New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Double check x87 precision correctness #4191

Open

Sonicadvance1 opened this issue Dec 4, 2024 · 0 comments

Member

Sonicadvance1 commented Dec 4, 2024 •

edited

Loading

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.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment