Use math/bits.RotateLeft64 for word rotations - #6
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Replace the manual ((x << r) | (x >> (64-r))) rotate-left idiom in the encrypt paths, and its ((x << (64-r)) | (x >> r)) rotate-right inverse in the decrypt paths, with bits.RotateLeft64(x, r) and bits.RotateLeft64(x, -r) respectively. With constant rotation amounts this compiles to a single ROL/ROR instruction (identical codegen, constant-time), while reading far closer to the spec. Purely mechanical: every changed line is a rotation, and the unchanged known-answer test vectors confirm the behavior is identical.
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Replace the manual ((x << r) | (x >> (64-r))) rotate-left idiom in the encrypt paths, and its ((x << (64-r)) | (x >> r)) rotate-right inverse in the decrypt paths, with bits.RotateLeft64(x, r) and bits.RotateLeft64(x, -r) respectively. With constant rotation amounts this compiles to a single ROL/ROR instruction (identical codegen, constant-time), while reading far closer to the spec.
Purely mechanical: every changed line is a rotation, and the unchanged known-answer test vectors confirm the behavior is identical.