MSC: unsigned _control87( unsigned new, unsigned mask )

	- prototype in float.h

	- used to change floating point handling and exception masking
	- new = contains corresponding bit values for any bit set in "mask"
		to be moved into the coprocessor control word
	- mask	= zero; gets floating-point coprocessor control word
		= non-zero; if any bit is set, the corresponding bit in
		  "new" is moved into the coprocessor control word
	- returns floating-point coprocessor control word
	- default control word is the logical OR of: IC_AFFINE, RC_NEAR,
	  PC_64, EM_DENORMAL, EM_UNDERFLOW, EM_INEXACT


	Control Word Mask and Bits

	MCW_EM		interrupt exception control
	MCW_IC		infinity control
	MCW_RC		rounding control
	MCW_PC		precision control

	Exception Masks

	EM_INVALID	invalid
	EM_DENORMAL	denormal
	EM_ZERODIVIDE	zero divide
	EM_OVERFLOW	overflow
	EM_UNDERFLOW	underflow
	EM_INEXACT	inexact (precision)

	Infinity Control

	IC_AFFINE	affine
	IC_PROJECTIVE	projective

	Rounding Control

	RC_CHOP		truncate
	RC_UP		round up
	RC_DOWN		round down
	RC_NEAR		near

	Precision Control

	PC_24		24 bits precision
	PC_53		53 bits precision
	PC_64		64 bits precision

	User Status Word Bits

	SW_INVALID	invalid
	SW_DENORMAL	denormal
	SW_ZERODIVIDE	zero divide
	SW_OVERFLOW	overflow
	SW_UNDERFLOW	underflow
	SW_INEXACT	inexact precision

	Invalid Subconditions (if SW_INVALID)

	SW_UNEMULATED	unemulated instruction
	SW_SQRTNEG	square root of a neg number
	SW_STACKOVERFLOW  FP stack overflow
	SW_STACKUNDERFLOW FP stack underflow

	Floating Point Errors

	FPE_INVALID
	FPE_DENORMAL
	FPE_ZERODIVIDE
	FPE_OVERFLOW
	FPE_UNDERFLOW
	FPE_INEXACT
	FPE_UNEMULATED
	FPE_SQRTNEG
	FPE_STACKOVERFLOW
	FPE_STACKUNDERFLOW
	FPE_EXPLICITGEN

	- see	_clear87()   _status87()