Math::NV - compare the NV values that perl assigns with C and MPFR
use Math::NV qw(:all); $bool = is_eq('1e-298'); $bool = is_eq_mpfr('1e-298'); # iff Math::MPFR is available If $bool is true, this suggests there is quite possibly no bug in the assignment of the specified value. If $bool is false, this implies that at least one of perl && C (wrt is_eq) or mpfr (wrt is_eq_mpfr) suffer a bug in assigning the specified value. IME, it's perl that's usually wrong - though I've struck buggy assignments with C. I've not yet found a case where mpfr assigns incorrectly - and I firmly expect that I won't ever find such a bug with that library. All mpfr values are assigned with a rounding mode of "to nearest, ties to even". (This could be made configurable if requested.)
$bool = is_eq($str); Returns true if the value perl assigns to an NV from the string $str is equal to the value C assigns to the C type specified by $Config{nvtype} from the same string. Else returns false - which implies that either perl or C is buggy in its assignment of that value. (Or they could both be buggy.) $bool = is_eq_mpfr($str); Returns true if the value perl assigns from the string $str is equal to the value mpfr assigns from the same string. Else returns false - which implies that either perl or mpfr is buggy in its assignment of that value. (Or they could both be buggy - though it's very unlikely that mpfr suffers such a bug.) $nv = nv($str); # scalar context ($nv, $iv) = nv($str); # list context On perls whose NV is a C "double", assigns to $nv the value that the C standard library function strtod($str) assigns. On perls whose NV is a C "long double", assigns to $nv the value that the C standard library function strtold($str) assigns. On perls whose NV is a C "__float128", assigns to $nv the value that the C standard library function strtofloat128($str) assigns. In list context, also returns the number of characters that were unparsed (ignored). Generally you'll want $str to be a string - eg the string "2.3", rather than the NV 2.3. Failure to adhere to this will result in a warning - though you can disable this warning by setting $Math::NV::no_warn to 1. $hex = nv_mpfr($str, [$bits]); If $bits is not specified, it will be set to the value returned by mant_dig() - which is the appropriate value for the current perl that is being run. Valid values for $bits are 53 (double), 64 (long double), 106 (double-double) and 113 (__float128). Other values will cause an error. Uses the mpfr library to assign the value represented by $str as a double or long double or double-double or __float128 (as determined by the value of $bits). It then returns a hex dump of the bytes that make up that C data type. For example, nv_mpfr('1e+127', 53) returns 5a4d8ba7f519c84f. This is the same as should be returned by scalar(reverse(unpack("h*", pack("d<", 1e+127)))) except that, on my Windows machine, it returns 5a4d8ba7f519c851 . (Yes, perl's assignment of that value is out by 2 ULP's.) For the double-double, the returned scalar is a reference to a list that contains 2 elements - the hex dump of the most significant double, and the hex dump of the least siginificant double. For all other types, the returned scalar contains the hex dump of the given value. The enticement to use this function in preference to nv() is twofold: 1) mpfr reliably sets floating point values correctly (whereas C is more likely to suffer bugs); 2) nv_mpfr() can provide hex dumps for any of the four data types (double, long double, double-double and __float128), whereas nv() returns only the value for whichever data type is specified by $Config{nvtype}. Note, however, that for nv_mpfr() to return the hex form of the __float128 type, the mpfr library (as used by Math::MPFR) needs to have been built using the configure option --enable-float128, and this configure option is only available with mpfr-3.2.0 or later. As is the case with nv(), you'll generally want $str to be a string. For example, specify the string "2.3", rather than the NV 2.3. Failure to adhere to this will result in a warning - though you can disable this warning by setting $Math::NV::no_warn to 1. $nv_type = nv_type(); Returns "double", "long double", or "__float128" depending upon the way perl has been configured. The expectation is that it returns the same as $Config{nvtype}. (Please file a bug report if you find otherwise.) $digits = mant_dig(); Returns the number of bits the NV mantissa contains. This is normally 53 if nv_type() is double - otherwise usually (but by no means always) 64. It returns the value of the C macro DBL_MANT_DIG, LDBL_MANT_DIG, or FLT128_MANT_DIG depending upon whichever is appropriate for perl's configuration. ($mantissa, $exponent, $precision) = ld2binary($nv); Uses code taken from tests/tset_ld.c in the mpfr library source and returns a base 2 representation of the value contained in the NV $nv - irrespective of whether the NV type ($Config{nvtype}) is double, long double or __float128. $mantissa is the mantissa (significand). $exponent is the exponent. $precision is the precision (in bits) of the mantissa - trailing zero bits are not counted. ($mantissa, $exponent, $precision) = ld_str2binary($str); Uses code taken from tests/tset_ld.c in the mpfr library source and returns a base 2 representation of the value of the NV represented by the string $str - irrespective of whether the NV type ($Config{nvtype}) is double, long double or __float128. $mantissa is the mantissa (significand). $exponent is the exponent. $precision is the precision (in bits) of the mantissa - trailing zero bits are not counted. $nv = bin2val($mantissa, $exponent, $precision); Takes the return values of ld_str2binary() or ld2binary() and returns the original NV. (Probably doesn't work if the original NV is an inf or a nan.) Cprintf($fmt, $nv); Uses C's printf() function to format the NV $nv, according to the formatting specified by the string $fmt. $string = Csprintf($fmt, $nv, $buffer_size); Uses C's sprintf() function to format the NV $nv, according to the formatting specified by the string $fmt - and returns the result to $string. It's the responsibility of the caller to ensure that $buffer_size specifies a large enough number of characters to accommodate C's sprintf formatting of $nv.
$Math::NV::no_mpfr At startup, NV.pm runs "eval{require Math::MPFR;};". $Math::NV::no_mpfr is automatically set to 0 (if Math::MPFR loads) or to $@ (if Math::MPFR fails to load). Can subsequently be overwritten by assigning directly to it. $Math::NV::no_warn Initially set to 0 - which means that if either nv(), nv_mpfr(), is_eq() or is_eq_mpfr() are handed an argument that is not a string, then a warning will be emitted. To disable this warning, simply assign 1 (or any other true numeric value) to this variable.
This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself. Copyright 2013-15 Sisyphus
Sisyphus <sisyphus at(@) cpan dot (.) org>
To install Math::NV, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Math::NV
CPAN shell
perl -MCPAN -e shell install Math::NV
For more information on module installation, please visit the detailed CPAN module installation guide.