From e63dcc3a6752e7d406e7a650c2d6c2e95cd39aab Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Thu, 18 Jun 2020 16:31:08 -0700
Subject: [PATCH] Add MakeUCharSpan, to help constructing Span<[const] unsigned
 char>

Based on a suggestion by Russell Yanofsky.
---
 src/span.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/span.h b/src/span.h
index 79f13c9203..4afb383a59 100644
--- a/src/span.h
+++ b/src/span.h
@@ -207,4 +207,16 @@ T& SpanPopBack(Span<T>& span)
     return back;
 }
 
+// Helper functions to safely cast to unsigned char pointers.
+inline unsigned char* UCharCast(char* c) { return (unsigned char*)c; }
+inline unsigned char* UCharCast(unsigned char* c) { return c; }
+inline const unsigned char* UCharCast(const char* c) { return (unsigned char*)c; }
+inline const unsigned char* UCharCast(const unsigned char* c) { return c; }
+
+// Helper function to safely convert a Span to a Span<[const] unsigned char>.
+template <typename T> constexpr auto UCharSpanCast(Span<T> s) -> Span<typename std::remove_pointer<decltype(UCharCast(s.data()))>::type> { return {UCharCast(s.data()), s.size()}; }
+
+/** Like MakeSpan, but for (const) unsigned char member types only. Only works for (un)signed char containers. */
+template <typename V> constexpr auto MakeUCharSpan(V&& v) -> decltype(UCharSpanCast(MakeSpan(std::forward<V>(v)))) { return UCharSpanCast(MakeSpan(std::forward<V>(v))); }
+
 #endif