[libre-riscv-dev] [Bug 44] IEEE754 FPU inverse-sqrt

[bugzilla-daemon at libre-riscv.org]

http://bugs.libre-riscv.org/show_bug.cgi?id=44

--- Comment #15 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #14)
> looking at the diagram from ep08-21.pdf on page 36 (figure 3.15)
> 
> * q[j+1] in radix 2 is a 2-bit signed binary number, -1 0 or +1
>   (top of p35), in binary -1 = 0b10, 0 = 0b00, 1 = 0b01
shouldn't that be -1 = 0b11 assuming it's in 2s complement?
> 
> * |q[j+1]| probably means "absolute value" of q[j+1], in other words
>   when q[j+1] == 0b00, return 0b00, and when q[j+1] == 0b10 (-1),
>   return 0b10 (+1).
I think you meant 0b11 (-1), return 0b01 (+1). 
Even if they're not 2s complement, 1 and -1 shouldn't be identical.

I could be wrong, since I didn't actually check the paper.

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