From d51fd79c86954a443b1c7ce67d7bcdb8a63ddedb Mon Sep 17 00:00:00 2001
From: MITSUNARI Shigeo <herumi@nifty.com>
Date: Tue, 26 May 2020 11:10:56 +0900
Subject: [PATCH] setBigEndianMod

---
 include/mcl/bn.h               |  2 ++
 include/mcl/fp.hpp             | 37 ++++++++++++++++++++++++++++++++++
 include/mcl/impl/bn_c_impl.hpp |  9 ++++++++-
 include/mcl/mapto_wb19.hpp     |  7 ++-----
 4 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/include/mcl/bn.h b/include/mcl/bn.h
index b2211b7..905733d 100644
--- a/include/mcl/bn.h
+++ b/include/mcl/bn.h
@@ -317,9 +317,11 @@ MCLBN_DLL_API mclSize mclBnFp_getLittleEndian(void *buf, mclSize maxBufSize, con
 // set (buf mod r) to x
 // return 0 if bufSize <= (byte size of Fr * 2) else -1
 MCLBN_DLL_API int mclBnFr_setLittleEndianMod(mclBnFr *x, const void *buf, mclSize bufSize);
+MCLBN_DLL_API int mclBnFr_setBigEndianMod(mclBnFr *x, const void *buf, mclSize bufSize);
 // set (buf mod p) to x
 // return 0 if bufSize <= (byte size of Fp * 2) else -1
 MCLBN_DLL_API int mclBnFp_setLittleEndianMod(mclBnFp *x, const void *buf, mclSize bufSize);
+MCLBN_DLL_API int mclBnFp_setBigEndianMod(mclBnFp *x, const void *buf, mclSize bufSize);
 
 // return 1 if true and 0 otherwise
 MCLBN_DLL_API int mclBnFr_isValid(const mclBnFr *x);
diff --git a/include/mcl/fp.hpp b/include/mcl/fp.hpp
index 5de0dfb..96110a8 100644
--- a/include/mcl/fp.hpp
+++ b/include/mcl/fp.hpp
@@ -408,6 +408,31 @@ public:
 		}
 		return n;
 	}
+	/*
+		set (little endian % p)
+		error if bufSize > 64
+	*/
+	void setLittleEndianMod(bool *pb, const void *buf, size_t bufSize)
+	{
+		setArray(pb, (const char *)buf, bufSize, mcl::fp::Mod);
+	}
+	/*
+		set (big endian % p)
+		error if bufSize > 64
+	*/
+	void setBigEndianMod(bool *pb, const void *buf, size_t bufSize)
+	{
+		if (bufSize > 64) {
+			*pb = false;
+			return;
+		}
+		const uint8_t *p = (const uint8_t*)buf;
+		uint8_t swapBuf[64];
+		for (size_t i = 0; i < bufSize; i++) {
+			swapBuf[bufSize - 1 - i] = p[i];
+		}
+		setArray(pb, swapBuf, bufSize, mcl::fp::Mod);
+	}
 	void setByCSPRNG(bool *pb, fp::RandGen rg = fp::RandGen())
 	{
 		if (rg.isZero()) rg = fp::RandGen::get();
@@ -416,6 +441,18 @@ public:
 		setArrayMask(v_, op_.N);
 	}
 #ifndef CYBOZU_DONT_USE_EXCEPTION
+	void setLittleEndianMod(const void *buf, size_t bufSize)
+	{
+		bool b;
+		setLittleEndianMod(&b, buf, bufSize, mcl::fp::Mod);
+		if (!b) throw cybozu::Exception("setLittleEndianMod");
+	}
+	void setBigEndianMod(const void *buf, size_t bufSize)
+	{
+		bool b;
+		setBigEndianMod(&b, buf, bufSize, mcl::fp::Mod);
+		if (!b) throw cybozu::Exception("setBigEndianMod");
+	}
 	void setByCSPRNG(fp::RandGen rg = fp::RandGen())
 	{
 		bool b;
diff --git a/include/mcl/impl/bn_c_impl.hpp b/include/mcl/impl/bn_c_impl.hpp
index f31380b..d601861 100644
--- a/include/mcl/impl/bn_c_impl.hpp
+++ b/include/mcl/impl/bn_c_impl.hpp
@@ -748,7 +748,14 @@ int mclBnFp_setLittleEndian(mclBnFp *x, const void *buf, mclSize bufSize)
 int mclBnFp_setLittleEndianMod(mclBnFp *x, const void *buf, mclSize bufSize)
 {
 	bool b;
-	cast(x)->setArray(&b, (const char *)buf, bufSize, mcl::fp::Mod);
+	cast(x)->setLittleEndianMod(&b, buf, bufSize);
+	return b ? 0 : -1;
+}
+
+int mclBnFp_setBigEndianMod(mclBnFp *x, const void *buf, mclSize bufSize)
+{
+	bool b;
+	cast(x)->setBigEndianMod(&b, buf, bufSize);
 	return b ? 0 : -1;
 }
 
diff --git a/include/mcl/mapto_wb19.hpp b/include/mcl/mapto_wb19.hpp
index 45e31c8..6b353bc 100644
--- a/include/mcl/mapto_wb19.hpp
+++ b/include/mcl/mapto_wb19.hpp
@@ -30,9 +30,8 @@ inline void hashToFp2old(Fp2& out, const void *msg, size_t msgSize, uint8_t ctr,
 		info_pfx[4] = char(i + 1);
 		uint8_t t[64];
 		fp::hkdf_expand(t, msg_prime, info_pfx);
-		fp::local::byteSwap(t, 64);
 		bool b;
-		out.getFp0()[i].setArrayMod(&b, t, 64);
+		out.getFp0()[i].setBigEndianMod(&b, t, 64);
 		assert(b); (void)b;
 	}
 }
@@ -450,10 +449,8 @@ struct MapToG2_WB19 {
 		}
 		Fp *x = out[0].getFp0();
 		for (size_t i = 0; i < 4; i++) {
-			uint8_t *p = &md[64 * i];
-			fp::local::byteSwap(p, 64);
 			bool b;
-			x[i].setArrayMod(&b, p, 64);
+			x[i].setBigEndianMod(&b, &md[64 * i], 64);
 			assert(b); (void)b;
 		}
 	}