When calculating the Elligator 2 forward map, use -b if required. #12
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Per section 5.5 of the Elligator paper:
"Here |b| means b if b \in {0,1,...,(q - 1)/2}, otherwise b."
The old code would sometimes return representatives that are 255 bits
in length, which is incorrect (#S = (q + 1)/2).
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I have a C++ version of this code, and a user notified me of this a while ago, but I haven't gotten around to looking into it till now.
Per section 5.5 of the Elligator paper:
"Here |b| means b if b \in {0,1,...,(q - 1)/2}, otherwise b."
The old code would sometimes return representatives that are 255 bits in length, which is incorrect (#S = (q + 1)/2).