I think this will do it:
ASSERT("840003123456770"=Get_value ("02ABC877FAFB0200"))
using primary school maths only...
--
C_TEXT($1;$0)
Case of
: (Count parameters=1)
C_TEXT(hex;$e;$total)
C_LONGINT($i)
$hex:=$1
For ($i;1;Length($hex);2)
//hex byte code to integer string
$byte:=Substring($hex;$i;2)
$code:="<!--#4deval 0x"+$byte+"-->"
PROCESS 4D TAGS($code;$code)
If ($i=1)
$value:=$code
$e:="1"
Else
//exp beyond 256^5 is a bit hazy, might as well do it using text
EXECUTE METHOD(Current method name;$e;$e;"256";"*")
//base-10 text multiplication
EXECUTE METHOD(Current method name;$value;$code;$e;"*")
End if
//base-10 text addition
EXECUTE METHOD(Current method name;$total;$total;$value;"+")
End for
$0:=$total
: (Count parameters=3)
C_TEXT($a;$b;$r)
$a:=String($1)
$b:=String($2)
$operand:=$3
If ($a="")
$a:="0"
End if
If ($b="")
$b:="0"
End if
//no checking for non-numbers, negative numbers, e
C_LONGINT($lena;$lenb)
$lena:=Length($a)
$lenb:=Length($b)
C_LONGINT($c;$d;$e;$f;$m1;$m2;$m3)
ARRAY LONGINT($mm;0)
Case of
: ($operand="*")
$d:=0
For ($x;$lena;1;-1)
$c:=1
For ($y;$lenb;1;-1)
$m:=Num($a[[$x]])*Num($b[[$y]])
$e:=$m%10
$f:=$m\10
If (($c+$d+2)>Size of array($mm))
ARRAY LONGINT($mm;$c+$d+2)
End if
$m1:=$mm{$c+$d}+$e
$m2:=$mm{$c+$d+1}+$f+($m1\10)
$m3:=$mm{$c+$d+2}+($m2\10)
$mm{$c+$d}:=$m1%10
$mm{$c+$d+1}:=$m2%10
$mm{$c+$d+2}:=$m3
$c:=$c+1
End for
$d:=$d+1
End for
: ($operand="+")
$len:=Choose($lena>$lenb;$lena;$lenb)
$a:=Substring(("0"*$len)+$a;$lena+1)
$b:=Substring(("0"*$len)+$b;$lenb+1)
$c:=1
For ($x;$len;1;-1)
$m:=Num($a[[$x]])+Num($b[[$x]])
$e:=$m%10
$f:=$m\10
If (($c+2)>Size of array($mm))
ARRAY LONGINT($mm;$c+2)
End if
$m1:=$mm{$c}+$e
$m2:=$mm{$c+1}+$f+($m1\10)
$m3:=$mm{$c+2}+($m2\10)
$mm{$c}:=$m1%10
$mm{$c+1}:=$m2%10
$mm{$c+2}:=$m3
$c:=$c+1
End for
End case
//filter preceeding zeros and stringify
$r:="0"
C_LONGINT($i;$len)
$len:=Size of array($mm)
For ($i;$len;1;-1)
If ($r="0")
$r:=""
End if
$r:=$r+String($mm{$i})
End for
$0:=$r
End case
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