Via: uk.ac.ulcc.vmsfe; Fri, 8 Oct 1993 13:41:59 +0100 Date: Fri, 8 Oct 93 13:41 GMT From: "Kevin Ashley, Systems Development, ULCC" To: DJGPP Subject: Novice question on FP use and emulation I'm a relative newcomer to PC programming although I have many years experience on other (slightly bigger :-)) systems. I know next to nothing about Intel processors, so please bear with me... I recently acquired djgpp 1.09 for my Dell 486-based machine. I've been extremely pleased with it and have already ported a number of useful applications to DOS using it. However, I am confused about a number of issues regarding floating point: (1) The manual says that the compiler shouldn't issue floating point instructions unless you compile floating point code. But I find that, even if I compile the classic "hello world" program, the compiler bombs out with an exception unless I set the 387 enviroment variable to cause an emulator to be used. (2) If I DO compile floating point code, set the 387 variable for an emulator, but don't explicitly specify an emulator in the GO32 variable, I don't get error messages, but I find that every floating-point constant in the generated code is integer -1 (i.e. 4 or 8 bytes of FFFFFFF..) Also, at runtime, every floating-point result is the same. (3) I get the same results if I use the djgpp-supplied emulator. (4) If I use the alternate emulator (wmemu ? I can't remember the name and don't have access to my system right now, but it's the one without sources) floating point seems to work fine. I'm happy in that I have a solution that works (use the emulator without sources) but I'm unhappy in that I don't understand the other behaviour. What's more, I had earlier had a (presumably mistaken) impression that 486 processors performed floating-point instructions themselves, without the need for a 387 co-processor. I seem to be wrong. So what sort of co-processor goes with a 486 ? Thanks for any replies. ------------------------------------------------------------------------------ Kevin Ashley K DOT Ashley AT Ulcc DOT ac DOT uk Systems Development Group Manager ...ukc!ncdlab!K.Ashley University of London Computer Centre.