I'm a little confused about the latter suggestion, since I'm not sure integer operations would "sort out" floating point stuff,

That's my understanding also; but I was hoping ... :)

I have native 64-bit ints; so combining two of those to give me fixed point would give huge precision; no need to move to two 128-bit integers.

But I'm fuzzy on the implementation of fixed point floats using two ints. If you come across any pointers/notes/implementations I'd love to hear of it.

My current approach is to think about it in two steps: First, if 128-bit ints are not supported natively, one needs routines to handle normal arithmetic operations on those (so you don't need to worry whether they are 2x 64-bit ints or even 4x 32-bit ints). That shouldn't be too difficult (it'd be the same basic idea as doing 16-bit math on an 8-bit uC), plus there seem to be a couple of libraries out there. E.g. Boost apparently has a int128_t and bigger (http://www.boost.org/doc/libs/1_53_0/libs/multiprecision/doc/html/boost_multiprecision/tut/ints/cpp_int.html)... Math::Int128 apparently tries to use the native 128-bit ints, which as far as I understand from what I've read so far are not "officially" supported by MS, which would be my guess as to why the module has some CPAN Testers failures on Windows.

Second, use those routines to implement the fixed-point stuff. Addition and subtraction is pretty trivial; multiplication would either require a temporary 256-bit integer or some rounding; still doing research on the latter... you've piqued my curiosity :-)

you've piqued my curiosity :-)

Update: I forgot the package statements. D'oh! (Code updated)

This is what I have so far. Not working yet because of an IC problem that I've encountered before, but can't remember how to fix; and the math is almost certainly wrong as is; but I threw it together to try and get a starting point:

#! perl -slw
use Config; package F128;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<END_C,  NAME => 'F128', CLEAN_AFTER_BUILD =>0, TYPEM
+APS => './F128.typemap';
#include "../C/mytypes.h"
#define CLASS "F128"

typedef struct { U64 scale; U64 precision; } F128;

F128 *new( I64 scale, U64 precision ) {
    F128 *n = malloc( sizeof( F128 ) );
    n->scale = scale;
    n->precision = precision;
    return n;
}

F128 *add( F128 *a, F128 *b ) {
    if( a->scale != b->scale ) {
        while( a->scale > b->scale ) {
            a->scale >>= 1;
            a->precision <<= 1;
        }
        while( a->scale < b->scale ) {
            a->scale <<= 1;
            a->precision >>= 1;
        }
    }
    a->precision += b->precision;
    return a;
}

F128 *multiply( F128 *a, F128 *b ) {
    a->precision *= b->precision;
    a->scale += b->scale;
    return a;
}

SV *toString( F128 *a ) {
    char *out = malloc( a->scale );
    U32 c = sprintf( out, "%I64ue%I64i", a->precision, a->scale );
    return newSVpv( out, c );
}

void DESTROY( F128 *a ) {
    free( a );
    return;
}

END_C
package main;
my $Fa = F128::new( -10, 45 );
my $Fb = F128::new( -10, 45 );
my $Fc = F128::new( -10, 45 );

print $Fa->toString;

$Fa->add( $Fb );
print $Fa->toString;

$Fc->multiply( $Fb );
print $Fc->toString;
[download]

The typemap:

TYPEMAP
const char  * T_PV
F128        * O_OBJECT
U64           T_UV
I64           T_IV
U8            T_UV
U8          * T_PV

INPUT
O_OBJECT
    if( sv_isobject($arg) && ( SvTYPE( SvRV($arg) ) == SVt_PVMG ) )
            $var = INT2PTR( $type, SvIV( (SV*)SvRV( $arg ) ) );
    else{
            warn( \"${Package}::$func_name() -- $var is not a blessed 
+SV reference\" );
            XSRETURN_UNDEF;
    }

OUTPUT

# The Perl object is blessed into 'CLASS', which should be a
# char* having the name of the package for the blessing.
O_OBJECT
        sv_setref_pv( $arg, (char *)CLASS, (void*)$var );
[download]

I'm currently getting:

45e-10
90e-10
2025e-20
[download]

Which is almost there for my requirements.

And I know its a trivial fix, but .... I can't remember what. syphilis Got your ears on?.

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