change IF of Modp::init

include/mcl/gmp_util.hpp

@@ -877,10 +877,11 @@ struct Modp {
 		mcl::gmp::setArray(&b, x, mcl::gmp::getUnit(x), unitSize);
 		assert(b);
 	}
-	void init(const mpz_class& p, size_t unitSize)
+	void init(const mpz_class& p)
 	{
 		p_ = p;
-		N_ = unitSize;
+		size_t bitSize = mcl::gmp::getBitSize(p);
+		N_ = (bitSize + unitBitSize - 1) / unitBitSize;
 		u_ = (mpz_class(1) << (unitBitSize * 2 * N_)) / p_;
 		a_ = mpz_class(1) << (unitBitSize * (N_ + 1));
 	}

test/fp_test.cpp

@@ -798,7 +798,7 @@ void modpTest()
 		(mpz_class(1) << Fp::getOp().N * mcl::fp::UnitBitSize * 2) - 1,
 	};
 	mcl::Modp modp;
-	modp.init(p, Fp::getUnitSize());
+	modp.init(p);
 	for (size_t i = 0; i < CYBOZU_NUM_OF_ARRAY(tbl); i++) {
 		const mpz_class& x = tbl[i];
 		mpz_class r1, r2;