See the GMP documentation at http://gmplib.org.
These next 3 functions are demonstrated above:
$rop = Rmpq_init();
Rmpq_set_strl($rop, $str, $base); # 1 < $base < 63
$str = Rmpq_get_str($op, $base); # 1 < $base < 37
The following functions are simply wrappers around a GMP
function of the same name. eg. Rmpq_swap() is a wrapper around
mpq_swap() which is fully documented in the GMP manual at
http://gmplib.org.
"$rop", "$op1", "$op2", etc. are simply Math::GMPq objects -
the return value of Rmpq_init or Rmpq_init_nobless
functions. They are in fact references to GMP structures.
The "$rop" argument(s) contain the result(s) of the calculation
being done, the "$op" argument(s) being the input(s) into that
calculation.
Generally, $rop, $op1, $op2, etc. can be the same perl variable,
though usually they will be distinct perl variables referencing
distinct GMP structures.
Eg. something like Rmpq_add($r1, $r1, $r1),
where $r1 *is* the same reference to the same GMP structure,
would add $r1 to itself and store the result in $r1. Think of it
as $r1 += $r1. Otoh, Rmpq_add($r1, $r2, $r3), where each of the
arguments is a different reference to a different GMP structure
would add $r2 to $r3 and store the result in $r1. Think of it as
$r1 = $r2 + $r3. Mostly, the first argument is the argument that
stores the result and subsequent arguments provide the input values.
Exceptions to this can be found in some of the functions that
actually return a value.
Like I say, see the GMP manual for details. I hope it's
intuitively obvious or quickly becomes so. Also see the test
suite that comes with the distro for some examples of usage.
"$ui" means any integer that will fit into a C 'unsigned long int.
"$si" means any integer that will fit into a C 'signed long int'.
"$double" means any number (not necessarily integer) that will fit
into a C 'double'.
"$NV" is perl's floating point type (run "perl -V:nvtype")
"$bool" means a value (usually a 'signed long int') in which
the only interest is whether it evaluates as true or false.
"$str" simply means a string of symbols that represent a number,
eg "1234567890987654321234567/7".
Valid bases for GMP numbers are 2 to 62 (inclusive).
############
CANONICALIZE
Rmpq_canonicalize($op);
Remove any factors that are common to the numerator and
denominator of $op, and make the denominator positive.
##########
INITIALIZE
Normally, a variable should be initialized once only or at least be
cleared, using `Rmpq_clear', between initializations.
'DESTROY' (which calls 'Rmpq_clear') is automatically called on
blessed objects whenever they go out of scope.
See the section 'MEMORY MANAGEMENT' (above).
$rop = Math::GMPq::new();
$rop = Math::GMPq->new();
$rop = new Math::GMPq();
$rop = Rmpq_init();
$rop = Rmpq_init_nobless();
Initialize $rop and set it to 0/1.
####################
ASSIGNMENT FUNCTIONS
Rmpq_set($rop, $op);
Rmpq_set_z($rop, $z); # $z is a Math::GMPz object
Set $rop to value contained in 2nd arg.
Rmpq_set_ui($rop, $ui1 , $ui2);
Rmpq_set_si($rop, $si , $ui );
Rmpq_set_IV($rop, $iv1 , $iv2);
Set $rop to 2nd arg / 3rd arg.
The 3rd arg should be an unsigned value. That is, the value -2/3
should be assigned as 2nd arg is -2, 3rd arg is 3 ... not 2nd
arg is 2, third arg is -3.
With Rmpq_set_IV, $iv1 and $iv2 must both have their IOK flag set,
or the function will croak. Best to first check IOK_flag($iv), which
will return a non-zero value if and only if the IOK flag is set.
Rmpq_set_d ($rop, $double);
Rmpq_set_f ($rop, $f); # $f is a Math::GnumMPf object
Rmpq_set_d ($rop, $op);
Rmpq_set_NV($rop, $nv);
Set $rop to the value of the 2nd arg, without rounding.
Assigning an Inf or NaN is a fatal error.
With Rmpq_set_NV, $nv must have its NOK flag set, or the function
will croak. Best to first check NOK_flag($nv), which will return a
non-zero value if and only if the NOK flag is set.
Rmpq_set_str($rop, $str, $base);
Set $rop from $str in the given base $base. The string can be
an integer like "41" or a fraction like "41/152". The fraction
must be in canonical form, or if not then `Rmpq_canonicalize'
must be called. The numerator and optional denominator are
parsed the same as in `Rmpz_set_str'. $base can vary from 2 to
62, or if $base is 0 then the leading characters are used: `0x'
for hex, `0' for octal, or decimal otherwise. Note that this
is done separately for the numerator and denominator, so for
instance `0xEF/100' is 239/100, whereas `0xEF/0x100' is 239/256.
Rmpq_swap($rop1, $rop2);
Swap the values.
####################
COMBINED INITIALIZATION AND ASSIGNMENT
NOTE: Do NOT use these functions if $rop has already
been initialised. Instead use the Rmpq_set* functions
in 'Assignment Functions' (above)
First read the section 'MEMORY MANAGEMENT' (above).
$rop = Math::GMPq->new($arg);
$rop = Math::GMPq::new($arg);
$rop = new Math::GMPq($arg);
Returns a Math::GMPq object with the value of $arg.
$arg can be either an integer (signed integer, unsigned
integer) or a string that represents a numeric value. If $arg is a
string, an optional additional argument that specifies the base of
the number can be supplied to new(). If base is 0 (or not supplied)
then the leading characters of the string are used: 0x or 0X for
hex, 0b or 0B for binary, 0 for octal, or decimal otherwise. Note
that this is done separately for the numerator and denominator, so
for instance 0xEF/100 is 239/100, whereas 0xEF/0x100 is 239/256.
Legal values for the base are 0 and 2..62.
####################
RATIONAL CONVERSIONS
$NV = Rmpq_get_d($op);
Convert $op to a its double-precision value.
$NV = Rmpq_get_NV($op);
Convert $op to an NV using the full precision available to the NV.
If nvtype is 'double', then this is the same as Rmpq_get_d($op).
$str = Rmpq_get_str($op, $base);
Convert $op to a string of digits in base $base. The base may
vary from 2 to 36. The string will be of the form `num/den',
or if the denominator is 1 then just `num'.
###################
RATIONAL ARITHMETIC
Rmpq_add ($rop, $op1, $op2);
Rmpq_add_z($rop, $op1, $z); # $z is a Math::GMPz object
1st arg = 2nd arg + 3rd arg.
(The gmp library doesn't provide an mpq_add_z function.)
Rmpq_sub ($rop, $op1, $op2);
Rmpq_sub_z($rop, $op1, $z); # $z is a Math::GMPz object
Rmpq_z_sub($rop, $z, $op1); # $z is a Math::GMPz object
1st arg = 2nd arg - 3rd arg.
(The gmp library doesn't provide an mpq_sub_z function or
an mpq_z_sub function.)
Rmpq_mul ($rop, $op1, $op2);
Rmpq_mul_z($rop, $op1, $z); # $z is a Math::GMPz object
1st arg = 2nd arg * 3rd arg.
(The gmp library doesn't provide an mpq_mul_z function.)
Rmpq_mul_2exp($rop, $op, $ui);
$rop = $op * (2 ** $ui).
Rmpq_div ($rop, $op1, $op2);
Rmpq_div_z($rop, $op1, $z); # $z is a Math::GMPz object
Rmpq_z_div($rop, $z, $op1); # $z is a Math::GMPz object
1st arg = 2nd arg / 3rd arg.
(The gmp library doesn't provide an mpq_div_z function or
an mpq_z_div function.)
Rmpq_div_2exp($rop, $op, $ui);
$rop = $op / (2 ** $ui).
Rmpq_neg($rop, $op);
$rop = -$op.
Rmpq_abs($rop, $op);
$rop = abs($op).
Rmpq_inv($rop, $op);
$rop = 1 / $op.
##########################
APPLYING INTEGER FUNCTIONS
Rmpq_numref($z, $op); # $z is a Math::GMPz object
Rmpq_denref($z, $op); # $z is a Math::GMPz object
Set $rop to the numerator and denominator of $op, respectively.
Rmpq_get_num($z, $op); # $z is a Math::GMPz oblect
Rmpq_get_den($z, $op); # $z is a Math::GMPz oblect
Rmpq_set_num($rop, $z); # $z is a Math::GMPz oblect
Rmpq_set_den($rop, $z); # $z is a Math::GMPz oblect
Get or set the numerator or denominator of a rational
Direct use of `Rmpq_numref' or `Rmpq_denref' is
recommended instead of these functions.
###################
COMPARING RATIONALS
$si = Rmpq_cmp ($op1, $op2);
$si = Rmpq_cmp_z($op1, $z); # $z is a Math::GMPz object
Compare $op1 and $op2. Return a positive value if 1st arg
is greater than 2nd arg, zero if 1st arg == 2nd arg, and a
negative value if 1st arg < 2nd arg.
To determine if two rationals are equal, `Rmpq_equal' is
faster than `Rmpq_cmp'.
(The gmp library provides mpq_cmp_z only for gmp-6.1.0 and
later but Rmpq_cmp_z is available for all builds of Math::GMPz,
irrespective of the underlying version of gmp.)
$si = Rmpq_cmp_ui($op, $ui1 , $ui2);
$si = Rmpq_cmp_si($op, $si2 , $ui );
$si = Rmpq_cmp_IV($op, $iv1 , $iv2); # $iv1, $iv2, are IVs.
Compare $op1 and 2nd arg/3rd arg. Return a positive value if
$op1 > 2nd arg/3rd arg, zero if $op1 = 2nd arg/3rd arg,
and a negative value if $op1 < 2nd arg/3rd arg.
2nd and 3rd args are allowed to have common factors.
Note that the 3rd (NOT 2nd) arg is unsigned. If you want
to compare $op with 2/-3, make sure that 2nd arg is
'-2' and 3rd arg is '3'.
NOTE:
Rmpq_cmp_IV() requires that the 2nd and 3rd arguments both
have their IOK flag set - otherwise it croaks.
Suggestion: first check the status of the flag of both of
those arguments using IOK_flag($iv),which returns a non-zero
value if and only if the flag in question is set.
$si = Rmpq_cmp_NV($op, $nv);
Return 0 if $op == $nv.
Return 1 if $op > $nv.
Return -1 if $op < $nv
It's a fatal error if $nv is a NaN.
NOTE:
Rmpq_cmp_NV() requires that the 2nd argument
has its NOK flag set - otherwise it croaks.
Suggestion: first check the status of the flag of the
second argument using NOK_flag($nv),which returns a
non-zero value if and only if the flag in question is set.
$si = Rmpq_sgn($op);
Return 1 if $op>0, 0 if $op=0, and -1 if $op < 0.
$bool = Rmpq_equal($op1, $op2); # faster than Rmpq_cmp()
Return non-zero if $op1 and $op2 are equal, zero if they
are non-equal. Although `Rmpq_cmp' can be used for the
same purpose, this function is much faster.
$si = Rmpq_cmp_z($op, $z);# $z is Math::GMPz or Math::GMP object
Return a positive value if $op > $z.
Return zero if $op == $z.
Return a negative value if $op < $z.
################
I/O of RATIONALS
$bytes_written = Rmpq_out_str([$prefix,] $op, $base [, $suffix]);
BEST TO USE TRmpq_out_str INSTEAD.
Output $op to STDOUT, as a string of digits in base $base.
The base may vary from 2 to 36. Output is in the form `num/den'
or if the denominator is 1 then just `num'. Return the number
of bytes written, or if an error occurred, return 0.
The optional first and last arguments ($prefix and $suffix) are
strings that will be prepended/appended to the mpq_out_str
output. $bytes_written does not include the bytes contained in
$prefix and $suffix.
$bytes_written = TRmpq_out_str([$prefix,] $stream, $base, $op, [, $suffix]);
As for Rmpq_out_str, except that there's the capability to print
to somewhere other than STDOUT. Note that the order of the args
is different (to match the order of the mpq_out_str args).
To print to STDERR:
TRmpq_out_str(*stderr, $base, $digits, $op);
To print to an open filehandle (let's call it $fh):
TRmpq_out_str(\*$fh, $base, $digits, $op);
$bytes_read = Rmpq_inp_str($rop, $base);
BEST TO USE TRmpq_inp_str INSTEAD.
Read a string of digits from STDIN and convert them to a rational
in $rop. Any initial white-space characters are read and
discarded. Return the number of characters read (including white
space), or 0 if a rational could not be read.
The input can be a fraction like `17/63' or just an integer like
`123'. Reading stops at the first character not in this form, and
white space is not permitted within the string. If the input
might not be in canonical form, then `mpq_canonicalize' must be
called. $base can be between 2 and 36, or can be 0 in which case the
leading characters of the string determine the base, `0x' or `0X'
for hexadecimal, `0' for octal, or decimal otherwise. The leading
characters are examined separately for the numerator and
denominator of a fraction, so for instance `0x10/11' is 16/11,
whereas `0x10/0x11' is 16/17.
$bytes_read = TRmpq_inp_str($rop, $stream, $base);
As for Rmpq_inp_str, except that there's the capability to read
from somewhere other than STDIN.
To read from STDIN:
TRmpq_inp_str($rop, *stdin, $base);
To read from an open filehandle (let's call it $fh):
TRmpq_inp_str($rop, \*$fh, $base);
#######################
RANDOM NUMBER FUNCTIONS
$state = qgmp_randinit_default();
This is the Math::GMPq interface to the gmp library function
'gmp_randinit_default'.
$state is blessed into package Math::GMPq::Random and will be
automatically cleaned up when it goes out of scope.
Initialize $state with a default algorithm. This will be a
compromise between speed and randomness, and is recommended for
applications with no special requirements. Currently this is
the gmp_randinit_mt function (Mersenne Twister algorithm).
$state = qgmp_randinit_mt();
This is the Math::GMPq interface to the gmp library function
'gmp_randinit_mt'.
Currently identical to fgmp_randinit_default().
$state = qgmp_randinit_lc_2exp($mpz, $ui, $m2exp);
This is the Math::GMPq interface to the gmp library function
'gmp_randinit_lc_2exp'. $mpz is a Math::GMP or Math::GMPz object,
so one of those modules is required in order to make use of this
function.
$state is blessed into package Math::GMPq::Random and will be
automatically cleaned up when it goes out of scope.
Initialize $state with a linear congruential algorithm
X = ($mpz*X + $ui) mod (2 ** $m2exp). The low bits of X in this
algorithm are not very random. The least significant bit will have a
period no more than 2, and the second bit no more than 4, etc. For
this reason only the high half of each X is actually used.
When a random number of more than m2exp/2 bits is to be generated,
multiple iterations of the recurrence are used and the results
concatenated.
$state = qgmp_randinit_lc_2exp_size($ui);
This is the Math::GMPq interface to the gmp library function
'gmp_randinit_lc_2exp_size'.
$state is blessed into package Math::GMPf::Random and will be
automatically cleaned up when it goes out of scope.
Initialize state for a linear congruential algorithm as per
gmp_randinit_lc_2exp. a, c and m2exp are selected from a table,
chosen so that $ui bits (or more) of each X will be used,
ie. m2exp/2 >= $ui.
If $ui is bigger than the table data provides then the function fails
and dies with an appropriate error message. The maximum value for $ui
currently supported is 128.
$state2 = qgmp_randinit_set($state1);
This is the Math::GMPq interface to the gmp library function
'gmp_randinit_set'.
$state2 is blessed into package Math::GMPf::Random and will be
automatically cleaned up when it goes out of scope.
Initialize $state2 with a copy of the algorithm and state from
$state1.
$state = qgmp_randinit_default_nobless();
$state = qgmp_randinit_mt_nobless();
$state = qgmp_randinit_lc_2exp_nobless($mpz, $ui, $m2exp);
$state2 = qgmp_randinit_set_nobless($state1);
As for the above comparable function, but $state is not blessed into
any package. (Generally not useful - but they're available if you
want them.)
qgmp_randseed($state, $mpz); # $mpz is a Math::GMPz or Math::GMP object
qgmp_randseed_ui($state, $ui);
These are the Math::GMPz interfaces to the gmp library functions
'gmp_randseed' and 'gmp_randseed_ui'.
Seed an initialised (but not yet seeded) $state with $mpz/$ui.
Either Math::GMP or Math::GMPz is required for 'gmp_randseed'.
$ui = qgmp_urandomb_ui($state, $bits);
This is the Math::GMPq interface to the gmp library function
'gmp_urandomb_ui'.
Return a uniformly distributed random number of $bits bits, ie. in
the range 0 to 2 ** ($bits - 1) inclusive. $bits must be less than or
equal to the number of bits in an unsigned long.
$ui2 = qgmp_urandomm_ui($state, $ui1);
This is the Math::GMPq interface to the gmp library function
'gmp_urandomm_ui'.
Return a uniformly distributed random number in the range 0 to
$ui1 - 1, inclusive.
qgmp_randclear($state);
Destroys $state, as also does Math::GMPq::Random::DESTROY - two
identical functions.
Use only if $state is an unblessed object - ie if it was initialised
using one of the qgmp_randinit*_nobless functions.
####################
OPERATOR OVERLOADING
Overloading occurs with numbers, strings,Math::GMPq objects and, to a
limited extent, with Math::GMPz objects, and Math::MPFR objects
(iff version 3.13 or later of Math::MPFR has been installed).
Strings are first converted to Math::GMPq objects, then canonicalized.
See the Rmpq_set_str documentation (above) in the section "ASSIGNMENT
FUNCTIONS" regarding permissible string formats.
The following operators are overloaded:
+ - * / **
+= -= *= /= **=
++ --
== != !
< <= > >= <=>
"" abs 0+
=
NOTE: Making use of the '=' overloading is not recommended unless
you understand its caveats. See 'perldoc overload' and
read it thoroughly, including the documentation regarding
'copy constructors'.
Atempting to use the overloaded operators with objects that
have been blessed into some package other than 'Math::GMPq'
or 'Math::MPFR'/'Math::GMPz'/'Math::GMP'/'Math::MPFR' (limited
applications) will not work.
Math::MPFR objects can be provided as the second arg with '+',
'-', '*', '/' and '**' operators, but will work only if Math::MPFR
is at version 3.13 or later - in which case the operation will
return a Math::MPFR object (calculated using default Math::MPFR
precision and default Math::MPFR rounding mode).
For comparisons (==, !=, <, <=, >, >=, <=>) between Math::MPFR and
Math::GMPq objects, you need to invoke the Math::MPFR overloading
as the Math::GMPq overloading does not accommodate such comparisons.
eg - do ($mpfr_obj > $mpq_obj), not ($mpq_obj < $mpfr_obj).
Math::GMPz and Math::GMP objects can be provided as the second
arg with comparison operators ( == != < <= > >= <=> ) and the '+',
'+=', '-', '-=', '*', '*=', '/', '/=', '**' and '**=' operators.
Math::MPFR objects can provided as the second arg with '+', '-',
'*', '/' and '**' operators - in which case the operation will
return a Math::MPFR object.
If $Math::GMPq::RETYPE is set to 1 (as is the default setting), then
Math::MPFR objects can also be provided as the second arg with
'+=', '*=', '-=', '/=' and '**=' operators. In such instances,
the Math::GMPq object becomes (is "retyped" to) a Math::MPFR object
that contains the result of the operation, using default Math::MPFR
precision and default Math::MPFR rounding mode.
Set $Math::GMPq::RETYPE to 0, to disable this capability.
To determine the type and value of the second argument the subroutine
works through the following steps (in order), using the first value
it finds, or croaking if it gets to step 6:
1. If the variable is a UV then that value is used. The variable
is considered to be a UV if the IOK and IsUV flags are set.
2. If the variable is an IV, then that value is used.
The variable is considered to be an IV if the IOK flag is set.
3. If the variable is a string (ie the POK flag is set) then the
value of that string is used. Octal strings must begin with
'0', hex strings must begin with either '0x' or '0X' -
otherwise the string is assumed to be decimal. If the POK
flag is set, but the string is not a valid base 8, 10, or 16
number, the subroutine croaks with an appropriate error
message. If the string is of the form 'numerator/denominator',
then the bases of the numerator and the denominator are
assessed individually. ie '0xa123/ff' is not a valid number
(because 'ff' is not a valid base 10 number). That needs to
be rewritten as '0xa123/0xff'.
4. If the variable is an NV, then that value is used. The
variable is considered to be a NV if the NOK flag is set.
5. If the variable is a Math::GMPq object (or, for operators
specified above, a Math::MPFR/Math::GMP/Math::GMPz object)
then the value of that object is used.
6. If none of the above is true, then the second variable is
deemed to be of an invalid type. The subroutine croaks with
an appropriate error message.
##############
MISCELLANEOUS
$bool = Rmpq_integer_p($op);
Returns true if $op is an integer (ie denominator of $op is 1).
Else returns false. The mpq_integer_p function is not
implemented in gmp.
$si = IOK_flag($sv); # $sv is a perl scalar variable.
$si = NOK_flag($sv);
$si = POK_flag($sv);
Return 0 if $sv's IOK/NOK/POK flag is unset.
Else return 1.
If the IsUV flag is set, then IOK_flag() returns 2, thereby indicating
that both the IOK and IsUV flags are set (and that the integer value
held by $sv should therefore be treated as unsigned).
#####
OTHER
$GMP_version = Math::GMPq::gmp_v;
Returns the version of the GMP library (eg 4.1.3) being used by
Math::GMPq. The function is not exportable.
$GMP_cc = Math::GMPq::__GMP_CC;
$GMP_cflags = Math::GMPq::__GMP_CFLAGS;
If Math::GMPq has been built against gmp-4.2.3 or later,
returns respectively the CC and CFLAGS settings that were used
to compile the gmp library against which Math::GMPq was built.
(Values are as specified in the gmp.h that was used to build
Math::GMPq.)
Returns undef if Math::GMPq has been built against an earlier
version of the gmp library.
(These functions are in @EXPORT_OK and are therefore exportable
by request. They are not listed under the ":mpq" tag.)
$major = Math::GMPq::__GNU_MP_VERSION;
$minor = Math::GMPq::__GNU_MP_VERSION_MINOR;
$patchlevel = Math::GMPq::__GNU_MP_VERSION_PATCHLEVEL;
Returns respectively the major, minor, and patchlevel numbers
for the GMP library version used to build Math::GMPq. Values are
as specified in the gmp.h that was used to build Math::GMPq.
(These functions are in @EXPORT_OK and are therefore exportable
by request. They are not listed under the ":mpq" tag.)
################
FORMATTED OUTPUT
NOTE: The format specification can be found at:
http://gmplib.org/manual/Formatted-Output-Strings.html#Formatted-Output-Strings
However, the use of '*' to take an extra variable for width and
precision is not allowed in this implementation. Instead, it is
necessary to interpolate the variable into the format string - ie,
instead of:
Rmpq_printf("%*Zd\n", $width, $mpz);
we need:
Rmpq_printf("%${width}Zd\n", $mpz);
$si = Rmpq_printf($format_string, $var);
This function changed with the release of Math-GMPq-0.27.
Now (unlike the GMP counterpart), it is limited to taking 2
arguments - the format string, and the variable to be formatted.
That is, you can format only one variable at a time.
If there is no variable to be formatted, then the final arg
can be omitted - a suitable dummy arg will be passed to the XS
code for you. ie the following will work:
Rmpq_printf("hello world\n");
Returns the number of characters written, or -1 if an error
occurred.
$si = Rmpq_fprintf($fh, $format_string, $var);
This function (unlike the GMP counterpart) is limited to taking
3 arguments - the filehandle, the format string, the variable
to be formatted. That is, you can format only one variable at a time.
If there is no variable to be formatted, then the final arg
can be omitted - a suitable dummy arg will be passed to the XS
code for you. ie the following will work:
Rmpq_fprintf($fh, "hello world\n");
Other than that, the rules outlined above wrt Rmpq_printf apply.
Returns the number of characters written, or -1 if an error
occurred.
$si = Rmpq_sprintf($buffer, $format_string, $var, $buflen);
This function (unlike the GMP counterpart) is limited to taking
4 arguments - the buffer, the format string, the variable to be
formatted and the size of the buffer. If there is no variable to
be formatted, then the third arg can be omitted - a suitable
dummy arg will be passed to the XS code for you. ie the following
will work:
Rmpf_sprintf($buffer, "hello world", 12);
$buffer must be large enough to accommodate the formatted string.
The formatted string is placed in $buffer.
Returns the number of characters written, or -1 if an error
occurred.
$si = Rmpq_snprintf($buffer, $bytes, $format_string, $var, $buflen);
Form a null-terminated string in $buffer. No more than $bytes
bytes will be written. To get the full output, $bytes must be
enough for the string and null-terminator. $buffer must be large
enough to accommodate the string and null-terminator, and is
truncated to the length of that string (and null-terminator).
The return value is the total number of characters which ought
to have been produced, excluding the terminating null.
If $si >= $bytes then the actual output has been truncated to
the first $bytes-1 characters, and a null appended.
This function (unlike the GMP counterpart) is limited to taking
5 arguments - the buffer, the maximum number of bytes to be
returned, the format string, the variable to be formatted and
the size of the buffer.
If there is no variable to be formatted, then the 4th arg can
be omitted - a suitable dummy arg will be passed to the XS code
for you. ie the following will work:
Rmpf_snprintf($buffer, 6, "hello world", 12);
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