From b26721213d8e31fbef342ad7ad24b9972cb95bb8 Mon Sep 17 00:00:00 2001
From: Cheng <ChengSheng@fakemail.ch>
Date: Sat, 2 Apr 2022 13:38:06 +1100
Subject: [PATCH] still playing around with the mysterious, complicated, and
 unpredictable effects of std::enable_if_t

---
 introspection_of_standard_C_types.h |  7 ++++++-
 ristretto255.h                      | 11 ++++++-----
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/introspection_of_standard_C_types.h b/introspection_of_standard_C_types.h
index 6f82b9b..f00822d 100644
--- a/introspection_of_standard_C_types.h
+++ b/introspection_of_standard_C_types.h
@@ -25,7 +25,12 @@ namespace ro {
 
 	template <class T, class U = std::enable_if_t<is_standard_integer<T>,std::make_unsigned<std::remove_cvref_t<T>>::type>>
 	constexpr U iabs(T i) {
-		if constexpr (is_standard_signed_integer<T>)return U(abs(i));
+		if constexpr (is_standard_signed_integer<T>) {
+			U j;
+			if (i < 0)j = -i;
+			else j = i;
+			return j;
+			}
 		else return i;
 	}
 
diff --git a/ristretto255.h b/ristretto255.h
index 23bb41e..d0374ee 100644
--- a/ristretto255.h
+++ b/ristretto255.h
@@ -654,11 +654,12 @@ namespace ristretto255 {
 		explicit constexpr scalar(std::array<uint8_t, crypto_core_ristretto255_BYTES>&& in) : blob{ in } {};
 		explicit constexpr scalar(std::array<uint8_t, crypto_core_ristretto255_BYTES>* in) :blob(*in) {};
 		explicit constexpr scalar(uintmax_t k){ for (auto& j : blob) { j = k; k = k >> 8; } }
-		template <class T, class U = std::enable_if_t<ro::is_standard_integer<T>, uintmax_t>>
-		explicit constexpr scalar(T i) :scalar(U(ro::iabs<T>(i))) {
-			if constexpr (ro::is_standard_signed_integer<T>) {
-				if (i < 0) crypto_core_ristretto255_scalar_negate(&blob[0], &blob[0]);
-			}
+		template <class T>
+		explicit constexpr scalar(std::enable_if_t < ro::is_standard_unsigned_integer<T>, T> i) :scalar(uintmax_t(i)) {}
+		template <class T, class U = std::enable_if_t<ro::is_standard_signed_integer<T>, uintmax_t>>
+		explicit constexpr scalar(T i) : scalar(U(ro::iabs<T>(i))) {
+			static_assert (ro::is_standard_signed_integer<T>);
+			if (i < 0) crypto_core_ristretto255_scalar_negate(&blob[0], &blob[0]);
 		}
 		scalar(scalar&&) = default;	// Move constructor
 		scalar(const scalar&) = default;	// Copy constructor