Tell me about the DM42

[Thomas Okken]

(12-20-2017 02:23 PM)grsbanks Wrote:  As far as program bytes are concerned, Free42 uses up the same amount of space as the HP-42S with the exception of very slightly different storage of numerical literals in some cases.

No, Free42 reports the same program sizes as the HP-42S, but it uses roughly double the space for program storage.

The shortest instructions on the 42S take up one byte, two in Free42; most 42S instructions with arguments take up two bytes, four in Free42; embedded GTO and XEQ offsets are 8 or 12 bits on the 42S, 32 bits in Free42; numbers are stored as a sequence of digits on the 42S, and in native integer or floating-point format in Free42, which can be shorter but is usually longer.

Most Free42 users are probably unaware of all this, since programs are imported and exported in the same "raw" format that Emu42 uses, which is the format in which the real HP-42S stores programs... but Free42 does this by converting between that format and its totally different internal format whenever it imports or exports programs.

Early versions of Free42 actually offered the choice between reporting true program size and HP-42S-compatible program size. I ended up dropping the "true size" option because, on platforms with megabytes of RAM, the actual size of programs didn't matter, while the 42S-compatible byte count still provided a useful, if weak, integrity check (except for the 1000 turning into 1E3 thing Free42 does, which grsbanks alluded to). Given that memory is much more limited in the DM42 than on a PC or smartphone, and it seems entirely possible that some people might fill it up, perhaps I should restore the "actual program size" option.