DOCERR: Some Coprocessor Instructions Not Emulated (45146)

SUMMARY

The /E option of the Microsoft Macro Assembler (MASM) 5.0 and 5.1 directs the assembler to generate data and code as it is expected by coprocessor emulator libraries. The /FPi option and the OPTION EMULATOR directive provide the same functionality, starting with MASM version 6.0.

The emulator libraries are available with the high-level languages like C, BASIC, FORTRAN, and Pascal. However, the emulator libraries do not support all coprocessor instructions. The following error message will result when an unsupported coprocessor instruction is executed:

run-time error M6107: MATH - floating-point error: unemulated

MORE INFORMATION

The following is the list of unemulated coprocessor instructions in MASM 5.1:

   FBLD                    FSAVE
   FBSTP                   FSETPM
   FCOS                    FSIN
   FDECSTP                 FSINCOS
   FINCSTP                 FSTENV
   FINIT                   FUCOM
   FLDENV                  FUCOMP
   FNOP                    FUCOMPP
   FPREM1                  FXTRACT
   FRSTOR

The following is the list of unemulated coprocessor instructions in MASM 6.0 as indicated on page 161 of the "Microsoft Macro Assembler Programmer's Guide":

   FCOS                    FSAVE32
   FDECSTP                 FSETPM
   FINCSTP                 FSIN
   FPREM1                  FSINCOS
   FRSTOR                  FUCOM
   FRSTOR16                FUCOMP
   FRSTOR32                FUCOMPP
   FSAVE                   FXTRACT
   FSAVE16

However, this list is not complete. When tested with the run-time libraries from Microsoft C/C++ 7.0, the following instructions also result in the M6107 error

   FBLD                    FLDENV
   FBSTP                   FNOP
   FINIT                   FSTENV

In addition, a few of the names are incorrect

   FRSTOR16   should be    FRSTORW
   FRSTOR32   should be    FRSTORD
   FSAVE16    should be    FSAVEW
   FSAVE32    should be    FSAVED

The following stand-alone assembler sample reproduces the M6107 error for the instruction FBLD. Note that the C run-time code must be brought in. In this case, the small model emulator library (slibce) is used.

Sample Code

; Assemble options needed: /Cx /link slibce

OPTION EMULATOR
.MODEL small, C
PUBLIC main

.DATA
packbcd TBYTE 0

.CODE
main:
   fbld packbcd
END