0x1.3ap+8 0X1.3AP+8
0x1.3ap8 0X1.3AP8
0x13a0p-4 0X13A0P-4
Octal floating point literals (with "0" prefix):
01.164p+8 01.164P+8
01.164p8 01.164P8
011640p-4 011640P-4
Octal floating point literals (with "0o" prefix) (requires v5.34.0):
0o1.164p+8 0O1.164P+8
0o1.164p8 0O1.164P8
0o11640p-4 0O11640P-4
Binary floating point literals:
0b1.0011101p+8 0B1.0011101P+8
0b1.0011101p8 0B1.0011101P8
0b10011101000p-2 0B10011101000P-2
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.
See Math::BigInt for more details 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:
• GitHub
<https://github.com/pjacklam/p5-Math-BigInt>
• RT: CPAN's request tracker
<https://rt.cpan.org/Dist/Display.html?Name=Math-BigInt>
• MetaCPAN
<https://metacpan.org/release/Math-BigInt>
• CPAN Testers Matrix
<http://matrix.cpantesters.org/?dist=Math-BigInt>
• CPAN Ratings
<https://cpanratings.perl.org/dist/Math-BigInt>
• The Bignum mailing list
• Post to mailing list
"bignum at lists.scsys.co.uk"
• View mailing list
<http://lists.scsys.co.uk/pipermail/bignum/>
• 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::BigInt and Math::BigInt as well as the backends Math::BigInt::FastCalc,
Math::BigInt::GMP, and Math::BigInt::Pari.
The pragmas bignum, bigint and bigrat.
AUTHORS
• Mark Biggar, overloaded interface by Ilya Zakharevich, 1996-2001.
• Completely rewritten by Tels <http://bloodgate.com> in 2001-2008.
• Florian Ragwitz <flora@cpan.org>, 2010.
• Peter John Acklam <pjacklam@gmail.com>, 2011-.