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Double check x87 precision correctness
x86 manual had a couple statements that caught my eye.
> The Precision control (PC) field comprises bits [9:8] of the x87 control word (“x87 Control Word Register (FCW)” on page 292). This field specifies the precision of floating-point calculations for the FADDx, FSUBx, FMULx, FDIVx, and FSQRT instructions, as shown in Table 6-11.
I think we modify precision on more than those instructions listed. Might need to check that.
Also:
> x87 computations are carried out in double-extended-precision format, so that the transcendental functions provide results accurate to within one unit in the last place (ulp) for each of the floating- point data types.
Might want to double check that we have the transcendental accuracy correct.
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