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@ -202,20 +202,36 @@ static rct::keyV vector_powers(const rct::key &x, size_t n)
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}
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}
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/* Given a scalar, return the sum of its powers from 0 to n-1 */
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/* Given a scalar, return the sum of its powers from 0 to n-1 */
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static rct::key vector_power_sum(const rct::key &x, size_t n)
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static rct::key vector_power_sum(rct::key x, size_t n)
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{
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{
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if (n == 0)
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if (n == 0)
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return rct::zero();
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return rct::zero();
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rct::key res = rct::identity();
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rct::key res = rct::identity();
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if (n == 1)
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if (n == 1)
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return res;
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return res;
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rct::key prev = x;
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for (size_t i = 1; i < n; ++i)
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const bool is_power_of_2 = (n & (n - 1)) == 0;
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if (is_power_of_2)
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{
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{
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if (i > 1)
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sc_add(res.bytes, res.bytes, x.bytes);
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sc_mul(prev.bytes, prev.bytes, x.bytes);
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while (n > 2)
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sc_add(res.bytes, res.bytes, prev.bytes);
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{
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sc_mul(x.bytes, x.bytes, x.bytes);
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sc_muladd(res.bytes, x.bytes, res.bytes, res.bytes);
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n /= 2;
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}
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}
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else
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{
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rct::key prev = x;
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for (size_t i = 1; i < n; ++i)
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{
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if (i > 1)
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sc_mul(prev.bytes, prev.bytes, x.bytes);
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sc_add(res.bytes, res.bytes, prev.bytes);
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}
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}
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}
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return res;
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return res;
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}
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}
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