|P is for Practical|
You missed the point again. The rounding mode being queried or altered by the OP, is that of the math coprocessor and is applied to the results of all FP operations done by it. The 4 modes are as defined by the IEEE Floating Point standard. The two calls, fe(get|set)round are C/C++ compiler provided functions to get/set that hardware rounding mode.
Moving to using software emulated, infinite precision FP to achieve the same end would for most applications be a disaster. With Math::BigFloat, FP calculations run anything from a few hundred to a few 10s of thousands times more slowly depending upon the configuration and underlying libraries used. Okay if your calculating the final cost of a few dozen items in an IO bound shopiing cart application, but for any kind of serious math, way too slow.
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In reply to Re^2: Is there a better way to call fe(get|set)round?