浮動小数点数演算を使わずに高速に平方数を判定します。 (実装例はRustですがC++でも書けると思います) use std::num::Wrapping; pub fn is_square(x: u64) -> bool { let xtz = x.trailing_zeros(); if x == 0 { return true; } else if xtz & 1 != 0 { return false; } let x = Wrapping(x >> xtz); let mut y = Wrapping(1_u64); for _ in 0..5 { y = ((Wrapping(3_u64) - y * y * x) * y) >> 1; } let mut xrt = x * y; if xrt.0 & (1 << 32) != 0 { xrt = -xrt; } let xrt
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