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+; By: Jeffrey Nonken
+
+ page 60,132
+ .286
+
+_text segment byte public 'code'
+_text ends
+_data segment word public 'data'
+_data ends
+const segment word public 'const'
+const ends
+_bss segment word public 'bss'
+_bss ends
+dgroup group const, _bss, _data
+ assume cs: _text, ds: nothing
+
+_data segment word public 'data'
+ even
+env_8087 dw 47 dup (?)
+norm_8087 dw 177fh
+_data ends
+
+_text segment byte public 'code'
+;
+; This code saves the 80x87 enviroment and sets up our own. First, this
+; assumes you are running an 80287; the 8087 may require more FWAIT
+; operations. Second, I decided that I didn't want to handle exceptions, so
+; I simply disabled them. That means that if the 80x87 gets an invalid result
+; (such as divide-by-zero) the 80x87 will continue to run and will produce
+; invalid results until the end of your current calculation. Anything that
+; depends on the results will, of course, also be invalid. If you want
+; exceptions to be handled, get documentation for the 80x87 and you will
+; see how to set norm_8087 (above) to suit your needs. If you are running
+; an 8087 and don't know where to put FWAIT instructions, you can always
+; add one after each floating-point instruction. NOTE: FWAIT is synonymous
+; to WAIT. They are the same instruction.
+;
+; This was written for TURBO C and will also work with MSC. It should work
+; with any programming language with no more than minor changes in the
+; label names or the interface. Consult your compiler manual for more detail.
+; I wrote this so it would work with either the tiny or small models.
+; Actually, it will probably work with any of the models. You should be
+; able to assemble this with MASM and link it right in.
+;
+; extern save_8087();
+; extern restore_8087();
+;
+ public _save_8087
+_save_8087 proc near
+ cli ; no interruptions!
+ lea bx,dgroup:env_8087 ; point to save area
+ fwait ; make sure processor is ready
+ fnsave [bx] ; save the 8087 environment
+ lea bx,dgroup:norm_8087 ; point to our new 8087 setup
+ mov ax,[bx] ; get it
+ fldcw [bx] ; set it
+ fwait
+ sti ; restore interrupts
+ ret
+_save_8087 endp
+
+ public _restore_8087
+_restore_8087 proc near
+ cli ; no interruptions!
+ lea bx,dgroup:env_8087 ; point to saved 8087 stuff
+ frstor [bx] ; restore the 8087 environment
+ sti ; restore interrupts
+ ret
+_restore_8087 endp
+
+_text ends
+
+ end